On Fri, Jul 24, 2026 at 9:19 AM Konstantinos Eleftheriou
<[email protected]> wrote:
>
> Hi Andrew,
>
> On Fri, Jul 24, 2026 at 3:53 AM Andrea Pinski
> <[email protected]> wrote:
>>
>> On Tue, Jul 14, 2026 at 9:05 AM Konstantinos Eleftheriou
>> <[email protected]> wrote:
>> >
>> > Recognize the longhand wide-multiplication carry idiom and fold it to a
>> > widening multiply followed by a right shift for the high part, and a
>> > plain MULT_EXPR for the low part.
>> >
>> > The carry idiom is the schoolbook expansion of a 2N-bit unsigned
>> > multiply written as a top-level + chain of four NxN partial products
>> > plus one overflow-compare carry:
>> >
>> > xh*yh + (cross_sum >> N) + (low_accum >> N) + ((hilo > cross_sum) << N)
>> > cross_sum = xh*yl + xl*yh
>> > low_accum = (xl*yl >> N) + (cross_sum & mask)
>> >
>> > For example, this AArch64 sequence from SPEC2026's 750.sealcrypto_r:
>> >
>> > lsr x4, x0, 32
>> > lsr x6, x1, 32
>> > umull x3, w0, w1
>> > umull x1, w1, w4
>> > and x5, x3, 4294967295
>> > umaddl x0, w0, w6, x1
>> > cmp x1, x0
>> > and x1, x0, 4294967295
>> > lsr x0, x0, 32
>> > add x3, x1, x3, lsr 32
>> > cset x1, hi
>> > orr x5, x5, x3, lsl 32
>> > umaddl x4, w4, w6, x0
>> > extr x0, x1, x3, 32
>> > add x0, x0, x4
>> > stp x5, x0, [x2]
>> >
>> > can be transformed to:
>> >
>> > umulh x3, x1, x0
>> > mul x0, x0, x1
>> > stp x0, x3, [x2]
>> >
>> > Atom-level pattern recognition is implemented via match patterns in
>> > match.pd (mul_hi, mul_lo, mul_hilo, mul_lolo, mul_hihi, mul_cross_sum,
>> > mul_low_accum, mul_carry_cross_sum). The composite recognition that
>> > ties atoms into a long-multiplication chain is performed in forwprop
>> > by match_long_mul: it linearizes the outer add/ior chain into a
>> > multiset of summands, classifies each summand via the match.pd atoms,
>> > and looks the multiset up in long_mul_table to identify the variant.
>> > On a hit, three cross-summand consistency checks (one operand pair,
>> > half-width shifts, hilo cross-half products) gate the rewrite.
>> >
>> > The HIGH_PART row emits the canonical widening shape
>> >
>> > (N)(((2N) op1 * (2N) op2) >> N)
>> >
>> > which pass_optimize_widening_mul later lowers to a single
>> > WIDEN_MULT_EXPR or MULT_HIGHPART_EXPR on targets that support it.
>> > The LOW_PART row emits a plain MULT_EXPR. HIGH_PART is emitted only
>> > when the 2N mode is present in the mode table.
>> >
>> > Bootstrapped/regtested on AArch64, x86-64 and PowerPC.
>> >
>> > PR tree-optimization/107090
>> >
>> > gcc/ChangeLog:
>> >
>> > * match.pd: Add atom match recognizers for long-multiply
>> > (mul_hi, mul_lo, mul_hilo, mul_lolo, mul_hihi, mul_cross_sum,
>> > mul_low_accum, mul_carry_cross_sum).
>> > * tree-ssa-forwprop.cc (gimple_mul_hi): Declare.
>> > (gimple_mul_lo): Likewise.
>> > (gimple_mul_hilo): Likewise.
>> > (gimple_mul_lolo): Likewise.
>> > (gimple_mul_hihi): Likewise.
>> > (gimple_mul_cross_sum): Likewise.
>> > (gimple_mul_low_accum): Likewise.
>> > (gimple_mul_carry_cross_sum): Likewise.
>> > (create_mul_high_seq): New, emits (N)(((2N) op1 * (2N) op2) >> N).
>> > (create_mul_low_seq): New, emits MULT_EXPR.
>> > (enum long_mul_kind): New.
>> > (enum long_mul_extract): New.
>> > (struct long_mul_summand): New.
>> > (long_mul_linearize_chain): New, walks the outer add/ior chain
>> > into a multiset of leaves.
>> > (long_mul_is_lshift_def): New.
>> > (long_mul_set_summand): New.
>> > (long_mul_classify_carry): New.
>> > (long_mul_classify_plus_kinds): New.
>> > (long_mul_classify_hi_extract): New.
>> > (long_mul_classify_lo_extract): New.
>> > (long_mul_classify_shl_extract): New.
>> > (long_mul_classify_bare): New.
>> > (long_mul_classify_summand): New, classify each summand via the
>> > match.pd atoms.
>> > (long_mul_summand_compare): New.
>> > (struct long_mul_row): New.
>> > (long_mul_same_ops): New.
>> > (long_mul_is_cross_half): New.
>> > (long_mul_hilo_orientation): New, orientation of a mul_hilo
>> > capture relative to (op0, op1).
>> > (long_mul_canonical_ops): New.
>> > (long_mul_check_consistency): New, cross-summand consistency
>> > check (operand pairing, half-width shifts, hilo cross-half).
>> > (long_mul_signature_matches): New.
>> > (long_mul_hint_shared_intermediate): New, dump-file hint
>> > pointing at a shared inner addition.
>> > (match_long_mul): New, top-level entry: linearizes the outer
>> > add/ior chain, classifies summands, looks the multiset up in
>> > long_mul_table, runs cross-summand consistency checks, and
>> > dispatches to create_mul_high_seq / create_mul_low_seq.
>> > (pass_forwprop::execute): Call match_long_mul on PLUS_EXPR and
>> > BIT_IOR_EXPR statements.
>> >
>> > gcc/testsuite/ChangeLog:
>> >
>> > * gcc.dg/tree-ssa/long-mul-carry.c: New test.
>> > * gcc.target/aarch64/long_mul.c: New test.
>> > * gcc.target/i386/long_mul.c: New test.
>> >
>> > Co-authored-by: Philipp Tomsich <[email protected]>
>> > Signed-off-by: Konstantinos Eleftheriou <[email protected]>
>> > ---
>> >
>> > (no changes since v1)
>> >
>> > gcc/match.pd | 73 ++
>> > .../gcc.dg/tree-ssa/long-mul-carry.c | 181 +++++
>> > gcc/testsuite/gcc.target/aarch64/long_mul.c | 58 ++
>> > gcc/testsuite/gcc.target/i386/long_mul.c | 58 ++
>> > gcc/tree-ssa-forwprop.cc | 701 +++++++++++++++++-
>> > 5 files changed, 1066 insertions(+), 5 deletions(-)
>> > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/long-mul-carry.c
>> > create mode 100644 gcc/testsuite/gcc.target/aarch64/long_mul.c
>> > create mode 100644 gcc/testsuite/gcc.target/i386/long_mul.c
>> >
>> > diff --git a/gcc/match.pd b/gcc/match.pd
>> > index 9d4ab622fe57..5a4b1923b589 100644
>> > --- a/gcc/match.pd
>> > +++ b/gcc/match.pd
>> > @@ -12160,6 +12160,79 @@ and,
>> > INTEGER_CST@2) INTEGER_CST@3)
>> > (if (compare_tree_int (@sub1, 1) == 0)))
>> >
>> > +#if GIMPLE
>> > +/* Match low and high parts of longhand multiplication.
>> > + Given a 2N-bit unsigned type, x = xh*2^N + xl and y = yh*2^N + yl,
>> > + where xh, xl, yh, yl are N-bit halves extracted via shifts and masks.
>> > */
>> > +
>> > +/* High half: op >> N. */
>> > +(match (mul_hi @op @0)
>> > + (rshift @op INTEGER_CST@0)
>> > + (with {
>> > + tree op_type = TREE_TYPE (@op); }
>> > + (if (INTEGRAL_TYPE_P (op_type)
>> > + && TYPE_UNSIGNED (op_type)
>> > + && TYPE_PRECISION (op_type) % 2 == 0
>> > + && tree_fits_uhwi_p (@0)
>> > + && tree_to_uhwi (@0) == TYPE_PRECISION (op_type) / 2))))
>> > +/* Low half: op & mask. */
>> > +(match (mul_lo @op @0)
>> > + (bit_and @op INTEGER_CST@0)
>> > + (with {
>> > + tree op_type = TREE_TYPE (@op); }
>> > + (if (INTEGRAL_TYPE_P (op_type)
>> > + && TYPE_UNSIGNED (op_type)
>> > + && TYPE_PRECISION (op_type) % 2 == 0
>> > + && tree_fits_uhwi_p (@0)
>> > + && tree_to_uhwi (@0) == wi::mask (
>> > + TYPE_PRECISION (op_type) / 2,
>> > + false,
>> > + TYPE_PRECISION (op_type))))))
>> > +/* Cross product: high(op0) * low(op1). */
>> > +(match (mul_hilo @op0 @op1 @0 @1)
>> > + (mult:c
>> > + (mul_hi @op0 INTEGER_CST@0)
>> > + (mul_lo @op1 INTEGER_CST@1)))
>> > +/* Low-low product: low(op0) * low(op1). */
>> > +(match (mul_lolo @op0 @op1 @0)
>> > + (mult:c
>> > + (mul_lo @op0 INTEGER_CST@0)
>> > + (mul_lo @op1 INTEGER_CST@0)))
>> > +/* High-high product: high(op0) * high(op1). */
>> > +(match (mul_hihi @op0 @op1 @0)
>> > + (mult:c
>> > + (mul_hi @op0 INTEGER_CST@0)
>> > + (mul_hi @op1 INTEGER_CST@0)))
>> > +/* Cross sum: xh*yl + xl*yh.
>> > + Note: matches any PLUS; operands are validated as actual cross
>> > + products by the forwprop consumer (long_mul_check_consistency). */
>> > +(match (mul_cross_sum @mul_hilo0 @mul_hilo1)
>> > + (plus:c @mul_hilo0 @mul_hilo1))
>> > +/* Carry from cross-sum overflow: (cast?) (hilo > cross_sum) << N.
>> > + Explicit guard required because mul_cross_sum is just (plus:c @0 @1)
>> > + with no inherent type or halfwidth constraint. */
>> > +(match (mul_carry_cross_sum @mul_hilo0 @mul_hilo1 @mul_hilo2 @0)
>> > + (lshift
>> > + (convert? (gt
>> > + @mul_hilo0
>> > + (mul_cross_sum @mul_hilo1 @mul_hilo2)))
>> > + INTEGER_CST@0)
>> > + (with {
>> > + tree op_type = TREE_TYPE (@mul_hilo0); }
>> > + (if (INTEGRAL_TYPE_P (op_type)
>> > + && TYPE_UNSIGNED (op_type)
>> > + && TYPE_PRECISION (op_type) % 2 == 0
>> > + && tree_fits_uhwi_p (@0)
>> > + && tree_to_uhwi (@0) == TYPE_PRECISION (op_type) / 2))))
>> > +/* Low accumulate: (xl*yl >> N) + (cross_sum & mask). */
>> > +(match (mul_low_accum @op0 @op1 @mul_hilo0 @mul_hilo1 @0 @1)
>> > + (plus:c
>> > + (mul_hi
>> > + (mul_lolo @op0 @op1 INTEGER_CST@0)
>> > + INTEGER_CST@1)
>> > + (mul_lo (mul_cross_sum @mul_hilo0 @mul_hilo1) INTEGER_CST@0)))
>> > +#endif
>> > +
>> > /* Floatint point/integer comparison and integer->integer
>> > or floating point -> float point conversion. */
>> > (match (cond_expr_convert_p @0 @2 @3 @6)
>> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/long-mul-carry.c
>> > b/gcc/testsuite/gcc.dg/tree-ssa/long-mul-carry.c
>> > new file mode 100644
>> > index 000000000000..bbdbc63ac0bb
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/long-mul-carry.c
>> > @@ -0,0 +1,181 @@
>> > +/* { dg-do compile } */
>> > +/* { dg-options "-O3 -fdump-tree-forwprop-details" } */
>> > +
>> > +typedef __UINT32_TYPE__ uint32_t;
>> > +typedef __UINT64_TYPE__ uint64_t;
>> > +typedef struct { uint32_t v[2]; } v2i32;
>> > +
>> > +/* High part follows the long form
>> > + xh*yh + carry + (cross_sum >> N) + (low_accum >> N). */
>> > +
>> > +uint64_t mulh_carry (uint64_t x, uint64_t y)
>> > +{
>> > + uint64_t x_lo = x & 0xFFFFFFFF;
>> > + uint64_t x_hi = x >> 32;
>> > + uint64_t y_lo = y & 0xFFFFFFFF;
>> > + uint64_t y_hi = y >> 32;
>> > + uint64_t y_lo_x_hi = y_lo * x_hi;
>> > + uint64_t y_hi_x_hi = y_hi * x_hi;
>> > + uint64_t y_hi_x_lo = y_hi * x_lo;
>> > + uint64_t y_lo_x_lo = y_lo * x_lo;
>> > + uint64_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = cross_sum < y_lo_x_hi;
>> > + uint64_t carry = (uint64_t) carry_out << 32;
>> > + uint64_t y_lo_x_lo_hi = y_lo_x_lo >> 32;
>> > + uint64_t cross_sum_lo = cross_sum & 0xFFFFFFFF;
>> > + uint64_t cross_sum_hi = cross_sum >> 32;
>> > + uint64_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + uint64_t interm = cross_sum_hi + y_hi_x_hi;
>> > + uint64_t low_accum_hi = low_accum >> 32;
>> > + uint64_t interm_plus_carry = interm + carry;
>> > + uint64_t hw64 = interm_plus_carry + low_accum_hi;
>> > +
>> > + return hw64;
>> > +}
>> > +
>> > +uint64_t mulh_carry_comm (uint64_t x, uint64_t y)
>> > +{
>> > + uint64_t x_lo = x & 0xFFFFFFFF;
>> > + uint64_t y_lo = y & 0xFFFFFFFF;
>> > + uint64_t x_hi = x >> 32;
>> > + uint64_t y_hi = y >> 32;
>> > + uint64_t y_lo_x_hi = x_hi * y_lo;
>> > + uint64_t y_hi_x_hi = y_hi * x_hi;
>> > + uint64_t y_hi_x_lo = x_lo * y_hi;
>> > + uint64_t y_lo_x_lo = x_lo * y_lo;
>> > + uint64_t cross_sum = y_lo_x_hi + y_hi_x_lo;
>> > + int carry_out = (cross_sum < y_lo_x_hi);
>> > + uint64_t carry = (uint64_t) carry_out << 32;
>> > + uint64_t y_lo_x_lo_hi = y_lo_x_lo >> 32;
>> > + uint64_t cross_sum_lo = cross_sum & 0xFFFFFFFF;
>> > + uint64_t cross_sum_hi = cross_sum >> 32;
>> > + uint64_t low_accum = y_lo_x_lo_hi + cross_sum_lo;
>> > + uint64_t inter = y_hi_x_hi + cross_sum_hi;
>> > + uint64_t low_accum_hi = low_accum >> 32;
>> > + uint64_t interm_plus_carry = carry + inter;
>> > + uint64_t hw64 = low_accum_hi + interm_plus_carry;
>> > +
>> > + return hw64;
>> > +}
>> > +
>> > +uint32_t mulh_carry_32 (uint32_t x, uint32_t y)
>> > +{
>> > + uint32_t x_lo = x & 0xFFFF;
>> > + uint32_t x_hi = x >> 16;
>> > + uint32_t y_lo = y & 0xFFFF;
>> > + uint32_t y_hi = y >> 16;
>> > + uint32_t y_lo_x_hi = y_lo * x_hi;
>> > + uint32_t y_hi_x_hi = y_hi * x_hi;
>> > + uint32_t y_hi_x_lo = y_hi * x_lo;
>> > + uint32_t y_lo_x_lo = y_lo * x_lo;
>> > + uint32_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = (cross_sum < y_lo_x_hi);
>> > + uint32_t carry = (uint32_t) carry_out << 16;
>> > + uint32_t y_lo_x_lo_hi = y_lo_x_lo >> 16;
>> > + uint32_t cross_sum_lo = cross_sum & 0xFFFF;
>> > + uint32_t cross_sum_hi = cross_sum >> 16;
>> > + uint32_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + uint32_t interm = cross_sum_hi + y_hi_x_hi;
>> > + uint32_t low_accum_hi = low_accum >> 16;
>> > + uint32_t interm_plus_carry = interm + carry;
>> > + uint32_t hw64 = interm_plus_carry + low_accum_hi;
>> > +
>> > + return hw64;
>> > +}
>> > +
>> > +/* The 128-bit variant lowers to longhand in pass_optimize_widening_mul;
>> > + no target provides a 256-bit multiply. */
>> > +#ifdef __SIZEOF_INT128__
>> > +__uint128_t mulh_carry_128 (__uint128_t x, __uint128_t y)
>> > +{
>> > + __uint128_t x_lo = x & (__uint128_t)0xFFFFFFFFFFFFFFFF;
>> > + __uint128_t x_hi = x >> 64;
>> > + __uint128_t y_lo = y & (__uint128_t)0xFFFFFFFFFFFFFFFF;
>> > + __uint128_t y_hi = y >> 64;
>> > + __uint128_t y_lo_x_hi = y_lo * x_hi;
>> > + __uint128_t y_hi_x_hi = y_hi * x_hi;
>> > + __uint128_t y_hi_x_lo = y_hi * x_lo;
>> > + __uint128_t y_lo_x_lo = y_lo * x_lo;
>> > + __uint128_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = cross_sum < y_lo_x_hi;
>> > + __uint128_t carry = (__uint128_t) carry_out << 64;
>> > + __uint128_t y_lo_x_lo_hi = y_lo_x_lo >> 64;
>> > + __uint128_t cross_sum_lo = cross_sum & (__uint128_t)0xFFFFFFFFFFFFFFFF;
>> > + __uint128_t cross_sum_hi = cross_sum >> 64;
>> > + __uint128_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + __uint128_t interm = cross_sum_hi + y_hi_x_hi;
>> > + __uint128_t low_accum_hi = low_accum >> 64;
>> > + __uint128_t interm_plus_carry = interm + carry;
>> > + __uint128_t hw64 = interm_plus_carry + low_accum_hi;
>> > +
>> > + return hw64;
>> > +}
>> > +#endif
>> > +
>> > +void full_mul_carry (uint64_t x, uint64_t y, uint64_t* p) {
>> > + uint64_t x_lo = x & 0xFFFFFFFF;
>> > + uint64_t y_lo = y & 0xFFFFFFFF;
>> > + uint64_t x_hi = x >> 32;
>> > + uint64_t y_hi = y >> 32;
>> > + uint64_t y_lo_x_hi = y_lo * x_hi;
>> > + uint64_t y_hi_x_hi = y_hi * x_hi;
>> > + uint64_t y_hi_x_lo = y_hi * x_lo;
>> > + uint64_t y_lo_x_lo = y_lo * x_lo;
>> > + uint64_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = (cross_sum < y_lo_x_hi);
>> > + uint64_t carry = (uint64_t) carry_out << 32;
>> > + uint64_t y_lo_x_lo_hi = y_lo_x_lo >> 32;
>> > + uint64_t cross_sum_lo = cross_sum & 0xFFFFFFFF;
>> > + uint64_t cross_sum_hi = cross_sum >> 32;
>> > + uint64_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + uint64_t upper_mid = y_hi_x_hi + carry;
>> > + uint64_t low_accum_hi = low_accum >> 32;
>> > + uint64_t upper_mid_with_cross = upper_mid + cross_sum_hi;
>> > + uint64_t hw64 = upper_mid_with_cross + low_accum_hi;
>> > + p[1] = hw64;
>> > + uint64_t low_accum_shifted = low_accum << 32;
>> > + uint64_t y_lo_x_lo_lo = y_lo_x_lo & 0xFFFFFFFF;
>> > + uint64_t lw64 = low_accum_shifted | y_lo_x_lo_lo;
>> > + p[0] = lw64;
>> > +}
>> > +
>> > +/* This will be optimized during the second forwprop run.
>> > + Disable SLP so the expected fold count is target-independent. */
>> > +__attribute__((optimize("no-tree-slp-vectorize")))
>> > +v2i32 mulh_carry_v2i32 (v2i32 x, v2i32 y)
>> > +{
>> > + v2i32 result;
>> > + for (int i = 0; i < 2; i++)
>> > + {
>> > + uint32_t x_lo = x.v[i] & 0xFFFF;
>> > + uint32_t y_lo = y.v[i] & 0xFFFF;
>> > + uint32_t x_hi = x.v[i] >> 16;
>> > + uint32_t y_hi = y.v[i] >> 16;
>> > +
>> > + uint32_t y_lo_x_hi = y_lo * x_hi;
>> > + uint32_t y_hi_x_hi = y_hi * x_hi;
>> > + uint32_t y_hi_x_lo = y_hi * x_lo;
>> > + uint32_t y_lo_x_lo = y_lo * x_lo;
>> > +
>> > + uint32_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = cross_sum < y_lo_x_hi;
>> > + uint32_t carry = (uint32_t) carry_out << 16;
>> > +
>> > + uint32_t y_lo_x_lo_hi = y_lo_x_lo >> 16;
>> > + uint32_t cross_sum_lo = cross_sum & 0xFFFF;
>> > + uint32_t cross_sum_hi = cross_sum >> 16;
>> > +
>> > + uint32_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + uint32_t interm = cross_sum_hi + y_hi_x_hi;
>> > + uint32_t low_accum_hi = low_accum >> 16;
>> > + uint32_t interm_plus_carry = interm + carry;
>> > +
>> > + result.v[i] = interm_plus_carry + low_accum_hi;
>> > + }
>> > +
>> > + return result;
>> > +}
>> > +
>> > +/* { dg-final { scan-tree-dump-times "Long multiplication high part
>> > folded." 4 "forwprop1" } } */
>> > +/* { dg-final { scan-tree-dump-times "Long multiplication high part
>> > folded." 1 "forwprop2" } } */
>> > +/* { dg-final { scan-tree-dump-times "Long multiplication low part
>> > folded." 1 "forwprop1" } } */
>> > diff --git a/gcc/testsuite/gcc.target/aarch64/long_mul.c
>> > b/gcc/testsuite/gcc.target/aarch64/long_mul.c
>> > new file mode 100644
>> > index 000000000000..2a4709ecbfd0
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.target/aarch64/long_mul.c
>> > @@ -0,0 +1,58 @@
>> > +/* { dg-do compile } */
>> > +/* { dg-options "-O3" } */
>> > +
>> > +typedef __UINT32_TYPE__ uint32_t;
>> > +typedef __UINT64_TYPE__ uint64_t;
>> > +
>> > +/* 64-bit carry pattern for high part. */
>> > +uint64_t mulh_carry (uint64_t x, uint64_t y)
>> > +{
>> > + uint64_t x_lo = x & 0xFFFFFFFF;
>> > + uint64_t x_hi = x >> 32;
>> > + uint64_t y_lo = y & 0xFFFFFFFF;
>> > + uint64_t y_hi = y >> 32;
>> > + uint64_t y_lo_x_hi = y_lo * x_hi;
>> > + uint64_t y_hi_x_hi = y_hi * x_hi;
>> > + uint64_t y_hi_x_lo = y_hi * x_lo;
>> > + uint64_t y_lo_x_lo = y_lo * x_lo;
>> > + uint64_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = cross_sum < y_lo_x_hi;
>> > + uint64_t carry = (uint64_t) carry_out << 32;
>> > + uint64_t y_lo_x_lo_hi = y_lo_x_lo >> 32;
>> > + uint64_t cross_sum_lo = cross_sum & 0xFFFFFFFF;
>> > + uint64_t cross_sum_hi = cross_sum >> 32;
>> > + uint64_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + uint64_t interm = cross_sum_hi + y_hi_x_hi;
>> > + uint64_t low_accum_hi = low_accum >> 32;
>> > + uint64_t interm_plus_carry = interm + carry;
>> > + return interm_plus_carry + low_accum_hi;
>> > +}
>> > +
>> > +/* 32-bit carry pattern for high part. */
>> > +uint32_t mulh_carry_32 (uint32_t x, uint32_t y)
>> > +{
>> > + uint32_t x_lo = x & 0xFFFF;
>> > + uint32_t x_hi = x >> 16;
>> > + uint32_t y_lo = y & 0xFFFF;
>> > + uint32_t y_hi = y >> 16;
>> > + uint32_t y_lo_x_hi = y_lo * x_hi;
>> > + uint32_t y_hi_x_hi = y_hi * x_hi;
>> > + uint32_t y_hi_x_lo = y_hi * x_lo;
>> > + uint32_t y_lo_x_lo = y_lo * x_lo;
>> > + uint32_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = (cross_sum < y_lo_x_hi);
>> > + uint32_t carry = (uint32_t) carry_out << 16;
>> > + uint32_t y_lo_x_lo_hi = y_lo_x_lo >> 16;
>> > + uint32_t cross_sum_lo = cross_sum & 0xFFFF;
>> > + uint32_t cross_sum_hi = cross_sum >> 16;
>> > + uint32_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + uint32_t interm = cross_sum_hi + y_hi_x_hi;
>> > + uint32_t low_accum_hi = low_accum >> 16;
>> > + uint32_t interm_plus_carry = interm + carry;
>> > + return interm_plus_carry + low_accum_hi;
>> > +}
>> > +
>> > +/* 64-bit pattern should emit umulh. */
>> > +/* { dg-final { scan-assembler-times "umulh\t" 1 } } */
>> > +/* 32-bit pattern should emit umull (32x32->64 widening multiply). */
>> > +/* { dg-final { scan-assembler-times "umull\t" 1 } } */
>> > diff --git a/gcc/testsuite/gcc.target/i386/long_mul.c
>> > b/gcc/testsuite/gcc.target/i386/long_mul.c
>> > new file mode 100644
>> > index 000000000000..6ec87eb8dd21
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.target/i386/long_mul.c
>> > @@ -0,0 +1,58 @@
>> > +/* { dg-do compile { target { ! ia32 } } } */
>> > +/* { dg-options "-O3" } */
>> > +
>> > +typedef __UINT32_TYPE__ uint32_t;
>> > +typedef __UINT64_TYPE__ uint64_t;
>> > +
>> > +/* 64-bit carry pattern for high part. */
>> > +uint64_t mulh_carry (uint64_t x, uint64_t y)
>> > +{
>> > + uint64_t x_lo = x & 0xFFFFFFFF;
>> > + uint64_t x_hi = x >> 32;
>> > + uint64_t y_lo = y & 0xFFFFFFFF;
>> > + uint64_t y_hi = y >> 32;
>> > + uint64_t y_lo_x_hi = y_lo * x_hi;
>> > + uint64_t y_hi_x_hi = y_hi * x_hi;
>> > + uint64_t y_hi_x_lo = y_hi * x_lo;
>> > + uint64_t y_lo_x_lo = y_lo * x_lo;
>> > + uint64_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = cross_sum < y_lo_x_hi;
>> > + uint64_t carry = (uint64_t) carry_out << 32;
>> > + uint64_t y_lo_x_lo_hi = y_lo_x_lo >> 32;
>> > + uint64_t cross_sum_lo = cross_sum & 0xFFFFFFFF;
>> > + uint64_t cross_sum_hi = cross_sum >> 32;
>> > + uint64_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + uint64_t interm = cross_sum_hi + y_hi_x_hi;
>> > + uint64_t low_accum_hi = low_accum >> 32;
>> > + uint64_t interm_plus_carry = interm + carry;
>> > + return interm_plus_carry + low_accum_hi;
>> > +}
>> > +
>> > +/* 32-bit carry pattern for high part. */
>> > +uint32_t mulh_carry_32 (uint32_t x, uint32_t y)
>> > +{
>> > + uint32_t x_lo = x & 0xFFFF;
>> > + uint32_t x_hi = x >> 16;
>> > + uint32_t y_lo = y & 0xFFFF;
>> > + uint32_t y_hi = y >> 16;
>> > + uint32_t y_lo_x_hi = y_lo * x_hi;
>> > + uint32_t y_hi_x_hi = y_hi * x_hi;
>> > + uint32_t y_hi_x_lo = y_hi * x_lo;
>> > + uint32_t y_lo_x_lo = y_lo * x_lo;
>> > + uint32_t cross_sum = y_hi_x_lo + y_lo_x_hi;
>> > + int carry_out = (cross_sum < y_lo_x_hi);
>> > + uint32_t carry = (uint32_t) carry_out << 16;
>> > + uint32_t y_lo_x_lo_hi = y_lo_x_lo >> 16;
>> > + uint32_t cross_sum_lo = cross_sum & 0xFFFF;
>> > + uint32_t cross_sum_hi = cross_sum >> 16;
>> > + uint32_t low_accum = cross_sum_lo + y_lo_x_lo_hi;
>> > + uint32_t interm = cross_sum_hi + y_hi_x_hi;
>> > + uint32_t low_accum_hi = low_accum >> 16;
>> > + uint32_t interm_plus_carry = interm + carry;
>> > + return interm_plus_carry + low_accum_hi;
>> > +}
>> > +
>> > +/* 64-bit pattern should emit mulq (unsigned 64x64->128 multiply). */
>> > +/* { dg-final { scan-assembler-times "\tmulq" 1 } } */
>> > +/* 32-bit pattern should emit imulq (64-bit multiply of zero-extended
>> > operands). */
>> > +/* { dg-final { scan-assembler-times "\timulq" 1 } } */
>> > diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
>> > index 12c07c99c9bd..3870bf17c0e0 100644
>> > --- a/gcc/tree-ssa-forwprop.cc
>> > +++ b/gcc/tree-ssa-forwprop.cc
>> > @@ -3592,6 +3592,693 @@ simplify_count_zeroes (gimple_stmt_iterator *gsi)
>> > return true;
>> > }
>> >
>> > +/* Match.pd functions to match long multiplication. */
>> > +
>> > +extern bool gimple_mul_hi (tree, tree *, tree (*)(tree));
>> > +extern bool gimple_mul_lo (tree, tree *, tree (*)(tree));
>> > +extern bool gimple_mul_hilo (tree, tree *, tree (*)(tree));
>> > +extern bool gimple_mul_lolo (tree, tree *, tree (*)(tree));
>> > +extern bool gimple_mul_hihi (tree, tree *, tree (*)(tree));
>> > +extern bool gimple_mul_cross_sum (tree, tree *, tree (*)(tree));
>> > +extern bool gimple_mul_low_accum (tree, tree *, tree (*)(tree));
>> > +extern bool gimple_mul_carry_cross_sum (tree, tree *, tree (*)(tree));
>> > +
>> > +/* Replace STMT with a high-part multiply of OP1 and OP2, emitted as
>> > + (N)(((2N) op1 * (2N) op2) >> N).
>> > + pass_optimize_widening_mul's convert_mult_to_widen and
>> > + convert_mult_to_highpart later rewrite this to a single
>> > + WIDEN_MULT_EXPR or MULT_HIGHPART_EXPR when the target supports it,
>> > + otherwise the 2N multiply expands directly. Emitting the canonical
>> > + widening shape keeps target-capability decisions in the layer that
>> > + already owns them. */
>> > +
>> > +static void
>> > +create_mul_high_seq (tree op1, tree op2, gimple *stmt)
>> > +{
>> > + tree op_type = TREE_TYPE (op1);
>> > + unsigned int width = TYPE_PRECISION (op_type);
>> > + tree wide_type = build_nonstandard_integer_type (width * 2, 1);
>> > +
>> > + location_t loc = gimple_location (stmt);
>> > + gimple_seq seq = NULL;
>> > +
>> > + tree wide_a = gimple_convert (&seq, loc, wide_type, op1);
>> > + tree wide_b = gimple_convert (&seq, loc, wide_type, op2);
>> > + tree wide_prod = gimple_build (&seq, loc, MULT_EXPR, wide_type,
>> > + wide_a, wide_b);
>> > + tree hi = gimple_build (&seq, loc, RSHIFT_EXPR, wide_type, wide_prod,
>> > + build_int_cst (integer_type_node, width));
>> > +
>> > + gimple *prod = gimple_build_assign (gimple_get_lhs (stmt), NOP_EXPR,
>> > hi);
>> > + gimple_set_location (prod, loc);
>> > + gimple_seq_add_stmt (&seq, prod);
>> > +
>> > + gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
>> > + gsi_replace_with_seq (&gsi, seq, true);
>> > +}
>> > +
>> > +/* Replace STMT with a low-part multiply of OP1 and OP2. */
>> > +
>> > +static void
>> > +create_mul_low_seq (tree op1, tree op2, gimple *stmt)
>> > +{
>> > + gimple *prod = gimple_build_assign (gimple_get_lhs (stmt),
>> > + MULT_EXPR, op1, op2);
>> > + gimple_set_location (prod, gimple_location (stmt));
>> > + gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
>> > + gsi_replace (&gsi, prod, true);
>> > +}
>> > +
>> > +/* Long-multiply fold framework.
>> > +
>> > + Walks the outer addition or bit_ior chain on a candidate statement,
>> > + classifies each summand against the atom match patterns from
>> > + match.pd, and looks the resulting multiset of (kind, extract) tuples
>> > + up in a table. On a hit, three cross-summand consistency checks
>> > + decide whether the wide multiply is emitted. */
>> > +
>> > +/* Widest match.pd atom (mul_low_accum) takes 6 captures; round up
>> > + to 8 for the scratch buffers below. */
>> > +static constexpr unsigned LONG_MUL_MAX_CAPTURES = 8;
>> > +
>> > +/* Longest variant in long_mul_table has 4 summands. */
>> > +static constexpr unsigned LONG_MUL_MAX_SUMMANDS = 4;
>> > +
>> > +enum long_mul_kind {
>> > + LMK_MUL_HIHI,
>> > + LMK_MUL_LOLO,
>> > + LMK_MUL_HILO,
>> > + LMK_CROSS_SUM,
>> > + LMK_LOW_ACCUM,
>> > + LMK_CARRY_CROSS_SUM,
>> > +};
>> > +
>> > +/* How the leaf wraps its inner kind. Carry kinds use LMX_NONE: their
>> > + match.pd pattern bakes the lshift in, so the leaf is already the
>> > + complete carry expression. */
>> > +
>> > +enum long_mul_extract {
>> > + LMX_NONE,
>> > + LMX_HI,
>> > + LMX_LO,
>> > + LMX_SHL_N,
>> > +};
>> > +
>> > +struct long_mul_summand {
>> > + long_mul_kind kind;
>> > + long_mul_extract extract;
>> > + tree op0, op1;
>> > + tree hilo0, hilo1, hilo2;
>> > + unsigned HOST_WIDE_INT shift;
>> > + unsigned HOST_WIDE_INT mask;
>> > +};
>> > +
>> > +/* Walk the OUTER addition or BIT_IOR chain rooted at STMT and collect
>> > + the leaf operands into LEAVES. Descends through single-use
>> > + intermediate stmts of the same code. Returns false once the leaf
>> > + count exceeds LONG_MUL_MAX_SUMMANDS, so an overlong chain bails
>> > + mid-walk instead of after a full traversal.
>> > +
>> > + If SHARED_DEF_OUT is non-NULL, record there the first inner stmt that
>> > + shares the outer code but has more than one use -- descending into it
>> > + would change semantics, so it stays as a leaf. Such a leaf often
>> > + classifies as something no row matches, silently disabling the fold;
>> > + the caller surfaces this as a dump-file hint. */
>> > +
>> > +static bool
>> > +long_mul_linearize_chain (gimple *stmt, tree_code outer, vec<tree>
>> > &leaves,
>> > + gimple **shared_def_out = NULL)
>> > +{
>> > + auto_vec<tree, 8> stack;
>> > + stack.safe_push (gimple_assign_rhs2 (stmt));
>> > + stack.safe_push (gimple_assign_rhs1 (stmt));
>> > +
>> > + while (!stack.is_empty ())
>> > + {
>>
>> The biggest problem I have with this patch is why do you need a worklist
>> here?
>
> That's not a worklist. It's a one-shot linearization of a single associative
> PLUS/OR
> into its summands. It runs once per root, holds at most 4 entries, and
> doesn't revisit statements.
>>
>> Since you are looking backwards and forwprop will retry the statement
>> if returns changed.
>
> There are no intermediate changes. We're not folding anything until the whole
> pattern
> matches.
>>
>> Do we need a worklist at all?
>
> We need the linearization. Recognition is a multiset lookup: we collect all
> summands, sort them,
> and look the signature up in `long_mul_table`. A single summand (xh*yh, a
> cross-sum) matches
> no row, so there's nothing to fold incrementally.
>>
>> Shouldn't we just do a simple matching for the leaf? and then handle
>> that case first and then retry?
>
> The chain is associativity/commutativity-variant. Flatten + sort lets one
> table row cover every shape.
> Matching immediate operands only would push that into a combinatorial set of
> patterns.
>>
>> This has been my biggest concern for even the original patch which is
>> why I wanted to see it split up to see if you could remove it.
>
> We could add a comment to clarify this.
We could limit starts with sth similar to how BB vect limits analyzing
reductions:
/* Should be the chain end. */
&& (!single_imm_use (gimple_assign_lhs (assign),
&use_p, &use_stmt)
|| !is_gimple_assign (use_stmt)
|| (gimple_assign_rhs_code (use_stmt) != code
&& ((code != PLUS_EXPR && code != MINUS_EXPR)
|| (gimple_assign_rhs_code (use_stmt)
!= (code == PLUS_EXPR ? MINUS_EXPR :
PLUS_EXPR))))))
and "discard" irrelevant entries (preserving them, of course).
Richard.
>
> Thanks,
> Konstantinos
>>
>> > + tree t = stack.pop ();
>> > + if (TREE_CODE (t) == SSA_NAME)
>> > + {
>> > + gimple *def = SSA_NAME_DEF_STMT (t);
>> > + if (def
>> > + && is_gimple_assign (def)
>> > + && gimple_assign_rhs_code (def) == outer)
>> > + {
>> > + if (has_single_use (t))
>> > + {
>> > + stack.safe_push (gimple_assign_rhs2 (def));
>> > + stack.safe_push (gimple_assign_rhs1 (def));
>> > + continue;
>> > + }
>> > + if (shared_def_out && !*shared_def_out)
>> > + *shared_def_out = def;
>> > + }
>> > + }
>> > + leaves.safe_push (t);
>> > + if (leaves.length () > LONG_MUL_MAX_SUMMANDS)
>> > + return false;
>> > + }
>> > + return !leaves.is_empty ();
>> > +}
>> > +
>> > +/* If EXPR is defined by LSHIFT_EXPR with a uhwi-valued amount, return
>> > + the shifted input via *INNER_OUT and the amount via *SHIFT_OUT. */
>> > +
>> > +static bool
>> > +long_mul_is_lshift_def (tree expr, tree *inner_out,
>> > + unsigned HOST_WIDE_INT *shift_out)
>> > +{
>> > + if (TREE_CODE (expr) != SSA_NAME)
>> > + return false;
>> > + gimple *def = SSA_NAME_DEF_STMT (expr);
>> > + if (!def || !is_gimple_assign (def)
>> > + || gimple_assign_rhs_code (def) != LSHIFT_EXPR)
>> > + return false;
>> > + tree amount = gimple_assign_rhs2 (def);
>> > + if (!tree_fits_uhwi_p (amount))
>> > + return false;
>> > + *inner_out = gimple_assign_rhs1 (def);
>> > + *shift_out = tree_to_uhwi (amount);
>> > + return true;
>> > +}
>> > +
>> > +/* Fill INFO's kind plus the captures from RES_OPS that the kind requires.
>> > + The kind itself determines how many (op0, op1) and hilo captures to
>> > + pick up from RES_OPS, and whether a baked-in shift is present. */
>> > +
>> > +static void
>> > +long_mul_set_summand (long_mul_summand *info, long_mul_kind kind,
>> > + const tree *res_ops)
>> > +{
>> > + info->kind = kind;
>> > + unsigned n_ops = 0;
>> > + unsigned n_hilos = 0;
>> > + int shift_idx = -1;
>> > + switch (kind)
>> > + {
>> > + case LMK_MUL_HIHI:
>> > + case LMK_MUL_LOLO:
>> > + case LMK_MUL_HILO:
>> > + n_ops = 2;
>> > + break;
>> > + case LMK_CROSS_SUM:
>> > + n_hilos = 2;
>> > + break;
>> > + case LMK_LOW_ACCUM:
>> > + n_ops = 2;
>> > + n_hilos = 2;
>> > + break;
>> > + case LMK_CARRY_CROSS_SUM:
>> > + n_hilos = 3;
>> > + shift_idx = 3;
>> > + break;
>> > + }
>> > + if (n_ops >= 1)
>> > + info->op0 = res_ops[0];
>> > + if (n_ops >= 2)
>> > + info->op1 = res_ops[1];
>> > + if (n_hilos >= 1)
>> > + info->hilo0 = res_ops[n_ops];
>> > + if (n_hilos >= 2)
>> > + info->hilo1 = res_ops[n_ops + 1];
>> > + if (n_hilos >= 3)
>> > + info->hilo2 = res_ops[n_ops + 2];
>> > + if (shift_idx >= 0)
>> > + info->shift = tree_to_uhwi (res_ops[shift_idx]);
>> > +}
>> > +
>> > +/* Classify LEAF as a carry-kind summand. The lshift amount is baked
>> > + into mul_carry_cross_sum, so it's tried before any branch that looks
>> > + for a generic (X >> N) or (X << N) wrapper. */
>> > +
>> > +static bool
>> > +long_mul_classify_carry (tree leaf, long_mul_summand *info)
>> > +{
>> > + tree res_ops[LONG_MUL_MAX_CAPTURES];
>> > + if (gimple_mul_carry_cross_sum (leaf, res_ops, NULL))
>> > + {
>> > + long_mul_set_summand (info, LMK_CARRY_CROSS_SUM, res_ops);
>> > + return true;
>> > + }
>> > + return false;
>> > +}
>> > +
>> > +/* Plus-based summand kinds shared by the (X >> SHIFT) and (X << SHIFT)
>> > + classifiers. */
>> > +
>> > +static bool
>> > +long_mul_classify_plus_kinds (tree inner, long_mul_summand *info)
>> > +{
>> > + tree res_ops[LONG_MUL_MAX_CAPTURES];
>> > + if (gimple_mul_low_accum (inner, res_ops, NULL))
>> > + {
>> > + long_mul_set_summand (info, LMK_LOW_ACCUM, res_ops);
>> > + return true;
>> > + }
>> > + return false;
>> > +}
>> > +
>> > +/* Classify INNER -- already unwrapped from an outer (X >> SHIFT) -- as
>> > + a high-half-extracted summand. mul_hilo (mult-shape) is orthogonal
>> > + to the plus-based kinds and is tried first; mul_cross_sum (any plus)
>> > + is the fallback after the shared plus-based kinds. */
>> > +
>> > +static bool
>> > +long_mul_classify_hi_extract (tree inner, unsigned HOST_WIDE_INT shift,
>> > + long_mul_summand *info)
>> > +{
>> > + tree res_ops[LONG_MUL_MAX_CAPTURES];
>> > + info->extract = LMX_HI;
>> > + info->shift = shift;
>> > + if (gimple_mul_hilo (inner, res_ops, NULL))
>> > + {
>> > + long_mul_set_summand (info, LMK_MUL_HILO, res_ops);
>> > + return true;
>> > + }
>> > + if (long_mul_classify_plus_kinds (inner, info))
>> > + return true;
>> > + if (gimple_mul_cross_sum (inner, res_ops, NULL))
>> > + {
>> > + long_mul_set_summand (info, LMK_CROSS_SUM, res_ops);
>> > + return true;
>> > + }
>> > + return false;
>> > +}
>> > +
>> > +/* Classify INNER -- already unwrapped from an outer (X & MASK) -- as
>> > + a low-half-masked summand. */
>> > +
>> > +static bool
>> > +long_mul_classify_lo_extract (tree inner, unsigned HOST_WIDE_INT mask,
>> > + long_mul_summand *info)
>> > +{
>> > + tree res_ops[LONG_MUL_MAX_CAPTURES];
>> > + info->extract = LMX_LO;
>> > + info->mask = mask;
>> > + if (gimple_mul_lolo (inner, res_ops, NULL))
>> > + {
>> > + long_mul_set_summand (info, LMK_MUL_LOLO, res_ops);
>> > + return true;
>> > + }
>> > + return false;
>> > +}
>> > +
>> > +/* Classify INNER -- already unwrapped from an outer (X << SHIFT) -- as
>> > + a left-shifted summand. No mul_hilo here -- that shape appears only
>> > + under (X >> SHIFT). */
>> > +
>> > +static bool
>> > +long_mul_classify_shl_extract (tree inner, unsigned HOST_WIDE_INT shift,
>> > + long_mul_summand *info)
>> > +{
>> > + tree res_ops[LONG_MUL_MAX_CAPTURES];
>> > + info->extract = LMX_SHL_N;
>> > + info->shift = shift;
>> > + if (long_mul_classify_plus_kinds (inner, info))
>> > + return true;
>> > + if (gimple_mul_cross_sum (inner, res_ops, NULL))
>> > + {
>> > + long_mul_set_summand (info, LMK_CROSS_SUM, res_ops);
>> > + return true;
>> > + }
>> > + return false;
>> > +}
>> > +
>> > +/* Classify LEAF as one of the bare-kind summands (no extraction
>> > + wrapper): mul_hihi or mul_lolo standing on their own. */
>> > +
>> > +static bool
>> > +long_mul_classify_bare (tree leaf, long_mul_summand *info)
>> > +{
>> > + tree res_ops[LONG_MUL_MAX_CAPTURES];
>> > + if (gimple_mul_hihi (leaf, res_ops, NULL))
>> > + {
>> > + long_mul_set_summand (info, LMK_MUL_HIHI, res_ops);
>> > + return true;
>> > + }
>> > + if (gimple_mul_lolo (leaf, res_ops, NULL))
>> > + {
>> > + long_mul_set_summand (info, LMK_MUL_LOLO, res_ops);
>> > + return true;
>> > + }
>> > + return false;
>> > +}
>> > +
>> > +/* Classify LEAF as one of the long-multiply summand shapes. On success,
>> > + fill *INFO with the kind, extract, captured operands and shift/mask.
>> > + Dispatches to per-extract helpers; the order matters because the
>> > + carry kinds bake an lshift into the pattern and would otherwise be
>> > + misread by the (X << N) branch. */
>> > +
>> > +static bool
>> > +long_mul_classify_summand (tree leaf, long_mul_summand *info)
>> > +{
>> > + tree res_ops[LONG_MUL_MAX_CAPTURES];
>> > + *info = {};
>> > +
>> > + if (long_mul_classify_carry (leaf, info))
>> > + return true;
>> > +
>> > + if (gimple_mul_hi (leaf, res_ops, NULL))
>> > + return long_mul_classify_hi_extract (res_ops[0],
>> > + tree_to_uhwi (res_ops[1]), info);
>> > +
>> > + if (gimple_mul_lo (leaf, res_ops, NULL))
>> > + return long_mul_classify_lo_extract (res_ops[0],
>> > + tree_to_uhwi (res_ops[1]), info);
>> > +
>> > + tree inner;
>> > + unsigned HOST_WIDE_INT shift;
>> > + if (long_mul_is_lshift_def (leaf, &inner, &shift))
>> > + return long_mul_classify_shl_extract (inner, shift, info);
>> > +
>> > + return long_mul_classify_bare (leaf, info);
>> > +}
>> > +
>> > +/* qsort comparator: sort summands by (kind, extract) to put a multiset
>> > + into canonical order for table lookup. Unstable sort within a tie is
>> > + harmless: no row in long_mul_table pairs distinct subterms under the
>> > + same (kind, extract), and long_mul_check_consistency cross-validates
>> > + that matching summands share one canonical (op0, op1). */
>> > +
>> > +static int
>> > +long_mul_summand_compare (const void *a, const void *b)
>> > +{
>> > + const long_mul_summand *sa = (const long_mul_summand *) a;
>> > + const long_mul_summand *sb = (const long_mul_summand *) b;
>> > + if (sa->kind != sb->kind)
>> > + return (int) sa->kind - (int) sb->kind;
>> > + return (int) sa->extract - (int) sb->extract;
>> > +}
>> > +
>> > +/* One row of the long-multiply variant table. COUNT is how many entries
>> > + of SIG carry the row's signature (2 to LONG_MUL_MAX_SUMMANDS); a row
>> > + with fewer summands leaves the remaining SIG entries zero-initialized.
>> > + Those zeros are not a terminator -- {LMK_MUL_HIHI, LMX_NONE} is itself
>> > a
>> > + valid signature -- so long_mul_signature_matches is bounded by COUNT,
>> > + never by a sentinel entry. */
>> > +
>> > +struct long_mul_row {
>> > + enum long_mul_row_part { HIGH_PART, LOW_PART } part;
>> > + tree_code outer;
>> > + unsigned char count;
>> > + struct {
>> > + long_mul_kind kind;
>> > + long_mul_extract extract;
>> > + } sig[LONG_MUL_MAX_SUMMANDS];
>> > + bool (*extra_check) (const vec<long_mul_summand> &, gimple *);
>> > +};
>> > +
>> > +/* True if (A, B) is the same pair as (OP0, OP1) in either order. */
>> > +
>> > +static inline bool
>> > +long_mul_same_ops (tree a, tree b, tree op0, tree op1)
>> > +{
>> > + return (a == op0 && b == op1) || (a == op1 && b == op0);
>> > +}
>> > +
>> > +/* True if H is a cross-half product of (OP0, OP1) -- gimple_mul_hilo
>> > + recognizes it and its captured operands match the pair. */
>> > +
>> > +static bool
>> > +long_mul_is_cross_half (tree h, tree op0, tree op1)
>> > +{
>> > + tree scratch[LONG_MUL_MAX_CAPTURES];
>> > + return gimple_mul_hilo (h, scratch, NULL)
>> > + && long_mul_same_ops (scratch[0], scratch[1], op0, op1);
>> > +}
>> > +
>> > +/* Orientation of the mul_hilo capture H relative to (OP0, OP1):
>> > + returns 0 for high(OP0)*low(OP1), 1 for high(OP1)*low(OP0), or -1
>> > + if H does not decompose that way. A cross-sum of two mul_hilos must
>> > + see one of each orientation -- otherwise a doubled factor would fold
>> > + to the wrong value. (In a self-multiply the two orientations
>> > + coincide; see the OP0 == OP1 bypass in long_mul_check_consistency.) */
>> > +
>> > +static int
>> > +long_mul_hilo_orientation (tree h, tree op0, tree op1)
>> > +{
>> > + tree scratch[LONG_MUL_MAX_CAPTURES];
>> > + if (!gimple_mul_hilo (h, scratch, NULL))
>> > + return -1;
>> > + if (scratch[0] == op0 && scratch[1] == op1)
>> > + return 0;
>> > + if (scratch[0] == op1 && scratch[1] == op0)
>> > + return 1;
>> > + return -1;
>> > +}
>> > +
>> > +/* Find the first summand that carries operand captures, and return its
>> > + (op0, op1) pair in *OP0_OUT / *OP1_OUT. Returns false if no summand
>> > + provides them. */
>> > +
>> > +static bool
>> > +long_mul_canonical_ops (const vec<long_mul_summand> &summands,
>> > + tree *op0_out, tree *op1_out)
>> > +{
>> > + for (const long_mul_summand &s : summands)
>> > + if (s.op0)
>> > + {
>> > + *op0_out = s.op0;
>> > + *op1_out = s.op1;
>> > + return true;
>> > + }
>> > + return false;
>> > +}
>> > +
>> > +/* Run the cross-summand validation invariants and return the canonical
>> > + (op0, op1). Returns false unless all summands that carry operands use
>> > + the same (op0, op1) pair (in either order), every LMX_HI/LMX_SHL_N
>> > shift
>> > + equals halfwidth, every captured hilo is a true cross-half product of
>> > + (op0, op1), and every cross-half pair (both those inside a single
>> > + mul_cross_sum-bearing summand and those spread across separate
>> > + LMK_MUL_HILO summands) contains one of each orientation. */
>> > +
>> > +static bool
>> > +long_mul_check_consistency (const vec<long_mul_summand> &summands,
>> > + tree *op0_out, tree *op1_out)
>> > +{
>> > + tree op0, op1;
>> > + if (!long_mul_canonical_ops (summands, &op0, &op1))
>> > + return false;
>> > +
>> > + tree op_type = TREE_TYPE (op0);
>> > + if (!INTEGRAL_TYPE_P (op_type)
>> > + || TYPE_PRECISION (op_type) % 2 != 0)
>> > + return false;
>> > + unsigned int halfwidth = TYPE_PRECISION (op_type) / 2;
>> > +
>> > + /* Self-multiply (x*x) collapses the two cross-halves onto one value,
>> > + so the complementarity constraint is a trivial no-op there. */
>> > + bool need_orient = op0 != op1;
>> > + int mul_hilo_orient[2] = { 0, 0 };
>> > +
>> > + for (const long_mul_summand &s : summands)
>> > + {
>> > + if (s.op0 && !long_mul_same_ops (s.op0, s.op1, op0, op1))
>> > + return false;
>> > + if ((s.extract == LMX_HI || s.extract == LMX_SHL_N)
>> > + && s.shift != halfwidth)
>> > + return false;
>> > + tree hilos[3] = { s.hilo0, s.hilo1, s.hilo2 };
>> > + for (tree h : hilos)
>> > + if (h && !long_mul_is_cross_half (h, op0, op1))
>> > + return false;
>> > +
>> > + if (!need_orient)
>> > + continue;
>> > +
>> > + /* The two cross-sum operands are the last two non-null hilos:
>> > + (hilo1, hilo2) for the CARRY_*_SUM kinds, (hilo0, hilo1) for
>> > + the CROSS_SUM / SUM / ACCUM / LADDER_SUM kinds, none for the
>> > + rest. */
>> > + tree a = NULL_TREE;
>> > + tree b = NULL_TREE;
>> > + if (s.hilo2)
>> > + {
>> > + a = s.hilo1;
>> > + b = s.hilo2;
>> > + }
>> > + else if (s.hilo1)
>> > + {
>> > + a = s.hilo0;
>> > + b = s.hilo1;
>> > + }
>> > + if (a && b
>> > + && (long_mul_hilo_orientation (a, op0, op1)
>> > + == long_mul_hilo_orientation (b, op0, op1)))
>> > + return false;
>> > +
>> > + /* Two LMK_MUL_HILO summands (the two-hilos ladder form) stand for
>> > + the two cross-halves separately; count orientations and require
>> > + the pair to be complementary. s.op0/op1 is already validated to
>> > + match (op0, op1) in some order above. */
>> > + if (s.kind == LMK_MUL_HILO && s.op0)
>> > + mul_hilo_orient[s.op0 == op1]++;
>> > + }
>> > +
>> > + if (mul_hilo_orient[0] + mul_hilo_orient[1] >= 2
>> > + && (mul_hilo_orient[0] == 0 || mul_hilo_orient[1] == 0))
>> > + return false;
>> > +
>> > + *op0_out = op0;
>> > + *op1_out = op1;
>> > + return true;
>> > +}
>> > +
>> > +/* Compare the (already-sorted) SUMMANDS multiset against ROW.sig. */
>> > +
>> > +static bool
>> > +long_mul_signature_matches (const vec<long_mul_summand> &summands,
>> > + const long_mul_row &row)
>> > +{
>> > + if (row.count != summands.length ())
>> > + return false;
>> > + for (unsigned i = 0; i < row.count; i++)
>> > + if (summands[i].kind != row.sig[i].kind
>> > + || summands[i].extract != row.sig[i].extract)
>> > + return false;
>> > + return true;
>> > +}
>> > +
>> > +/* Long-multiply variant table. Each row enumerates the multiset of
>> > + (kind, extract) summands that compose one long-multiply form. Rows
>> > + are sorted by long_mul_summand_compare, matching the input summands'
>> > + sort order, so a plain element-wise compare suffices. Rows describe
>> > + unsigned schoolbook expansions on an even-width 2N-bit type split at
>> > + half-width N; EXTRA_CHECK carries invariants the (kind, extract)
>> > + signature cannot express. */
>> > +
>> > +static const long_mul_row long_mul_table[] = {
>> > + /* HIGH-PART fold. Notation: xh, xl, yh, yl are the half-width pieces
>> > + of x and y; N is the half-width. cross_sum = xh*yl + xl*yh; hilo is
>> > + either xh*yl or xl*yh (consumers validate the operand shape). */
>> > + /* xh*yh + (low_accum >> N) + (cross_sum >> N)
>> > + + ((hilo > cross_sum) << N),
>> > + low_accum = (xl*yl >> N) + (cross_sum & mask). */
>> > + { long_mul_row::HIGH_PART, PLUS_EXPR, 4,
>> > + { { LMK_MUL_HIHI, LMX_NONE },
>> > + { LMK_CROSS_SUM, LMX_HI },
>> > + { LMK_LOW_ACCUM, LMX_HI },
>> > + { LMK_CARRY_CROSS_SUM, LMX_NONE } },
>> > + NULL },
>> > + /* LOW-PART fold. Recover the lower 2N bits from xl*yl plus a
>> > + shifted cross-half term. Notation as for the HIGH-PART row above.
>> > */
>> > + /* (xl*yl & mask) | (low_accum << N),
>> > + low_accum = (xl*yl >> N) + (cross_sum & mask). */
>> > + { long_mul_row::LOW_PART, BIT_IOR_EXPR, 2,
>> > + { { LMK_MUL_LOLO, LMX_LO },
>> > + { LMK_LOW_ACCUM, LMX_SHL_N } },
>> > + NULL },
>> > +};
>> > +
>> > +/* If a multi-used inner addition (sharing the chain's outer code) blocked
>> > + linearization of a long-mul candidate, emit a dump-file hint pointing
>> > + at it. */
>> > +
>> > +static void
>> > +long_mul_hint_shared_intermediate (gimple *shared_def)
>> > +{
>> > + if (!shared_def || !dump_file || !(dump_flags & TDF_DETAILS))
>> > + return;
>> > + fprintf (dump_file, "long-mul fold rejected: shared intermediate at ");
>> > + print_gimple_stmt (dump_file, shared_def, 0, TDF_SLIM);
>> > +}
>> > +
>> > +/* Top-level entry for long-multiply folding. Walks STMT's outer
>> > + addition or BIT_IOR chain, classifies the summands, and dispatches
>> > + to create_mul_high_seq / create_mul_low_seq if the multiset matches
>> > + a known long-multiply form. Returns true on success. */
>> > +
>> > +static bool
>> > +match_long_mul (gimple *stmt)
>> > +{
>> > + if (!is_gimple_assign (stmt))
>> > + return false;
>> > + tree_code outer = gimple_assign_rhs_code (stmt);
>> > + if (outer != PLUS_EXPR && outer != BIT_IOR_EXPR)
>> > + return false;
>> > +
>> > + /* Skip non-candidate adds (signed, pointer, odd-width) before walking
>> > the
>> > + chain. No legitimate long-mul leaf has a type the atoms would
>> > reject;
>> > + this just avoids the linearize/classify work on every other
>> > PLUS/IOR. */
>> > + tree lhs_type = TREE_TYPE (gimple_get_lhs (stmt));
>> > + if (!INTEGRAL_TYPE_P (lhs_type)
>> > + || !TYPE_UNSIGNED (lhs_type)
>> > + || TYPE_PRECISION (lhs_type) % 2 != 0)
>> > + return false;
>> > +
>> > + auto_vec<tree, LONG_MUL_MAX_SUMMANDS + 1> leaves;
>> > + gimple *shared_def = NULL;
>> > + if (!long_mul_linearize_chain (stmt, outer, leaves, &shared_def))
>> > + return false;
>> > + if (leaves.length () < 2)
>> > + return false;
>> > +
>> > + auto_vec<long_mul_summand, LONG_MUL_MAX_SUMMANDS> summands;
>> > + for (tree leaf : leaves)
>> > + {
>> > + long_mul_summand s;
>> > + if (!long_mul_classify_summand (leaf, &s))
>> > + {
>> > + long_mul_hint_shared_intermediate (shared_def);
>> > + return false;
>> > + }
>> > + summands.quick_push (s);
>> > + }
>> > + summands.qsort (long_mul_summand_compare);
>> > +
>> > + /* HIGH_PART rows emit a 2N-bit multiply that is consumed by
>> > + pass_optimize_widening_mul (WIDEN_MULT_EXPR conversion or
>> > + longhand re-synthesis) or by expand (supported 2N mode);
>> > + LOW_PART rows emit a plain MULT_EXPR. Emission needs only a 2N
>> > + mode to exist in the mode table -- capability is settled on the
>> > + lowering side. */
>> > + scalar_int_mode mode, wide_mode;
>> > + bool can_emit_high
>> > + = is_a <scalar_int_mode> (TYPE_MODE (lhs_type), &mode)
>> > + && GET_MODE_2XWIDER_MODE (mode).exists (&wide_mode);
>> > +
>> > + for (const long_mul_row &row : long_mul_table)
>> > + {
>> > + if (row.outer != outer
>> > + || (row.part == long_mul_row::HIGH_PART && !can_emit_high)
>> > + || !long_mul_signature_matches (summands, row))
>> > + continue;
>> > +
>> > + tree op0, op1;
>> > + if (!long_mul_check_consistency (summands, &op0, &op1))
>> > + continue;
>> > +
>> > + /* Do not emit the wide chain when an operand is subject to
>> > + abnormal coalescing: the widening_mul-side consumers refuse
>> > + such operands (see convert_mult_to_widen), which would leave
>> > + the chain without a consumer. */
>> > + if (row.part == long_mul_row::HIGH_PART
>> > + && ((TREE_CODE (op0) == SSA_NAME
>> > + && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0))
>> > + || (TREE_CODE (op1) == SSA_NAME
>> > + && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op1))))
>> > + continue;
>> > +
>> > + if (row.extra_check && !row.extra_check (summands, stmt))
>> > + continue;
>> > +
>> > + if (row.part == long_mul_row::HIGH_PART)
>> > + {
>> > + create_mul_high_seq (op0, op1, stmt);
>> > + if (dump_file && (dump_flags & TDF_DETAILS))
>> > + fprintf (dump_file, "Long multiplication high part folded.\n");
>> > + return true;
>> > + }
>> > + create_mul_low_seq (op0, op1, stmt);
>> > + if (dump_file && (dump_flags & TDF_DETAILS))
>> > + fprintf (dump_file, "Long multiplication low part folded.\n");
>> > + return true;
>> > + }
>> > +
>> > + long_mul_hint_shared_intermediate (shared_def);
>> > + return false;
>> > +}
>> >
>> > /* Determine whether applying the 2 permutations (mask1 then mask2)
>> > gives back one of the input. */
>> > @@ -5851,11 +6538,15 @@ pass_forwprop::execute (function *fun)
>> > }
>> > else if (TREE_CODE_CLASS (code) == tcc_comparison)
>> > changed |= forward_propagate_into_comparison (&gsi);
>> > - else if ((code == PLUS_EXPR
>> > - || code == BIT_IOR_EXPR
>> > - || code == BIT_XOR_EXPR)
>> > - && simplify_rotate (&gsi))
>> > - changed = true;
>> > + else if ((code == PLUS_EXPR || code == BIT_IOR_EXPR))
>> > + {
>> > + bool folded = match_long_mul (stmt);
>> > + if (!folded)
>> > + folded = simplify_rotate (&gsi);
>> > + changed |= folded;
>> > + }
>> > + else if (code == BIT_XOR_EXPR)
>> > + changed |= simplify_rotate (&gsi);
>> > else if (code == VEC_PERM_EXPR)
>> > changed |= simplify_permutation (&gsi);
>> > else if (code == CONSTRUCTOR
>> > --
>> > 2.55.0
>> >
