Comparisons between memory and constants might be done in a smaller mode
resulting in smaller constants which might finally end up as immediates
instead of in the literal pool.
For example, on s390x a non-symmetric comparison like
x <= 0x3fffffffffffffff
results in the constant being spilled to the literal pool and an 8 byte
memory comparison is emitted. Ideally, an equivalent comparison
x0 <= 0x3f
where x0 is the most significant byte of x, is emitted where the
constant is smaller and more likely to materialize as an immediate.
Similarly, comparisons of the form
x >= 0x4000000000000000
can be shortened into x0 >= 0x40.
I'm not entirely sure whether combine is the right place to implement
something like this. In my first try I implemented it in
TARGET_CANONICALIZE_COMPARISON but then thought other targets might
profit from it, too. simplify_context::simplify_relational_operation_1
seems to be the wrong place since code/mode may change. Any opinions?
gcc/ChangeLog:
* combine.cc (simplify_compare_const): Narrow comparison of
memory and constant.
(try_combine): Adapt new function signature.
(simplify_comparison): Adapt new function signature.
gcc/testsuite/ChangeLog:
* gcc.target/s390/cmp-mem-const-1.c: New test.
* gcc.target/s390/cmp-mem-const-2.c: New test.
---
gcc/combine.cc | 82 ++++++++++++++-
.../gcc.target/s390/cmp-mem-const-1.c | 99 +++++++++++++++++++
.../gcc.target/s390/cmp-mem-const-2.c | 23 +++++
3 files changed, 200 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
create mode 100644 gcc/testsuite/gcc.target/s390/cmp-mem-const-2.c
diff --git a/gcc/combine.cc b/gcc/combine.cc
index 5aa0ec5c45a..6ad1600dc1b 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -460,7 +460,7 @@ static rtx simplify_shift_const (rtx, enum rtx_code,
machine_mode, rtx,
static int recog_for_combine (rtx *, rtx_insn *, rtx *);
static rtx gen_lowpart_for_combine (machine_mode, rtx);
static enum rtx_code simplify_compare_const (enum rtx_code, machine_mode,
- rtx, rtx *);
+ rtx *, rtx *);
static enum rtx_code simplify_comparison (enum rtx_code, rtx *, rtx *);
static void update_table_tick (rtx);
static void record_value_for_reg (rtx, rtx_insn *, rtx);
@@ -3185,7 +3185,7 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1,
rtx_insn *i0,
compare_code = orig_compare_code = GET_CODE (*cc_use_loc);
if (is_a <scalar_int_mode> (GET_MODE (i2dest), &mode))
compare_code = simplify_compare_const (compare_code, mode,
- op0, &op1);
+ &op0, &op1);
target_canonicalize_comparison (&compare_code, &op0, &op1, 1);
}
@@ -11800,9 +11800,10 @@ gen_lowpart_for_combine (machine_mode omode, rtx x)
static enum rtx_code
simplify_compare_const (enum rtx_code code, machine_mode mode,
- rtx op0, rtx *pop1)
+ rtx *pop0, rtx *pop1)
{
scalar_int_mode int_mode;
+ rtx op0 = *pop0;
HOST_WIDE_INT const_op = INTVAL (*pop1);
/* Get the constant we are comparing against and turn off all bits
@@ -11987,6 +11988,79 @@ simplify_compare_const (enum rtx_code code,
machine_mode mode,
break;
}
+ /* Narrow non-symmetric comparison of memory and constant as e.g.
+ x0...x7 <= 0x3fffffffffffffff into x0 <= 0x3f where x0 is the most
+ significant byte. Likewise, transform x0...x7 >= 0x4000000000000000 into
+ x0 >= 0x40. */
+ if ((code == LEU || code == LTU || code == GEU || code == GTU)
+ && is_a <scalar_int_mode> (GET_MODE (op0), &int_mode)
+ && MEM_P (op0)
+ && !MEM_VOLATILE_P (op0)
+ && (unsigned HOST_WIDE_INT)const_op > 0xff)
+ {
+ unsigned HOST_WIDE_INT n = (unsigned HOST_WIDE_INT)const_op;
+ enum rtx_code adjusted_code = code;
+
+ /* If the least significant bit is already zero, then adjust the
+ comparison in the hope that we hit cases like
+ op0 <= 0x3ffffdfffffffffe
+ where the adjusted comparison
+ op0 < 0x3ffffdffffffffff
+ can be shortened into
+ op0' < 0x3ffffd. */
+ if (code == LEU && (n & 1) == 0)
+ {
+ ++n;
+ adjusted_code = LTU;
+ }
+ /* or e.g. op0 < 0x4020000000000000 */
+ else if (code == LTU && (n & 1) == 0)
+ {
+ --n;
+ adjusted_code = LEU;
+ }
+ /* or op0 >= 0x4000000000000001 */
+ else if (code == GEU && (n & 1) == 1)
+ {
+ --n;
+ adjusted_code = GTU;
+ }
+ /* or op0 > 0x3fffffffffffffff. */
+ else if (code == GTU && (n & 1) == 1)
+ {
+ ++n;
+ adjusted_code = GEU;
+ }
+
+ scalar_int_mode narrow_mode_iter;
+ bool lower_p = code == LEU || code == LTU;
+ bool greater_p = !lower_p;
+ FOR_EACH_MODE_UNTIL (narrow_mode_iter, int_mode)
+ {
+ unsigned nbits = GET_MODE_PRECISION (int_mode)
+ - GET_MODE_PRECISION (narrow_mode_iter);
+ unsigned HOST_WIDE_INT mask = (HOST_WIDE_INT_1U << nbits) - 1;
+ unsigned HOST_WIDE_INT lower_bits = n & mask;
+ if ((lower_p && lower_bits == mask)
+ || (greater_p && lower_bits == 0))
+ {
+ n >>= nbits;
+ break;
+ }
+ }
+
+ if (narrow_mode_iter < int_mode)
+ {
+ poly_int64 offset = BYTES_BIG_ENDIAN
+ ? 0
+ : GET_MODE_SIZE (int_mode)
+ - GET_MODE_SIZE (narrow_mode_iter);
+ *pop0 = adjust_address (op0, narrow_mode_iter, offset);
+ *pop1 = GEN_INT (n);
+ return adjusted_code;
+ }
+ }
+
*pop1 = GEN_INT (const_op);
return code;
}
@@ -12179,7 +12253,7 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx
*pop1)
/* Try to simplify the compare to constant, possibly changing the
comparison op, and/or changing op1 to zero. */
- code = simplify_compare_const (code, raw_mode, op0, &op1);
+ code = simplify_compare_const (code, raw_mode, &op0, &op1);
const_op = INTVAL (op1);
/* Compute some predicates to simplify code below. */
diff --git a/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
b/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
new file mode 100644
index 00000000000..b90c2a8c224
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
@@ -0,0 +1,99 @@
+/* { dg-do compile { target { lp64 } } } */
+/* { dg-options "-O1 -march=z13 -mzarch" } */
+/* { dg-final { scan-assembler-not {\tclc\t} } } */
+
+int
+ge_8b (unsigned long *x)
+{
+ return *x >= 0x4000000000000000;
+}
+
+int
+ge_8b_adjust (unsigned long *x)
+{
+ return *x >= 0x4000000000000001;
+}
+
+int
+ge_6b (unsigned long *x)
+{
+ return *x >= 0x400000000000;
+}
+
+int
+ge_6b_adjust (unsigned long *x)
+{
+ return *x >= 0x400000000001;
+}
+
+int
+gt_8b (unsigned long *x)
+{
+ return *x > 0x4000000000000000;
+}
+
+int
+gt_8b_adjust (unsigned long *x)
+{
+ return *x > 0x3fffffffffffffff;
+}
+
+int
+gt_6b (unsigned long *x)
+{
+ return *x > 0x400000000000;
+}
+
+int
+gt_6b_adjust (unsigned long *x)
+{
+ return *x > 0x3fffffffffff;
+}
+
+int
+le_8b (unsigned long *x)
+{
+ return *x <= 0x3ff7ffffffffffff;
+}
+
+int
+le_6b (unsigned long *x)
+{
+ return *x <= 0x3f7fffffffff;
+}
+
+int
+le_8b_adjust (unsigned long *x)
+{
+ return *x <= 0x3ffffdfffffffffe;
+}
+
+int
+le_6b_adjust (unsigned long *x)
+{
+ return *x <= 0x3ffffffffffe;
+}
+
+int
+lt_8b (unsigned long *x)
+{
+ return *x < 0x3fffffffffffffff;
+}
+
+int
+lt_6b (unsigned long *x)
+{
+ return *x < 0x3fffffffffff;
+}
+
+int
+lt_8b_adjust (unsigned long *x)
+{
+ return *x < 0x4020000000000000;
+}
+
+int
+lt_6b_adjust (unsigned long *x)
+{
+ return *x < 0x400000000000;
+}
diff --git a/gcc/testsuite/gcc.target/s390/cmp-mem-const-2.c
b/gcc/testsuite/gcc.target/s390/cmp-mem-const-2.c
new file mode 100644
index 00000000000..e3951870d94
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/cmp-mem-const-2.c
@@ -0,0 +1,23 @@
+/* { dg-do compile { target { lp64 } } } */
+/* { dg-options "-O1 -march=z13 -mzarch" } */
+/* { dg-final { scan-assembler-not {\tclc\t} } } */
+
+struct s
+{
+ long a;
+ unsigned b : 1;
+ unsigned c : 1;
+};
+
+int foo (struct s *x)
+{
+ /* Expression
+ x->b || x->c
+ is transformed into
+ _1 = BIT_FIELD_REF <*x_4(D), 64, 64>;
+ _2 = _1 > 0x3FFFFFFFFFFFFFFF;
+ where the constant may materialize in the literal pool and an 8 byte CLC
+ may be emitted. Ensure this is not the case.
+ */
+ return x->b || x->c;
+}
--
2.39.2
