On Fri, Jun 17, 2022 at 10:57 AM Arjun Shankar <ar...@redhat.com> wrote: > > Expressions of the form "X + CST < Y + CST" where: > > * CST is an unsigned integer constant with only the MSB set, and > * X and Y's types have integer conversion ranks <= CST's > > can be simplified to "(signed) X < (signed) Y". > > This is because, assuming a 32-bit signed numbers, > (unsigned) INT_MIN + 0x80000000 is 0, and > (unsigned) INT_MAX + 0x80000000 is UINT_MAX. > > i.e. the result increases monotonically with signed input. > > This means: > ((signed) X < (signed) Y) iff (X + 0x80000000 < Y + 0x80000000) > > gcc/ > * match.pd (X + C < Y + C -> (signed) X < (signed) Y, if C is > 0x80000000): New simplification. > gcc/testsuite/ > * gcc.dg/pr94899.c: New test. > --- > gcc/match.pd | 13 +++++++++ > gcc/testsuite/gcc.dg/pr94899.c | 48 ++++++++++++++++++++++++++++++++++ > 2 files changed, 61 insertions(+) > create mode 100644 gcc/testsuite/gcc.dg/pr94899.c > --- > v2: https://gcc.gnu.org/pipermail/gcc-patches/2022-February/589709.html > > Notes on v3, based on Richard and Jakub's review comments: > > 1. Canonicalized the match expression to avoid having to use ":c". > 2. Redefined MAGIC in the test to avoid running afoul of 16-bit int > machines. > > Richard has approved this patch for inclusion in GCC 13: > https://gcc.gnu.org/pipermail/gcc-patches/2022-February/589852.html > > diff --git a/gcc/match.pd b/gcc/match.pd > index 3e9572e4c9c..ef42611854a 100644 > --- a/gcc/match.pd > +++ b/gcc/match.pd > @@ -2080,6 +2080,19 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0)) > && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0))) > (op @0 @1)))) > + > +/* As a special case, X + C < Y + C is the same as (signed) X < (signed) Y > + when C is an unsigned integer constant with only the MSB set, and X and > + Y have types of equal or lower integer conversion rank than C's. */ > +(for op (lt le ge gt) > + (simplify > + (op (plus @1 INTEGER_CST@0) (plus @2 INTEGER_CST@0)) > + (if (INTEGRAL_TYPE_P (TREE_TYPE (@0)) > + && TYPE_UNSIGNED (TREE_TYPE (@0)) > + && wi::only_sign_bit_p (wi::to_wide (@0))) > + (with { tree stype = signed_type_for (TREE_TYPE (@0)); } > + (op (convert:stype @1) (convert:stype @2)))))) > + > /* For equality and subtraction, this is also true with wrapping overflow. > */ > (for op (eq ne minus) > (simplify > diff --git a/gcc/testsuite/gcc.dg/pr94899.c b/gcc/testsuite/gcc.dg/pr94899.c > new file mode 100644 > index 00000000000..685201307ec > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/pr94899.c > @@ -0,0 +1,48 @@ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fdump-tree-optimized" } */ > + > +typedef __INT16_TYPE__ int16_t; > +typedef __INT32_TYPE__ int32_t; > +typedef __UINT16_TYPE__ uint16_t; > +typedef __UINT32_TYPE__ uint32_t; > + > +#define MAGIC (~ (uint32_t) 0 / 2 + 1) > + > +int > +f_i16_i16 (int16_t x, int16_t y) > +{ > + return x + MAGIC < y + MAGIC; > +} > + > +int > +f_i16_i32 (int16_t x, int32_t y) > +{ > + return x + MAGIC < y + MAGIC; > +} > + > +int > +f_i32_i32 (int32_t x, int32_t y) > +{ > + return x + MAGIC < y + MAGIC; > +} > + > +int > +f_u32_i32 (uint32_t x, int32_t y) > +{ > + return x + MAGIC < y + MAGIC; > +} > + > +int > +f_u32_u32 (uint32_t x, uint32_t y) > +{ > + return x + MAGIC < y + MAGIC; > +} > + > +int > +f_i32_i32_sub (int32_t x, int32_t y) > +{ > + return x - MAGIC < y - MAGIC; > +} > + > +/* The constants above should have been optimized away. */ > +/* { dg-final { scan-tree-dump-times "2147483648" 0 "optimized"} } */
It might be possible to test for zero + or - operations instead? OK otherwise. Thanks, Richard. > -- > 2.35.3 >
