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From: Jakub Jelinek <jakub@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-1187] match.pd: Remove "+ 0x80000000" in int comparisons [PR94899] Date: Tue, 21 Jun 2022 10:22:14 +0000 (GMT) [thread overview] Message-ID: <20220621102214.B42AD3857B8F@sourceware.org> (raw) https://gcc.gnu.org/g:ab981aab92cbc71918fbaadcf6fa64bdb2b69be7 commit r13-1187-gab981aab92cbc71918fbaadcf6fa64bdb2b69be7 Author: Arjun Shankar <arjun@redhat.com> Date: Tue Jun 21 12:12:11 2022 +0200 match.pd: Remove "+ 0x80000000" in int comparisons [PR94899] 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/ PR tree-optimization/94899 * match.pd (X + C < Y + C -> (signed) X < (signed) Y, if C is 0x80000000): New simplification. gcc/testsuite/ * gcc.dg/pr94899.c: New test. Diff: --- gcc/match.pd | 13 +++++++++++ gcc/testsuite/gcc.dg/pr94899.c | 49 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 62 insertions(+) diff --git a/gcc/match.pd b/gcc/match.pd index a63b649841b..4a570894b2e 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -2089,6 +2089,19 @@ 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 @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..9fad057e4d2 --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr94899.c @@ -0,0 +1,49 @@ +/* { 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 addition/subtraction of constants should be optimized away. */ +/* { dg-final { scan-tree-dump-not " \\+ " "optimized"} } */ +/* { dg-final { scan-tree-dump-not " \\- " "optimized"} } */
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