https://gcc.gnu.org/g:3c378398111f7fc3c026b705e3ac088b27d4c307
commit r16-5611-g3c378398111f7fc3c026b705e3ac088b27d4c307 Author: Dhruv Chawla <[email protected]> Date: Wed Jul 23 01:41:51 2025 -0700 Make better use of overflowing operations in max/min(a, add/sub(a, b)) [PR116815] This patch folds the following patterns: - For add: - umax (a, add (a, b)) -> [sum, ovf] = adds (a, b); !ovf ? sum : a - umin (a, add (a, b)) -> [sum, ovf] = adds (a, b); !ovf ? a : sum ... along with the commutated versions: - umax (a, add (b, a)) -> [sum, ovf] = adds (b, a); !ovf ? sum : a - umin (a, add (b, a)) -> [sum, ovf] = adds (b, a); !ovf ? a : sum - For sub: - umax (a, sub (a, b)) -> [diff, udf] = subs (a, b); udf ? diff : a - umin (a, sub (a, b)) -> [diff, udf] = subs (a, b); udf ? a : diff Where ovf is the overflow flag and udf is the underflow flag. adds and subs are generated by generating parallel compare+plus/minus which map to add<mode>3_compareC and sub<mode>3_compare1. This patch is a respin of the patch posted at https://gcc.gnu.org/pipermail/gcc-patches/2025-May/685021.html as per the suggestion to turn it into a target-specific transform by Richard Biener. FIXME: This pattern cannot currently factor multiple occurences of the add expression into a single adds, eg: max (a, a + b) + min (a + b, b) ends up generating two adds instructions. This is something that was lost when going from GIMPLE to target-specific transforms. Bootstrapped and regtested on aarch64-unknown-linux-gnu. Signed-off-by: Dhruv Chawla <[email protected]> PR middle-end/116815 gcc/ChangeLog: * config/aarch64/aarch64.md (*aarch64_plus_within_<optab><mode>3_<ovf_commutate>): New pattern. (*aarch64_minus_within_<optab><mode>3): Likewise. * config/aarch64/iterators.md (ovf_add_cmp): New code attribute. (udf_sub_cmp): Likewise. (UMAXMIN): New code iterator. (ovf_commutate): New iterator. (ovf_comm_opp): New int attribute. gcc/testsuite/ChangeLog: * gcc.target/aarch64/pr116815-1.c: New test. * gcc.target/aarch64/pr116815-2.c: Likewise. * gcc.target/aarch64/pr116815-3.c: Likewise. Diff: --- gcc/config/aarch64/aarch64.md | 60 +++++++++++++ gcc/config/aarch64/iterators.md | 9 ++ gcc/testsuite/gcc.target/aarch64/pr116815-1.c | 120 ++++++++++++++++++++++++++ gcc/testsuite/gcc.target/aarch64/pr116815-2.c | 44 ++++++++++ gcc/testsuite/gcc.target/aarch64/pr116815-3.c | 60 +++++++++++++ 5 files changed, 293 insertions(+) diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md index de6b1d0ed06b..8dcb5e3f0ecb 100644 --- a/gcc/config/aarch64/aarch64.md +++ b/gcc/config/aarch64/aarch64.md @@ -4482,6 +4482,66 @@ [(set_attr "type" "<su>div")] ) +;; umax (a, add (a, b)) => [sum, ovf] = adds (a, b); !ovf ? sum : a +;; umin (a, add (a, b)) => [sum, ovf] = adds (a, b); !ovf ? a : sum +;; ... and the commutated versions: +;; umax (a, add (b, a)) => [sum, ovf] = adds (b, a); !ovf ? sum : a +;; umin (a, add (b, a)) => [sum, ovf] = adds (b, a); !ovf ? a : sum +(define_insn_and_split "*aarch64_plus_within_<optab><mode>3_<ovf_commutate>" + [(set (match_operand:GPI 0 "register_operand" "=r") + (UMAXMIN:GPI + (plus:GPI (match_operand:GPI 1 "register_operand" "r") + (match_operand:GPI 2 "register_operand" "r")) + (match_dup ovf_commutate))) + (clobber (match_scratch:GPI 3 "=r"))] + "!TARGET_CSSC" + "#" + "&& 1" + [(parallel + [(set (reg:CC_C CC_REGNUM) + (compare:CC_C (plus:GPI (match_dup ovf_commutate) + (match_dup <ovf_comm_opp>)) + (match_dup ovf_commutate))) + (set (match_dup 3) (plus:GPI (match_dup ovf_commutate) + (match_dup <ovf_comm_opp>)))]) + (set (match_dup 0) + (if_then_else:GPI (<ovf_add_cmp> (reg:CC_C CC_REGNUM) + (const_int 0)) + (match_dup 3) + (match_dup ovf_commutate)))] + { + if (GET_CODE (operands[3]) == SCRATCH) + operands[3] = gen_reg_rtx (<MODE>mode); + } +) + +;; umax (a, sub (a, b)) => [diff, udf] = subs (a, b); udf ? diff : a +;; umin (a, sub (a, b)) => [diff, udf] = subs (a, b); udf ? a : diff +(define_insn_and_split "*aarch64_minus_within_<optab><mode>3" + [(set (match_operand:GPI 0 "register_operand" "=r") + (UMAXMIN:GPI + (minus:GPI (match_operand:GPI 1 "register_operand" "r") + (match_operand:GPI 2 "register_operand" "r")) + (match_dup 1))) + (clobber (match_scratch:GPI 3 "=r"))] + "!TARGET_CSSC" + "#" + "&& 1" + [(parallel + [(set (reg:CC CC_REGNUM) + (compare:CC (match_dup 1) (match_dup 2))) + (set (match_dup 3) (minus:GPI (match_dup 1) (match_dup 2)))]) + (set (match_dup 0) + (if_then_else:GPI (<udf_sub_cmp> (reg:CC CC_REGNUM) + (const_int 0)) + (match_dup 3) + (match_dup 1)))] + { + if (GET_CODE (operands[3]) == SCRATCH) + operands[3] = gen_reg_rtx (<MODE>mode); + } +) + ;; ------------------------------------------------------------------- ;; Comparison insns ;; ------------------------------------------------------------------- diff --git a/gcc/config/aarch64/iterators.md b/gcc/config/aarch64/iterators.md index 82579b05ff7a..ff5688529d38 100644 --- a/gcc/config/aarch64/iterators.md +++ b/gcc/config/aarch64/iterators.md @@ -2853,6 +2853,8 @@ (define_code_iterator FMAXMIN [smax smin]) +(define_code_iterator UMAXMIN [umax umin]) + ;; Signed and unsigned max operations. (define_code_iterator USMAX [smax umax]) @@ -3141,6 +3143,9 @@ (define_code_attr maxminand [(smax "bic") (smin "and")]) +(define_code_attr ovf_add_cmp [(umax "geu") (umin "ltu")]) +(define_code_attr udf_sub_cmp [(umax "ltu") (umin "geu")]) + ;; MLA/MLS attributes. (define_code_attr as [(ss_plus "a") (ss_minus "s")]) @@ -5164,3 +5169,7 @@ (UNSPEC_F2CVT "f2cvt") (UNSPEC_F1CVTLT "f1cvtlt") (UNSPEC_F2CVTLT "f2cvtlt")]) + +;; Operand numbers for commutative operations +(define_int_iterator ovf_commutate [1 2]) +(define_int_attr ovf_comm_opp [(1 "2") (2 "1")]) diff --git a/gcc/testsuite/gcc.target/aarch64/pr116815-1.c b/gcc/testsuite/gcc.target/aarch64/pr116815-1.c new file mode 100644 index 000000000000..f3bdb7943188 --- /dev/null +++ b/gcc/testsuite/gcc.target/aarch64/pr116815-1.c @@ -0,0 +1,120 @@ +/* { dg-do compile } */ +/* { dg-options "-O2" } */ +/* { dg-final { check-function-bodies "**" "" "" } } */ + +/* PR middle-end/116815 */ + +/* Single-use tests. */ + +static inline unsigned __attribute__ ((always_inline)) +max (unsigned a, unsigned b) +{ + return a > b ? a : b; +} + +static inline unsigned __attribute__ ((always_inline)) +min (unsigned a, unsigned b) +{ + return a < b ? a : b; +} + +#define OPERATION(op, type, N, exp1, exp2) \ + unsigned u##op##type##N (unsigned a, unsigned b) { return op (exp1, exp2); } + +/* +** umaxadd1: +** adds (w[0-9]+), w0, w1 +** csel w0, \1, w0, cc +** ret +*/ +OPERATION (max, add, 1, a, a + b) + +/* +** umaxadd2: +** adds (w[0-9]+), w0, w1 +** csel w0, \1, w0, cc +** ret +*/ +OPERATION (max, add, 2, a, b + a) + +/* +** umaxadd3: +** adds (w[0-9]+), w0, w1 +** csel w0, \1, w0, cc +** ret +*/ +OPERATION (max, add, 3, a + b, a) + +/* +** umaxadd4: +** adds (w[0-9]+), w0, w1 +** csel w0, \1, w0, cc +** ret +*/ +OPERATION (max, add, 4, b + a, a) + +/* +** uminadd1: +** adds (w[0-9]+), w0, w1 +** csel w0, \1, w0, cs +** ret +*/ +OPERATION (min, add, 1, a, a + b) + +/* +** uminadd2: +** adds (w[0-9]+), w0, w1 +** csel w0, \1, w0, cs +** ret +*/ +OPERATION (min, add, 2, a, b + a) + +/* +** uminadd3: +** adds (w[0-9]+), w0, w1 +** csel w0, \1, w0, cs +** ret +*/ +OPERATION (min, add, 3, a + b, a) + +/* +** uminadd4: +** adds (w[0-9]+), w0, w1 +** csel w0, \1, w0, cs +** ret +*/ +OPERATION (min, add, 4, b + a, a) + +/* sub requires the inverse of the comparison from add. */ + +/* +** umaxsub1: +** subs (w[0-9]+), w0, w1 +** csel w0, \1, w0, cc +** ret +*/ +OPERATION (max, sub, 1, a, a - b) + +/* +** umaxsub2: +** subs (w[0-9]+), w0, w1 +** csel w0, \1, w0, cc +** ret +*/ +OPERATION (max, sub, 2, a - b, a) + +/* +** uminsub1: +** subs (w[0-9]+), w0, w1 +** csel w0, \1, w0, cs +** ret +*/ +OPERATION (min, sub, 1, a, a - b) + +/* +** uminsub2: +** subs (w[0-9]+), w0, w1 +** csel w0, \1, w0, cs +** ret +*/ +OPERATION (min, sub, 2, a - b, a) diff --git a/gcc/testsuite/gcc.target/aarch64/pr116815-2.c b/gcc/testsuite/gcc.target/aarch64/pr116815-2.c new file mode 100644 index 000000000000..015c868aec28 --- /dev/null +++ b/gcc/testsuite/gcc.target/aarch64/pr116815-2.c @@ -0,0 +1,44 @@ +/* { dg-do compile } */ +/* { dg-options "-O2" } */ + +#pragma GCC target "+cssc" + +/* PR middle-end/116815 */ + +/* Make sure that umax/umin instructions are generated with CSSC. */ + +static inline unsigned __attribute__ ((always_inline)) +max (unsigned a, unsigned b) +{ + return a > b ? a : b; +} + +static inline unsigned __attribute__ ((always_inline)) +min (unsigned a, unsigned b) +{ + return a < b ? a : b; +} + +#define OPERATION(op, type, N, exp1, exp2) \ + unsigned u##op##type##N (unsigned a, unsigned b) { return op (exp1, exp2); } + +OPERATION (max, add, 1, a, a + b) +OPERATION (max, add, 2, a, b + a) +OPERATION (max, add, 3, a + b, a) +OPERATION (max, add, 4, b + a, a) + +OPERATION (min, add, 1, a, a + b) +OPERATION (min, add, 2, a, b + a) +OPERATION (min, add, 3, a + b, a) +OPERATION (min, add, 4, b + a, a) + +OPERATION (max, sub, 1, a, a - b) +OPERATION (max, sub, 2, a - b, a) + +OPERATION (min, sub, 1, a, a - b) +OPERATION (min, sub, 2, a - b, a) + +/* { dg-final { scan-assembler-times "umax\\t" 6 } } */ +/* { dg-final { scan-assembler-times "umin\\t" 6 } } */ +/* { dg-final { scan-assembler-not "adds\\t" } } */ +/* { dg-final { scan-assembler-not "subs\\t" } } */ diff --git a/gcc/testsuite/gcc.target/aarch64/pr116815-3.c b/gcc/testsuite/gcc.target/aarch64/pr116815-3.c new file mode 100644 index 000000000000..d262d2170f39 --- /dev/null +++ b/gcc/testsuite/gcc.target/aarch64/pr116815-3.c @@ -0,0 +1,60 @@ +/* { dg-do run } */ +/* { dg-options "-O2" } */ + +/* PR middle-end/116815 */ + +/* Verify that the transformation gives correct results */ + +static inline unsigned __attribute__ ((always_inline)) +min (unsigned a, unsigned b) +{ + return (a < b) ? a : b; +} + +static inline unsigned __attribute__ ((always_inline)) +max (unsigned a, unsigned b) +{ + return (a > b) ? a : b; +} + +__attribute__ ((noipa)) unsigned +umaxadd (unsigned a, unsigned b) +{ + return max (a + b, a); +} + +__attribute__ ((noipa)) unsigned +umaxsub (unsigned a, unsigned b) +{ + return max (a - b, a); +} + +__attribute__ ((noipa)) unsigned +uminadd (unsigned a, unsigned b) +{ + return min (a + b, a); +} + +__attribute__ ((noipa)) unsigned +uminsub (unsigned a, unsigned b) +{ + return min (a - b, a); +} + +int +main () +{ + /* Overflows to 0x30000000. */ + if (umaxadd (0x90000000, 0xa0000000) != 0x90000000) + __builtin_abort (); + + if (uminadd (0x90000000, 0xa0000000) != 0x30000000) + __builtin_abort (); + + /* Underflows to 0x60000000. */ + if (umaxsub (0x00000000, 0xa0000000) != 0x60000000) + __builtin_abort (); + + if (uminsub (0x00000000, 0xa0000000) != 0x00000000) + __builtin_abort (); +}
