From 49fb0af9bf8f16907980d383c2bbc85e185ec2e0 Mon Sep 17 00:00:00 2001 From: Roger Sayle Date: Tue, 15 Mar 2022 09:05:28 +0000 Subject: PR tree-optimization/101895: Fold VEC_PERM to help recognize FMA. This patch resolves PR tree-optimization/101895 a missed optimization regression, by adding a costant folding simplification to match.pd to simplify the transform "mult; vec_perm; plus" into "vec_perm; mult; plus" with the aim that keeping the multiplication and addition next to each other allows them to be recognized as fused-multiply-add on suitable targets. This transformation requires a tweak to match.pd's vec_same_elem_p predicate to handle CONSTRUCTOR_EXPRs using the same SSA_NAME_DEF_STMT idiom used for constructors elsewhere in match.pd. The net effect is that the following code example: void foo(float * __restrict__ a, float b, float *c) { a[0] = c[0]*b + a[0]; a[1] = c[2]*b + a[1]; a[2] = c[1]*b + a[2]; a[3] = c[3]*b + a[3]; } when compiled on x86_64-pc-linux-gnu with -O2 -march=cascadelake currently generates: vbroadcastss %xmm0, %xmm0 vmulps (%rsi), %xmm0, %xmm0 vpermilps $216, %xmm0, %xmm0 vaddps (%rdi), %xmm0, %xmm0 vmovups %xmm0, (%rdi) ret but with this patch now generates the improved: vpermilps $216, (%rsi), %xmm1 vbroadcastss %xmm0, %xmm0 vfmadd213ps (%rdi), %xmm0, %xmm1 vmovups %xmm1, (%rdi) ret 2022-03-15 Roger Sayle Marc Glisse Richard Biener gcc/ChangeLog PR tree-optimization/101895 * match.pd (vec_same_elem_p): Handle CONSTRUCTOR_EXPR def. (plus (vec_perm (mult ...) ...) ...): New reordering simplification. gcc/testsuite/ChangeLog PR tree-optimization/101895 * gcc.target/i386/pr101895.c: New test case. --- gcc/match.pd | 21 +++++++++++++++++++-- gcc/testsuite/gcc.target/i386/pr101895.c | 11 +++++++++++ 2 files changed, 30 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/gcc.target/i386/pr101895.c (limited to 'gcc') diff --git a/gcc/match.pd b/gcc/match.pd index 8b44b5c..7d619f4 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -7692,16 +7692,33 @@ and, /* VEC_PERM_EXPR (v, v, mask) -> v where v contains same element. */ (match vec_same_elem_p + (vec_duplicate @0)) + +(match vec_same_elem_p + CONSTRUCTOR@0 + (if (TREE_CODE (@0) == SSA_NAME + && uniform_vector_p (gimple_assign_rhs1 (SSA_NAME_DEF_STMT (@0)))))) + +(match vec_same_elem_p @0 (if (uniform_vector_p (@0)))) -(match vec_same_elem_p - (vec_duplicate @0)) (simplify (vec_perm vec_same_elem_p@0 @0 @1) @0) +/* Push VEC_PERM earlier if that may help FMA perception (PR101895). */ +(simplify + (plus:c (vec_perm:s (mult:c@0 @1 vec_same_elem_p@2) @0 @3) @4) + (if (TREE_CODE (@0) == SSA_NAME && num_imm_uses (@0) == 2) + (plus (mult (vec_perm @1 @1 @3) @2) @4))) +(simplify + (minus (vec_perm:s (mult:c@0 @1 vec_same_elem_p@2) @0 @3) @4) + (if (TREE_CODE (@0) == SSA_NAME && num_imm_uses (@0) == 2) + (minus (mult (vec_perm @1 @1 @3) @2) @4))) + + /* Match count trailing zeroes for simplify_count_trailing_zeroes in fwprop. The canonical form is array[((x & -x) * C) >> SHIFT] where C is a magic constant which when multiplied by a power of 2 contains a unique value diff --git a/gcc/testsuite/gcc.target/i386/pr101895.c b/gcc/testsuite/gcc.target/i386/pr101895.c new file mode 100644 index 0000000..4d0f1cb --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr101895.c @@ -0,0 +1,11 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -march=cascadelake" } */ + +void foo(float * __restrict__ a, float b, float *c) { + a[0] = c[0]*b + a[0]; + a[1] = c[2]*b + a[1]; + a[2] = c[1]*b + a[2]; + a[3] = c[3]*b + a[3]; +} + +/* { dg-final { scan-assembler "vfmadd" } } */ -- cgit v1.1