From 976401aa4781fa5850e1f34142bc13d1cfe0b2bd Mon Sep 17 00:00:00 2001 From: Roger Sayle Date: Fri, 20 Aug 2021 00:24:23 +0100 Subject: [PATCH] Fold more constants during veclower pass. An issue with a backend patch I've been investigating has revealed a missed optimization opportunity during GCC's vector lowering pass. An unrecognized insn for "(set (reg:SI) (not:SI (const_int 0))" revealed that not only was my expander not expecting a NOT with a constant operand, but also that veclower was producing the dubious tree expression ~0. The attached patch replaces a call to gimple_build_assign with a call to either gimplify_build1 or gimplify_build2 depending upon whether the operation takes one or two operands. The net effect is that where GCC previously produced the following optimized gimple for testsuite/c-c++common/Wunused-var-16.c (notice the ~0 and the "& 0"): void foo () { V x; V y; vector(16) unsigned char _1; unsigned char _7; unsigned char _8; y_2 = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; x_3 = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; _7 = ~0; _1 = {_7, _7, _7, _7, _7, _7, _7, _7, _7, _7, _7, _7, _7, _7, _7, _7}; _8 = 0 & _7; y_4 = {_8, _8, _8, _8, _8, _8, _8, _8, _8, _8, _8, _8, _8, _8, _8, _8}; v = y_4; return; } With this patch we now generate: void foo () { V x; V y; vector(16) unsigned char _1; y_2 = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; x_3 = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; _1 = { 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 2 55, 255 }; y_4 = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; v = y_4; return; } 2021-08-20 Roger Sayle gcc/ChangeLog * tree-vect-generic.c (expand_vector_operations_1): Use either gimplify_build1 or gimplify_build2 instead of gimple_build_assign when constructing scalar splat expressions. gcc/testsuite/ChangeLog * c-c++-common/Wunused-var-16.c: Add an extra check that ~0 is optimized away. --- gcc/testsuite/c-c++-common/Wunused-var-16.c | 4 +++- gcc/tree-vect-generic.c | 7 ++++--- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/gcc/testsuite/c-c++-common/Wunused-var-16.c b/gcc/testsuite/c-c++-common/Wunused-var-16.c index 8bdbcd33c1a4..31c7db30f9fa 100644 --- a/gcc/testsuite/c-c++-common/Wunused-var-16.c +++ b/gcc/testsuite/c-c++-common/Wunused-var-16.c @@ -1,6 +1,6 @@ /* PR c++/78949 */ /* { dg-do compile } */ -/* { dg-options "-Wunused" } */ +/* { dg-options "-Wunused -fdump-tree-optimized" } */ /* { dg-additional-options "-fno-common" { target hppa*-*-hpux* } } */ typedef unsigned char V __attribute__((vector_size(16))); @@ -14,3 +14,5 @@ foo () y &= ~x; v = y; } + +/* { dg-final { scan-tree-dump-not " ~0" "optimized" } } */ diff --git a/gcc/tree-vect-generic.c b/gcc/tree-vect-generic.c index 2e00b3ed3ca2..0d7f04126f22 100644 --- a/gcc/tree-vect-generic.c +++ b/gcc/tree-vect-generic.c @@ -2162,9 +2162,10 @@ expand_vector_operations_1 (gimple_stmt_iterator *gsi, if (op >= FIRST_NORM_OPTAB && op <= LAST_NORM_OPTAB && optab_handler (op, TYPE_MODE (TREE_TYPE (type))) != CODE_FOR_nothing) { - tree slhs = make_ssa_name (TREE_TYPE (TREE_TYPE (lhs))); - gimple *repl = gimple_build_assign (slhs, code, srhs1, srhs2); - gsi_insert_before (gsi, repl, GSI_SAME_STMT); + tree stype = TREE_TYPE (TREE_TYPE (lhs)); + tree slhs = (rhs2 != NULL_TREE) + ? gimplify_build2 (gsi, code, stype, srhs1, srhs2) + : gimplify_build1 (gsi, code, stype, srhs1); gimple_assign_set_rhs_from_tree (gsi, build_vector_from_val (type, slhs)); update_stmt (stmt); -- 2.47.2