From 1a6c1c85b7ab1ad4bdf9573fcdc04dcce894ba82 Mon Sep 17 00:00:00 2001 From: Martin Jambor Date: Thu, 9 May 2024 16:39:44 +0200 Subject: [PATCH] sra: Do not leave work for DSE (that it can sometimes not perform) When looking again at the g++.dg/tree-ssa/pr109849.C testcase we discovered that it generates terrible store-to-load forwarding stalls because SRA was leaving behind aggregate loads but all the stores were by scalar parts and DSE failed to remove the useless load. SRA has all the knowledge to remove the statement even now, so this small patch makes it do so. With this patch, the g++.dg/tree-ssa/pr109849.C micro-benchmark runs 9 times faster (on an AMD EPYC 75F3 machine). gcc/ChangeLog: 2024-04-18 Martin Jambor * tree-sra.cc (sra_modify_assign): Remove the original statement also when dealing with a store to a fully covered aggregate from a non-candidate. gcc/testsuite/ChangeLog: 2024-04-23 Martin Jambor * g++.dg/tree-ssa/pr109849.C: Also check that the aggeegate store to cur disappears. * gcc.dg/tree-ssa/ssa-dse-26.c: Instead of relying on DSE, check that the unwanted stores were removed at early SRA time. (cherry picked from commit f6743695b4d2bd4da96e56a19157372f93b800bd) --- gcc/testsuite/g++.dg/tree-ssa/pr109849.C | 3 ++- gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-26.c | 6 +++--- gcc/tree-sra.cc | 14 ++++++++++++-- 3 files changed, 17 insertions(+), 6 deletions(-) diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr109849.C b/gcc/testsuite/g++.dg/tree-ssa/pr109849.C index cd348c0f590..d06dbb10482 100644 --- a/gcc/testsuite/g++.dg/tree-ssa/pr109849.C +++ b/gcc/testsuite/g++.dg/tree-ssa/pr109849.C @@ -1,5 +1,5 @@ /* { dg-do compile } */ -/* { dg-options "-O2 -fdump-tree-sra" } */ +/* { dg-options "-O2 -fdump-tree-sra -fdump-tree-optimized" } */ #include typedef unsigned int uint32_t; @@ -29,3 +29,4 @@ main() } /* { dg-final { scan-tree-dump "Created a replacement for stack offset" "sra"} } */ +/* { dg-final { scan-tree-dump-not "cur = MEM" "optimized"} } */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-26.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-26.c index 43152de5616..1d01392c595 100644 --- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-26.c +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-26.c @@ -1,5 +1,5 @@ /* { dg-do compile } */ -/* { dg-options "-O2 -fdump-tree-dse1-details -fno-short-enums -fno-tree-fre" } */ +/* { dg-options "-O2 -fdump-tree-esra -fno-short-enums -fno-tree-fre" } */ /* { dg-skip-if "we want a BIT_FIELD_REF from fold_truth_andor" { ! lp64 } } */ /* { dg-skip-if "temporary variable names are not x and y" { mmix-knuth-mmixware } } */ @@ -31,5 +31,5 @@ constraint_equal (struct constraint a, struct constraint b) && constraint_expr_equal (a.rhs, b.rhs); } -/* { dg-final { scan-tree-dump-times "Deleted dead store: x = " 2 "dse1" } } */ -/* { dg-final { scan-tree-dump-times "Deleted dead store: y = " 2 "dse1" } } */ +/* { dg-final { scan-tree-dump-not "x = " "esra" } } */ +/* { dg-final { scan-tree-dump-not "y = " "esra" } } */ diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc index 32fa28911f2..8040b0c5645 100644 --- a/gcc/tree-sra.cc +++ b/gcc/tree-sra.cc @@ -4854,8 +4854,18 @@ sra_modify_assign (gimple *stmt, gimple_stmt_iterator *gsi) But use the RHS aggregate to load from to expose more optimization opportunities. */ if (access_has_children_p (lacc)) - generate_subtree_copies (lacc->first_child, rhs, lacc->offset, - 0, 0, gsi, true, true, loc); + { + generate_subtree_copies (lacc->first_child, rhs, lacc->offset, + 0, 0, gsi, true, true, loc); + if (lacc->grp_covered) + { + unlink_stmt_vdef (stmt); + gsi_remove (& orig_gsi, true); + release_defs (stmt); + sra_stats.deleted++; + return SRA_AM_REMOVED; + } + } } return SRA_AM_NONE;