From 3d48c11ad082def8ee237e5778d8a5d569bff96d Mon Sep 17 00:00:00 2001 From: Richard Biener Date: Thu, 3 Aug 2023 10:59:52 +0200 Subject: [PATCH] Swap loop splitting and final value replacement The following swaps the loop splitting pass and the final value replacement pass to avoid keeping the IV of the earlier loop live when not necessary. The existing gcc.target/i386/pr87007-5.c testcase shows that we otherwise fail to elide an empty loop later. I don't see any good reason why loop splitting would need final value replacement, all exit values honor the constraints we place on loop header PHIs automatically. * passes.def: Exchange loop splitting and final value replacement passes. * gcc.target/i386/pr87007-5.c: Make sure we split the loop and eliminate both in the end. --- gcc/passes.def | 2 +- gcc/testsuite/gcc.target/i386/pr87007-5.c | 4 +++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/gcc/passes.def b/gcc/passes.def index f2893ae8a8b..ef5a21afe49 100644 --- a/gcc/passes.def +++ b/gcc/passes.def @@ -282,8 +282,8 @@ along with GCC; see the file COPYING3. If not see form if possible. */ NEXT_PASS (pass_tree_loop_init); NEXT_PASS (pass_tree_unswitch); - NEXT_PASS (pass_scev_cprop); NEXT_PASS (pass_loop_split); + NEXT_PASS (pass_scev_cprop); NEXT_PASS (pass_loop_versioning); NEXT_PASS (pass_loop_jam); /* All unswitching, final value replacement and splitting can expose diff --git a/gcc/testsuite/gcc.target/i386/pr87007-5.c b/gcc/testsuite/gcc.target/i386/pr87007-5.c index b36e81c270c..a6cdf11522e 100644 --- a/gcc/testsuite/gcc.target/i386/pr87007-5.c +++ b/gcc/testsuite/gcc.target/i386/pr87007-5.c @@ -1,5 +1,5 @@ /* { dg-do compile } */ -/* { dg-options "-Ofast -march=skylake-avx512 -mfpmath=sse -fno-tree-vectorize" } */ +/* { dg-options "-Ofast -march=skylake-avx512 -mfpmath=sse -fno-tree-vectorize -fdump-tree-cddce3-details -fdump-tree-lsplit-optimized" } */ /* Load of d2/d3 is hoisted out, vrndscalesd will reuse loades register to avoid partial dependence. */ #include @@ -15,4 +15,6 @@ foo (int n, int k) d1 = sqrt (d3); } +/* { dg-final { scan-tree-dump "optimized: loop split" "lsplit" } } */ +/* { dg-final { scan-tree-dump-times "removing loop" 2 "cddce3" } } */ /* { dg-final { scan-assembler-times "vxorps\[^\n\r\]*xmm\[0-9\]" 0 } } */