[llvm] b82f800 - [DSE] Use walker to skip noalias stores between current & clobber def.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2020-10-28T11:01:25Z
New Revision: b82f80057d69564a889f1439a683c3544d30b7fa

URL: https://github.com/llvm/llvm-project/commit/b82f80057d69564a889f1439a683c3544d30b7fa
DIFF: https://github.com/llvm/llvm-project/commit/b82f80057d69564a889f1439a683c3544d30b7fa.diff

LOG: [DSE] Use walker to skip noalias stores between current & clobber def.

Instead of getting the defining access we should be able to use
getClobberingMemoryAccess to skip non-aliasing MemoryDefs. No additional
checks should be needed, because we only remove the starting def if it
matches the defining access of the load. All we need to worry about is
that there are no (may)alias stores between the starting def and the
load and getClobberingMemoryAccess should guarantee that.

Partly fixes PR47887.

This improves the number of redundant stores removed in some cases
(numbers below for MultiSource, SPEC2000, SPEC2006 on X86 with -flto
-O3).

Same hash: 226 (filtered out)
Remaining: 11
Metric: dse.NumRedundantStores

Program                                        base   patch1 diff
 test-suite...:: External/Povray/povray.test     1.00   5.00 400.0%
 test-suite...chmarks/MallocBench/gs/gs.test     1.00   3.00 200.0%
 test-suite...0/253.perlbmk/253.perlbmk.test    21.00  37.00 76.2%
 test-suite...0.perlbench/400.perlbench.test    24.00  37.00 54.2%
 test-suite.../Applications/SPASS/SPASS.test     3.00   4.00 33.3%
 test-suite...006/453.povray/453.povray.test    15.00  18.00 20.0%
 test-suite...T2006/445.gobmk/445.gobmk.test    27.00  29.00  7.4%
 test-suite.../CINT2006/403.gcc/403.gcc.test   136.00 137.00  0.7%
 test-suite.../CINT2000/176.gcc/176.gcc.test     6.00   6.00  0.0%
 test-suite.../Benchmarks/Bullet/bullet.test    NaN     3.00  nan%
 test-suite.../Benchmarks/Ptrdist/bc/bc.test    NaN     1.00  nan%

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D89647

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
    llvm/test/Transforms/DeadStoreElimination/MSSA/noop-stores.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 75cd65b4dfea..273805031424 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -2426,7 +2426,8 @@ struct DSEState {
         // adding them to a worklist. Bail when we run into a memory def that
         // does not match LoadAccess.
         SetVector<MemoryAccess *> ToCheck;
-        MemoryAccess *Current = Def->getDefiningAccess();
+        MemoryAccess *Current =
+            MSSA.getWalker()->getClobberingMemoryAccess(Def);
         // We don't want to bail when we run into the store memory def. But,
         // the phi access may point to it. So, pretend like we've already
         // checked it.

diff  --git a/llvm/test/Transforms/DeadStoreElimination/MSSA/noop-stores.ll b/llvm/test/Transforms/DeadStoreElimination/MSSA/noop-stores.ll
index 22bf3951e4db..97fa988bae18 100644
--- a/llvm/test/Transforms/DeadStoreElimination/MSSA/noop-stores.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/MSSA/noop-stores.ll
@@ -15,7 +15,6 @@ declare void @llvm.init.trampoline(i8*, i8*, i8*)
 define void @test_load_volatile(i32* %Q) {
 ; CHECK-LABEL: @test_load_volatile(
 ; CHECK-NEXT:    [[A:%.*]] = load volatile i32, i32* [[Q:%.*]], align 4
-; CHECK-NEXT:    store i32 [[A]], i32* [[Q]], align 4
 ; CHECK-NEXT:    ret void
 ;
   %a = load volatile i32, i32* %Q
@@ -284,9 +283,7 @@ bb3:
 define void @test_noalias_store_between_load_and_store(i32* noalias %x, i32* noalias %y) {
 ; CHECK-LABEL: @test_noalias_store_between_load_and_store(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[LV:%.*]] = load i32, i32* [[X:%.*]], align 4
 ; CHECK-NEXT:    store i32 0, i32* [[Y:%.*]], align 4
-; CHECK-NEXT:    store i32 [[LV]], i32* [[X]], align 4
 ; CHECK-NEXT:    ret void
 ;
 entry: