[llvm] 2e58010 - [DSE] Do not scan users of memory terminators for further reads.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2020-10-20T16:55:22+01:00
New Revision: 2e580102082293f9f80160bc86413e401c566d8f

URL: https://github.com/llvm/llvm-project/commit/2e580102082293f9f80160bc86413e401c566d8f
DIFF: https://github.com/llvm/llvm-project/commit/2e580102082293f9f80160bc86413e401c566d8f.diff

LOG: [DSE] Do not scan users of memory terminators for further reads.

isMemTerminator checks if the current def is a memory terminator that
terminates the memory pointed to by DefLoc. We do not have to add any of
their users to the worklist, because the follow-on users cannot read the
memory in question.

This leads to more stores eliminated in the presence of lifetime calls.
Previously we added the users of those intrinsics to the worklist,
limiting elimination.

In terms of removed stores, this gives a nice boost on some benchmarks
(MultiSource/SPEC2000/SPEC2006 on X86 with -flto -O3):

Same hash: 205 (filtered out)
Remaining: 32
Metric: dse.NumFastStores

Program                                          base   patch   diff
 test-suite...000/197.parser/197.parser.test     4.00    8.00  100.0%
 test-suite...rolangs-C++/family/family.test     4.00    7.00  75.0%
 test-suite...marks/7zip/7zip-benchmark.test   1722.00 2189.00 27.1%
 test-suite...CFP2000/177.mesa/177.mesa.test    30.00   38.00  26.7%
 test-suite :: External/Nurbs/nurbs.test        44.00   49.00  11.4%
 test-suite...lications/sqlite3/sqlite3.test   115.00  128.00  11.3%
 test-suite...006/447.dealII/447.dealII.test   2715.00 3013.00 11.0%
 test-suite...ProxyApps-C++/CLAMR/CLAMR.test   237.00  261.00  10.1%
 test-suite...tions/lambda-0.1.3/lambda.test    40.00   44.00  10.0%
 test-suite...3.xalancbmk/483.xalancbmk.test   1366.00 1475.00  8.0%
 test-suite...abench/jpeg/jpeg-6a/cjpeg.test    13.00   14.00   7.7%
 test-suite...oxyApps-C++/miniFE/miniFE.test    43.00   46.00   7.0%
 test-suite...lications/ClamAV/clamscan.test   230.00  246.00   7.0%
 test-suite...006/450.soplex/450.soplex.test   284.00  299.00   5.3%
 test-suite...nsumer-jpeg/consumer-jpeg.test    21.00   22.00   4.8%

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
    llvm/test/Transforms/DeadStoreElimination/MSSA/lifetime.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 58deceaba60f..75cd65b4dfea 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -2140,17 +2140,21 @@ struct DSEState {
         continue;
       }
 
+      // A memory terminator kills all preceeding MemoryDefs and all succeeding
+      // MemoryAccesses. We do not have to check it's users.
+      if (isMemTerminator(DefLoc, KillingI, UseInst)) {
+        LLVM_DEBUG(
+            dbgs()
+            << " ... skipping, memterminator invalidates following accesses\n");
+        continue;
+      }
+
       if (isNoopIntrinsic(cast<MemoryUseOrDef>(UseAccess)->getMemoryInst())) {
         LLVM_DEBUG(dbgs() << "    ... adding uses of intrinsic\n");
         PushMemUses(UseAccess);
         continue;
       }
 
-      // A memory terminator kills all preceeding MemoryDefs and all succeeding
-      // MemoryAccesses. We do not have to check it's users.
-      if (isMemTerminator(DefLoc, KillingI, UseInst))
-        continue;
-
       if (UseInst->mayThrow() && !isInvisibleToCallerBeforeRet(DefUO)) {
         LLVM_DEBUG(dbgs() << "  ... found throwing instruction\n");
         Cache.KnownReads.insert(UseAccess);

diff  --git a/llvm/test/Transforms/DeadStoreElimination/MSSA/lifetime.ll b/llvm/test/Transforms/DeadStoreElimination/MSSA/lifetime.ll
index 6184c89be5c4..c54f1593a93d 100644
--- a/llvm/test/Transforms/DeadStoreElimination/MSSA/lifetime.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/MSSA/lifetime.ll
@@ -84,8 +84,6 @@ define void @test4_lifetime_end_partial_loop() {
 ; CHECK-NEXT:    [[A_2:%.*]] = getelementptr i8, i8* [[A_0]], i64 2
 ; CHECK-NEXT:    call void @use(i8* [[A_1]])
 ; CHECK-NEXT:    store i8 20, i8* [[A_2]], align 1
-; CHECK-NEXT:    store i8 10, i8* [[A_1]], align 1
-; CHECK-NEXT:    store i8 0, i8* [[A_0]], align 1
 ; CHECK-NEXT:    call void @llvm.lifetime.end.p0i8(i64 2, i8* [[A_0]])
 ; CHECK-NEXT:    [[IV_NEXT]] = add i8 [[IV]], 10
 ; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i8 [[IV_NEXT]], 10