[llvm] r277640 - [MSSA] Add special handling for invariant/constant loads.
George Burgess IV via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 3 12:57:02 PDT 2016
Author: gbiv
Date: Wed Aug 3 14:57:02 2016
New Revision: 277640
URL: http://llvm.org/viewvc/llvm-project?rev=277640&view=rev
Log:
[MSSA] Add special handling for invariant/constant loads.
This is a follow-up to r277637. It teaches MemorySSA that invariant
loads (and loads of provably constant memory) are always liveOnEntry.
Modified:
llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp
llvm/trunk/test/Transforms/Util/MemorySSA/load-invariant.ll
llvm/trunk/unittests/Transforms/Utils/MemorySSA.cpp
Modified: llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp?rev=277640&r1=277639&r2=277640&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp Wed Aug 3 14:57:02 2016
@@ -170,6 +170,7 @@ template <> struct DenseMapInfo<MemoryLo
}
};
}
+
namespace {
struct UpwardsMemoryQuery {
// True if our original query started off as a call
@@ -251,6 +252,17 @@ static Reorderability getLoadReorderabil
return Result;
}
+static bool isUseTriviallyOptimizableToLiveOnEntry(AliasAnalysis &AA,
+ const Instruction *I) {
+ // If the memory can't be changed, then loads of the memory can't be
+ // clobbered.
+ //
+ // FIXME: We should handle invariant groups, as well. It's a bit harder,
+ // because we need to pay close attention to invariant group barriers.
+ return isa<LoadInst>(I) && (I->getMetadata(LLVMContext::MD_invariant_load) ||
+ AA.pointsToConstantMemory(I));
+}
+
static bool instructionClobbersQuery(MemoryDef *MD,
const MemoryLocation &UseLoc,
const Instruction *UseInst,
@@ -1332,6 +1344,11 @@ void MemorySSA::OptimizeUses::optimizeUs
continue;
}
+ if (isUseTriviallyOptimizableToLiveOnEntry(*AA, MU->getMemoryInst())) {
+ MU->setDefiningAccess(MSSA->getLiveOnEntryDef());
+ continue;
+ }
+
MemoryLocOrCall UseMLOC(MU);
auto &LocInfo = LocStackInfo[UseMLOC];
// If the pop epoch changed, it means we've removed stuff from top of
@@ -2246,6 +2263,12 @@ MemorySSA::CachingWalker::getClobberingM
if (auto *CacheResult = Cache.lookup(StartingAccess, Q.StartingLoc, Q.IsCall))
return CacheResult;
+ if (isUseTriviallyOptimizableToLiveOnEntry(*MSSA->AA, I)) {
+ MemoryAccess *LiveOnEntry = MSSA->getLiveOnEntryDef();
+ Cache.insert(StartingAccess, LiveOnEntry, Q.StartingLoc, Q.IsCall);
+ return LiveOnEntry;
+ }
+
// Start with the thing we already think clobbers this location
MemoryAccess *DefiningAccess = StartingAccess->getDefiningAccess();
Modified: llvm/trunk/test/Transforms/Util/MemorySSA/load-invariant.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Util/MemorySSA/load-invariant.ll?rev=277640&r1=277639&r2=277640&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/Util/MemorySSA/load-invariant.ll (original)
+++ llvm/trunk/test/Transforms/Util/MemorySSA/load-invariant.ll Wed Aug 3 14:57:02 2016
@@ -1,4 +1,3 @@
-; XFAIL: *
; RUN: opt -basicaa -print-memoryssa -verify-memoryssa -analyze < %s 2>&1 | FileCheck %s
; RUN: opt -aa-pipeline=basic-aa -passes='print<memoryssa>' -verify-memoryssa -disable-output < %s 2>&1 | FileCheck %s
;
@@ -12,6 +11,7 @@
declare void @clobberAllTheThings()
+; CHECK-LABEL: define i32 @foo
define i32 @foo() {
; CHECK: 1 = MemoryDef(liveOnEntry)
; CHECK-NEXT: call void @clobberAllTheThings()
@@ -22,4 +22,20 @@ define i32 @foo() {
ret i32 %1
}
+; CHECK-LABEL: define i32 @bar
+define i32 @bar(i32* %a) {
+; CHECK: 1 = MemoryDef(liveOnEntry)
+; CHECK-NEXT: call void @clobberAllTheThings()
+ call void @clobberAllTheThings()
+
+; CHECK: 2 = MemoryDef(1)
+; CHECK-NEXT: %1 = load atomic i32
+ %1 = load atomic i32, i32* %a acquire, align 4, !invariant.load !0
+
+; CHECK: MemoryUse(2)
+; CHECK-NEXT: %2 = load i32
+ %2 = load i32, i32* %a, align 4
+ ret i32 %2
+}
+
!0 = !{}
Modified: llvm/trunk/unittests/Transforms/Utils/MemorySSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Transforms/Utils/MemorySSA.cpp?rev=277640&r1=277639&r2=277640&view=diff
==============================================================================
--- llvm/trunk/unittests/Transforms/Utils/MemorySSA.cpp (original)
+++ llvm/trunk/unittests/Transforms/Utils/MemorySSA.cpp Wed Aug 3 14:57:02 2016
@@ -418,3 +418,36 @@ TEST_F(MemorySSATest, PartialWalkerCache
MemoryAccess *UseClobber = Walker->getClobberingMemoryAccess(ALoad);
EXPECT_EQ(UseClobber, MSSA.getMemoryAccess(FirstStore));
}
+
+// Test that our walker properly handles loads with the invariant group
+// attribute. It's a bit hacky, since we add the invariant attribute *after*
+// building MSSA. Otherwise, the use optimizer will optimize it for us, which
+// isn't what we want.
+// FIXME: It may be easier/cleaner to just add an 'optimize uses?' flag to MSSA.
+TEST_F(MemorySSATest, WalkerInvariantLoadOpt) {
+ F = Function::Create(FunctionType::get(B.getVoidTy(), {}, false),
+ GlobalValue::ExternalLinkage, "F", &M);
+ B.SetInsertPoint(BasicBlock::Create(C, "", F));
+ Type *Int8 = Type::getInt8Ty(C);
+ Constant *One = ConstantInt::get(Int8, 1);
+ Value *AllocA = B.CreateAlloca(Int8, One, "");
+
+ Instruction *Store = B.CreateStore(One, AllocA);
+ Instruction *Load = B.CreateLoad(AllocA);
+
+ setupAnalyses();
+ MemorySSA &MSSA = Analyses->MSSA;
+ MemorySSAWalker *Walker = Analyses->Walker;
+
+ auto *LoadMA = cast<MemoryUse>(MSSA.getMemoryAccess(Load));
+ auto *StoreMA = cast<MemoryDef>(MSSA.getMemoryAccess(Store));
+ EXPECT_EQ(LoadMA->getDefiningAccess(), StoreMA);
+
+ // ...At the time of writing, no cache should exist for LoadMA. Be a bit
+ // flexible to future changes.
+ Walker->invalidateInfo(LoadMA);
+ Load->setMetadata(LLVMContext::MD_invariant_load, MDNode::get(C, {}));
+
+ MemoryAccess *LoadClobber = Walker->getClobberingMemoryAccess(LoadMA);
+ EXPECT_EQ(LoadClobber, MSSA.getLiveOnEntryDef());
+}
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