From 97671565ffd341d1d3291243f9f51edc6b64b065 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Mon, 15 Aug 2011 20:52:09 +0000
Subject: [PATCH] Atomic load/store support in LICM.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137648 91177308-0d34-0410-b5e6-96231b3b80d8
---
lib/Analysis/AliasSetTracker.cpp | 12 +++--
lib/Transforms/Scalar/LICM.cpp | 16 ++++---
test/Transforms/LICM/atomics.ll | 79 ++++++++++++++++++++++++++++++++
3 files changed, 97 insertions(+), 10 deletions(-)
create mode 100644 test/Transforms/LICM/atomics.ll
diff --git a/lib/Analysis/AliasSetTracker.cpp b/lib/Analysis/AliasSetTracker.cpp
index a11142d0e15..3fcd3b55de5 100644
--- a/lib/Analysis/AliasSetTracker.cpp
+++ b/lib/Analysis/AliasSetTracker.cpp
@@ -126,8 +126,6 @@ void AliasSet::addPointer(AliasSetTracker &AST, PointerRec &Entry,
void AliasSet::addUnknownInst(Instruction *I, AliasAnalysis &AA) {
UnknownInsts.push_back(I);
- if (!I->mayReadOrWriteMemory())
- return;
if (!I->mayWriteToMemory()) {
AliasTy = MayAlias;
AccessTy |= Refs;
@@ -297,22 +295,28 @@ bool AliasSetTracker::add(Value *Ptr, uint64_t Size, const MDNode *TBAAInfo) {
bool AliasSetTracker::add(LoadInst *LI) {
+ if (LI->getOrdering() > Monotonic) return addUnknown(LI);
+ AliasSet::AccessType ATy = AliasSet::Refs;
+ if (!LI->isUnordered()) ATy = AliasSet::ModRef;
bool NewPtr;
AliasSet &AS = addPointer(LI->getOperand(0),
AA.getTypeStoreSize(LI->getType()),
LI->getMetadata(LLVMContext::MD_tbaa),
- AliasSet::Refs, NewPtr);
+ ATy, NewPtr);
if (LI->isVolatile()) AS.setVolatile();
return NewPtr;
}
bool AliasSetTracker::add(StoreInst *SI) {
+ if (SI->getOrdering() > Monotonic) return addUnknown(SI);
+ AliasSet::AccessType ATy = AliasSet::Mods;
+ if (!SI->isUnordered()) ATy = AliasSet::ModRef;
bool NewPtr;
Value *Val = SI->getOperand(0);
AliasSet &AS = addPointer(SI->getOperand(1),
AA.getTypeStoreSize(Val->getType()),
SI->getMetadata(LLVMContext::MD_tbaa),
- AliasSet::Mods, NewPtr);
+ ATy, NewPtr);
if (SI->isVolatile()) AS.setVolatile();
return NewPtr;
}
diff --git a/lib/Transforms/Scalar/LICM.cpp b/lib/Transforms/Scalar/LICM.cpp
index c9cfb87737e..79bdf906752 100644
--- a/lib/Transforms/Scalar/LICM.cpp
+++ b/lib/Transforms/Scalar/LICM.cpp
@@ -362,8 +362,8 @@ void LICM::HoistRegion(DomTreeNode *N) {
bool LICM::canSinkOrHoistInst(Instruction &I) {
// Loads have extra constraints we have to verify before we can hoist them.
if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
- if (LI->isVolatile())
- return false; // Don't hoist volatile loads!
+ if (!LI->isUnordered())
+ return false; // Don't hoist volatile/atomic loads!
// Loads from constant memory are always safe to move, even if they end up
// in the same alias set as something that ends up being modified.
@@ -722,15 +722,18 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
// If there is an non-load/store instruction in the loop, we can't promote
// it.
- if (isa<LoadInst>(Use)) {
- assert(!cast<LoadInst>(Use)->isVolatile() && "AST broken");
+ if (LoadInst *load = dyn_cast<LoadInst>(Use)) {
+ assert(!load->isVolatile() && "AST broken");
+ if (!load->isSimple())
+ return;
} else if (StoreInst *store = dyn_cast<StoreInst>(Use)) {
// Stores *of* the pointer are not interesting, only stores *to* the
// pointer.
if (Use->getOperand(1) != ASIV)
continue;
- unsigned InstAlignment = store->getAlignment();
- assert(!cast<StoreInst>(Use)->isVolatile() && "AST broken");
+ assert(!store->isVolatile() && "AST broken");
+ if (!store->isSimple())
+ return;
// Note that we only check GuaranteedToExecute inside the store case
// so that we do not introduce stores where they did not exist before
@@ -740,6 +743,7 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
// restrictive (and performant) alignment and if we are sure this
// instruction will be executed, update the alignment.
// Larger is better, with the exception of 0 being the best alignment.
+ unsigned InstAlignment = store->getAlignment();
if ((InstAlignment > Alignment || InstAlignment == 0)
&& (Alignment != 0))
if (isGuaranteedToExecute(*Use)) {
diff --git a/test/Transforms/LICM/atomics.ll b/test/Transforms/LICM/atomics.ll
new file mode 100644
index 00000000000..3902152ba2e
--- /dev/null
+++ b/test/Transforms/LICM/atomics.ll
@@ -0,0 +1,79 @@
+; RUN: opt < %s -S -basicaa -licm | FileCheck %s
+
+; Check that we can hoist unordered loads
+define i32 @test1(i32* nocapture %y) nounwind uwtable ssp {
+entry:
+ br label %loop
+
+loop:
+ %i = phi i32 [ %inc, %loop ], [ 0, %entry ]
+ %val = load atomic i32* %y unordered, align 4
+ %inc = add nsw i32 %i, 1
+ %exitcond = icmp eq i32 %inc, %val
+ br i1 %exitcond, label %end, label %loop
+
+end:
+ ret i32 %val
+; CHECK: define i32 @test1(
+; CHECK: load atomic
+; CHECK-NEXT: br label %loop
+}
+
+; Check that we don't sink/hoist monotonic loads
+; (Strictly speaking, it's not forbidden, but it's supposed to be possible to
+; use monotonic for spinlock-like constructs.)
+define i32 @test2(i32* nocapture %y) nounwind uwtable ssp {
+entry:
+ br label %loop
+
+loop:
+ %val = load atomic i32* %y monotonic, align 4
+ %exitcond = icmp ne i32 %val, 0
+ br i1 %exitcond, label %end, label %loop
+
+end:
+ ret i32 %val
+; CHECK: define i32 @test2(
+; CHECK: load atomic
+; CHECK-NEXT: %exitcond = icmp ne
+; CHECK-NEXT: br i1 %exitcond, label %end, label %loop
+}
+
+; Check that we hoist unordered around monotonic.
+; (The noalias shouldn't be necessary in theory, but LICM isn't quite that
+; smart yet.)
+define i32 @test3(i32* nocapture noalias %x, i32* nocapture %y) nounwind uwtable ssp {
+entry:
+ br label %loop
+
+loop:
+ %vala = load atomic i32* %y monotonic, align 4
+ %valb = load atomic i32* %x unordered, align 4
+ %exitcond = icmp ne i32 %vala, %valb
+ br i1 %exitcond, label %end, label %loop
+
+end:
+ ret i32 %vala
+; CHECK: define i32 @test3(
+; CHECK: load atomic i32* %x unordered
+; CHECK-NEXT: br label %loop
+}
+
+; Don't try to "sink" unordered stores yet; it is legal, but the machinery
+; isn't there.
+define i32 @test4(i32* nocapture noalias %x, i32* nocapture %y) nounwind uwtable ssp {
+entry:
+ br label %loop
+
+loop:
+ %vala = load atomic i32* %y monotonic, align 4
+ store atomic i32 %vala, i32* %x unordered, align 4
+ %exitcond = icmp ne i32 %vala, 0
+ br i1 %exitcond, label %end, label %loop
+
+end:
+ ret i32 %vala
+; CHECK: define i32 @test4(
+; CHECK: load atomic i32* %y monotonic
+; CHECK-NEXT: store atomic
+}