[llvm] [SSAUpdaterBulk] Fix incorrect live-in values for a block. (PR #131762)
Valery Pykhtin via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 18 02:59:42 PDT 2025
https://github.com/vpykhtin updated https://github.com/llvm/llvm-project/pull/131762
>From 51fff2801c287b6b7f585493643c2a2d31b7b828 Mon Sep 17 00:00:00 2001
From: Valery Pykhtin <valery.pykhtin at amd.com>
Date: Mon, 17 Mar 2025 18:42:27 +0000
Subject: [PATCH 1/2] [SSAUpdaterBulk] Simplify SSAUpdaterBulk::RewriteAllUses.
NFC. - removed redundant resetLiveInBlocks - avoid temporary PHI holder
container.
---
llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp b/llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp
index cad7ff64c01fb..4bb2fb909c113 100644
--- a/llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp
+++ b/llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp
@@ -143,26 +143,23 @@ void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT,
SmallVector<BasicBlock *, 32> IDFBlocks;
SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
ComputeLiveInBlocks(UsingBlocks, DefBlocks, LiveInBlocks, PredCache);
- IDF.resetLiveInBlocks();
IDF.setLiveInBlocks(LiveInBlocks);
IDF.calculate(IDFBlocks);
// We've computed IDF, now insert new phi-nodes there.
- SmallVector<PHINode *, 4> InsertedPHIsForVar;
for (auto *FrontierBB : IDFBlocks) {
IRBuilder<> B(FrontierBB, FrontierBB->begin());
PHINode *PN = B.CreatePHI(R.Ty, 0, R.Name);
R.Defines[FrontierBB] = PN;
- InsertedPHIsForVar.push_back(PN);
if (InsertedPHIs)
InsertedPHIs->push_back(PN);
}
// Fill in arguments of the inserted PHIs.
- for (auto *PN : InsertedPHIsForVar) {
- BasicBlock *PBB = PN->getParent();
- for (BasicBlock *Pred : PredCache.get(PBB))
- PN->addIncoming(computeValueAt(Pred, R, DT), Pred);
+ for (auto *BB : IDFBlocks) {
+ auto *PHI = cast<PHINode>(&BB->front());
+ for (BasicBlock *Pred : PredCache.get(BB))
+ PHI->addIncoming(computeValueAt(Pred, R, DT), Pred);
}
// Rewrite actual uses with the inserted definitions.
>From 5761cf5bc31c95e516a532dee138c2dfbc7a97e4 Mon Sep 17 00:00:00 2001
From: Valery Pykhtin <valery.pykhtin at amd.com>
Date: Mon, 17 Mar 2025 19:01:43 +0000
Subject: [PATCH 2/2] [SSAUpdaterBulk] Fix incorrect live-in values for a
block.
---
.../llvm/Transforms/Utils/SSAUpdaterBulk.h | 4 +-
llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp | 70 +++++++++++++------
.../Transforms/Utils/SSAUpdaterBulkTest.cpp | 10 ++-
3 files changed, 54 insertions(+), 30 deletions(-)
diff --git a/llvm/include/llvm/Transforms/Utils/SSAUpdaterBulk.h b/llvm/include/llvm/Transforms/Utils/SSAUpdaterBulk.h
index ad24cb454d5e7..b2cf29608f58b 100644
--- a/llvm/include/llvm/Transforms/Utils/SSAUpdaterBulk.h
+++ b/llvm/include/llvm/Transforms/Utils/SSAUpdaterBulk.h
@@ -38,7 +38,7 @@ class DominatorTree;
/// is used).
class SSAUpdaterBulk {
struct RewriteInfo {
- DenseMap<BasicBlock *, Value *> Defines;
+ SmallVector<std::pair<BasicBlock *, Value *>, 4> Defines;
SmallVector<Use *, 4> Uses;
StringRef Name;
Type *Ty;
@@ -49,8 +49,6 @@ class SSAUpdaterBulk {
PredIteratorCache PredCache;
- Value *computeValueAt(BasicBlock *BB, RewriteInfo &R, DominatorTree *DT);
-
public:
explicit SSAUpdaterBulk() = default;
SSAUpdaterBulk(const SSAUpdaterBulk &) = delete;
diff --git a/llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp b/llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp
index 4bb2fb909c113..0e689319b8fac 100644
--- a/llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp
+++ b/llvm/lib/Transforms/Utils/SSAUpdaterBulk.cpp
@@ -53,7 +53,7 @@ void SSAUpdaterBulk::AddAvailableValue(unsigned Var, BasicBlock *BB, Value *V) {
LLVM_DEBUG(dbgs() << "SSAUpdater: Var=" << Var
<< ": added new available value " << *V << " in "
<< BB->getName() << "\n");
- Rewrites[Var].Defines[BB] = V;
+ Rewrites[Var].Defines.emplace_back(BB, V);
}
/// Record a use of the symbolic value. This use will be updated with a
@@ -65,21 +65,6 @@ void SSAUpdaterBulk::AddUse(unsigned Var, Use *U) {
Rewrites[Var].Uses.push_back(U);
}
-// Compute value at the given block BB. We either should already know it, or we
-// should be able to recursively reach it going up dominator tree.
-Value *SSAUpdaterBulk::computeValueAt(BasicBlock *BB, RewriteInfo &R,
- DominatorTree *DT) {
- if (!R.Defines.count(BB)) {
- if (DT->isReachableFromEntry(BB) && PredCache.get(BB).size()) {
- BasicBlock *IDom = DT->getNode(BB)->getIDom()->getBlock();
- Value *V = computeValueAt(IDom, R, DT);
- R.Defines[BB] = V;
- } else
- R.Defines[BB] = UndefValue::get(R.Ty);
- }
- return R.Defines[BB];
-}
-
/// Given sets of UsingBlocks and DefBlocks, compute the set of LiveInBlocks.
/// This is basically a subgraph limited by DefBlocks and UsingBlocks.
static void
@@ -117,11 +102,19 @@ ComputeLiveInBlocks(const SmallPtrSetImpl<BasicBlock *> &UsingBlocks,
}
}
+struct BBValueInfo {
+ Value *LiveInValue = nullptr;
+ Value *LiveOutValue = nullptr;
+};
+
/// Perform all the necessary updates, including new PHI-nodes insertion and the
/// requested uses update.
void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT,
SmallVectorImpl<PHINode *> *InsertedPHIs) {
+ DenseMap<BasicBlock *, BBValueInfo> BBInfos;
for (auto &R : Rewrites) {
+ BBInfos.clear();
+
// Compute locations for new phi-nodes.
// For that we need to initialize DefBlocks from definitions in R.Defines,
// UsingBlocks from uses in R.Uses, then compute LiveInBlocks, and then use
@@ -132,8 +125,8 @@ void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT,
<< " use(s)\n");
SmallPtrSet<BasicBlock *, 2> DefBlocks;
- for (auto &Def : R.Defines)
- DefBlocks.insert(Def.first);
+ for (auto [BB, V] : R.Defines)
+ DefBlocks.insert(BB);
IDF.setDefiningBlocks(DefBlocks);
SmallPtrSet<BasicBlock *, 2> UsingBlocks;
@@ -146,20 +139,52 @@ void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT,
IDF.setLiveInBlocks(LiveInBlocks);
IDF.calculate(IDFBlocks);
+ // Reserve map large enough to reduce growth.
+ BBInfos.init(LiveInBlocks.size() + DefBlocks.size());
+
+ for (auto [BB, V] : R.Defines)
+ BBInfos[BB].LiveOutValue = V;
+
// We've computed IDF, now insert new phi-nodes there.
for (auto *FrontierBB : IDFBlocks) {
IRBuilder<> B(FrontierBB, FrontierBB->begin());
PHINode *PN = B.CreatePHI(R.Ty, 0, R.Name);
- R.Defines[FrontierBB] = PN;
+ BBInfos[FrontierBB].LiveInValue = PN;
if (InsertedPHIs)
InsertedPHIs->push_back(PN);
}
+ // IsLiveOut indicates whether we are computing live-out values (true) or
+ // live-in values (false).
+ std::function<Value *(BasicBlock *, bool)> computeValue =
+ [&](BasicBlock *BB, bool IsLiveOut) -> Value * {
+ auto &BBInfo = BBInfos[BB];
+
+ if (IsLiveOut && BBInfo.LiveOutValue)
+ return BBInfo.LiveOutValue;
+
+ if (BBInfo.LiveInValue)
+ return BBInfo.LiveInValue;
+
+ Value *V = DT->isReachableFromEntry(BB) && PredCache.get(BB).size()
+ ? computeValue(DT->getNode(BB)->getIDom()->getBlock(),
+ /* IsLiveOut = */ true)
+ : UndefValue::get(R.Ty);
+
+ // The call to computeValue for the dominator block can insert another
+ // entry into the map, potentially causing the map to grow and
+ // invalidating the BBInfo reference. Therefore, we need to perform
+ // another map lookup. Simply reserving map size may not be sufficient
+ // as the map could grow further.
+ BBInfos[BB].LiveInValue = V;
+ return V;
+ };
+
// Fill in arguments of the inserted PHIs.
for (auto *BB : IDFBlocks) {
auto *PHI = cast<PHINode>(&BB->front());
for (BasicBlock *Pred : PredCache.get(BB))
- PHI->addIncoming(computeValueAt(Pred, R, DT), Pred);
+ PHI->addIncoming(computeValue(Pred, /* IsLiveOut = */ true), Pred);
}
// Rewrite actual uses with the inserted definitions.
@@ -167,7 +192,10 @@ void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT,
for (Use *U : R.Uses) {
if (!ProcessedUses.insert(U).second)
continue;
- Value *V = computeValueAt(getUserBB(U), R, DT);
+
+ auto *User = cast<Instruction>(U->getUser());
+ BasicBlock *BB = getUserBB(U);
+ Value *V = computeValue(BB, /* IsLiveOut = */ BB != User->getParent());
Value *OldVal = U->get();
assert(OldVal && "Invalid use!");
// Notify that users of the existing value that it is being replaced.
diff --git a/llvm/unittests/Transforms/Utils/SSAUpdaterBulkTest.cpp b/llvm/unittests/Transforms/Utils/SSAUpdaterBulkTest.cpp
index cfd7fbb445840..b97d8ed67a184 100644
--- a/llvm/unittests/Transforms/Utils/SSAUpdaterBulkTest.cpp
+++ b/llvm/unittests/Transforms/Utils/SSAUpdaterBulkTest.cpp
@@ -236,7 +236,7 @@ TEST(SSAUpdaterBulk, SingleBBLoop) {
Loop->dump();
// Output:
// loop: ; preds = %loop, %entry
- // %i.prev = phi i32 [ %i.prev, %loop ], [ 0, %entry ]
+ // %i.prev = phi i32 [ %i, %loop ], [ 0, %entry ]
// %i = add i32 %i.prev, 1
// %cmp = icmp slt i32 %i, 42
// br i1 %cmp, label %loop, label %exit
@@ -246,8 +246,7 @@ TEST(SSAUpdaterBulk, SingleBBLoop) {
PHINode *Phi = Inserted[0];
EXPECT_EQ(Phi, dyn_cast<PHINode>(I->getOperand(0)));
EXPECT_EQ(Phi->getIncomingValueForBlock(Entry), ConstantInt::get(I32Ty, 0));
- EXPECT_NONFATAL_FAILURE(EXPECT_EQ(Phi->getIncomingValueForBlock(Loop), I),
- "Expected equality of these values");
+ EXPECT_EQ(Phi->getIncomingValueForBlock(Loop), I);
}
TEST(SSAUpdaterBulk, TwoBBLoop) {
@@ -298,15 +297,14 @@ TEST(SSAUpdaterBulk, TwoBBLoop) {
// %i.prev = phi i32 [ %i, %loop ], [ 0, %entry ]
// br label %loop
// loop: ; preds = %loop_header
- // %i = add i32 %i, 1
+ // %i = add i32 %i.prev, 1
// %cmp = icmp slt i32 %i, 42
// br i1 %cmp, label %loop_header, label %exit
#endif
ASSERT_EQ(Inserted.size(), 1u);
PHINode *Phi = Inserted[0];
- EXPECT_NONFATAL_FAILURE(EXPECT_EQ(Phi, dyn_cast<PHINode>(I->getOperand(0))),
- "Expected equality of these values");
+ EXPECT_EQ(Phi, dyn_cast<PHINode>(I->getOperand(0)));
EXPECT_EQ(Phi->getParent(), LoopHdr);
EXPECT_EQ(Phi->getIncomingValueForBlock(Entry), ConstantInt::get(I32Ty, 0));
EXPECT_EQ(Phi->getIncomingValueForBlock(Loop), I);
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