[llvm] [PredicateInfo] Support existing `PredicateType` by adding `PredicatePHI` when needing introduction of phi nodes (PR #151132)
Rajveer Singh Bharadwaj via llvm-commits
llvm-commits at lists.llvm.org
Sat Aug 9 04:21:15 PDT 2025
https://github.com/Rajveer100 updated https://github.com/llvm/llvm-project/pull/151132
>From 5557a40f8c6f004627182139637a6920429c07f1 Mon Sep 17 00:00:00 2001
From: Rajveer <rajveer.developer at icloud.com>
Date: Tue, 29 Jul 2025 17:21:36 +0530
Subject: [PATCH] [PredicateInfo] Support existing `PredicateType` by adding
`PredicatePHI` when needing introduction of phi nodes
Resolves #150606
Currently `ssa.copy` is used mostly for straight line code, i.e, without
joins or uses of phi nodes. With this, passes would be able to pick up the
relevant info and further optimize the IR.
---
.../llvm/Transforms/Utils/PredicateInfo.h | 15 +-
llvm/lib/Transforms/Utils/PredicateInfo.cpp | 148 ++++++++++++++++++
.../Util/PredicateInfo/phi-predicate.ll | 46 ++++++
3 files changed, 208 insertions(+), 1 deletion(-)
create mode 100644 llvm/test/Transforms/Util/PredicateInfo/phi-predicate.ll
diff --git a/llvm/include/llvm/Transforms/Utils/PredicateInfo.h b/llvm/include/llvm/Transforms/Utils/PredicateInfo.h
index c243e236901d5..6832f31e558c4 100644
--- a/llvm/include/llvm/Transforms/Utils/PredicateInfo.h
+++ b/llvm/include/llvm/Transforms/Utils/PredicateInfo.h
@@ -67,7 +67,7 @@ class Value;
class IntrinsicInst;
class raw_ostream;
-enum PredicateType { PT_Branch, PT_Assume, PT_Switch };
+enum PredicateType { PT_Branch, PT_Assume, PT_Switch, PT_PHI };
/// Constraint for a predicate of the form "cmp Pred Op, OtherOp", where Op
/// is the value the constraint applies to (the ssa.copy result).
@@ -171,6 +171,19 @@ class PredicateSwitch : public PredicateWithEdge {
}
};
+class PredicatePHI : public PredicateBase {
+public:
+ BasicBlock *PHIBlock;
+ SmallVector<std::pair<BasicBlock *, PredicateBase *>, 4> IncomingPredicates;
+
+ PredicatePHI(Value *Op, BasicBlock *PHIBB)
+ : PredicateBase(PT_PHI, Op, nullptr), PHIBlock(PHIBB) {}
+ PredicatePHI() = delete;
+ static bool classof(const PredicateBase *PB) { return PB->Type == PT_PHI; }
+
+ LLVM_ABI std::optional<PredicateConstraint> getConstraint() const;
+};
+
/// Encapsulates PredicateInfo, including all data associated with memory
/// accesses.
class PredicateInfo {
diff --git a/llvm/lib/Transforms/Utils/PredicateInfo.cpp b/llvm/lib/Transforms/Utils/PredicateInfo.cpp
index de9deab28750f..b6b6055ac3e35 100644
--- a/llvm/lib/Transforms/Utils/PredicateInfo.cpp
+++ b/llvm/lib/Transforms/Utils/PredicateInfo.cpp
@@ -15,7 +15,9 @@
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/IteratedDominanceFrontier.h"
#include "llvm/IR/AssemblyAnnotationWriter.h"
+#include "llvm/IR/CFG.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
@@ -213,6 +215,8 @@ class PredicateInfoBuilder {
// whether it returned a valid result.
DenseMap<Value *, unsigned int> ValueInfoNums;
+ DenseMap<BasicBlock *, SmallVector<Value *, 4>> PHICandidates;
+
BumpPtrAllocator &Allocator;
ValueInfo &getOrCreateValueInfo(Value *);
@@ -224,6 +228,13 @@ class PredicateInfoBuilder {
SmallVectorImpl<Value *> &OpsToRename);
void processSwitch(SwitchInst *, BasicBlock *,
SmallVectorImpl<Value *> &OpsToRename);
+ void identifyPHICandidates(SmallVectorImpl<Value *> &OpsToRename);
+ void needsPHIInsertion(Value *Op,
+ const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks,
+ SmallPtrSetImpl<BasicBlock *> &PHIBlocks);
+ void insertPredicatePHIs(Value *Op, BasicBlock *PHIBlock,
+ SmallVectorImpl<Value *> &OpsToRename);
+ void processPredicatePHIs(SmallVectorImpl<Value *> &OpsToRename);
void renameUses(SmallVectorImpl<Value *> &OpsToRename);
void addInfoFor(SmallVectorImpl<Value *> &OpsToRename, Value *Op,
PredicateBase *PB);
@@ -452,6 +463,99 @@ void PredicateInfoBuilder::processSwitch(
}
}
+void PredicateInfoBuilder::identifyPHICandidates(
+ SmallVectorImpl<Value *> &OpsToRename) {
+ for (Value *Op : OpsToRename) {
+ const auto &ValueInfo = getValueInfo(Op);
+ SmallPtrSet<BasicBlock *, 4> DefiningBlocks;
+ for (const auto *PInfo : ValueInfo.Infos) {
+ if (auto *PBranch = dyn_cast<PredicateBranch>(PInfo)) {
+ DefiningBlocks.insert(PBranch->From);
+ } else if (auto *PSwitch = dyn_cast<PredicateSwitch>(PInfo)) {
+ DefiningBlocks.insert(PSwitch->From);
+ }
+ }
+
+ if (DefiningBlocks.size() > 1) {
+ SmallPtrSet<BasicBlock *, 8> PHIBlocks;
+ needsPHIInsertion(Op, DefiningBlocks, PHIBlocks);
+ for (BasicBlock *PHIBlock : PHIBlocks) {
+ PHICandidates[PHIBlock].push_back(Op);
+ }
+ }
+ }
+}
+
+void PredicateInfoBuilder::needsPHIInsertion(
+ Value *Op, const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks,
+ SmallPtrSetImpl<BasicBlock *> &PHIBlocks) {
+ IDFCalculator<false> IDF(DT);
+ IDF.setDefiningBlocks(DefiningBlocks);
+
+ SmallPtrSet<BasicBlock *, 8> LiveInBlocks;
+ for (const auto &DefBlock : DefiningBlocks) {
+ for (BasicBlock *Succ : successors(DefBlock)) {
+ for (Instruction &I : *Succ) {
+ if (isa<StoreInst>(&I) || isa<LoadInst>(&I)) {
+ LiveInBlocks.insert(Succ);
+ }
+ }
+ }
+ }
+ IDF.setLiveInBlocks(LiveInBlocks);
+
+ SmallVector<BasicBlock *, 4> IDFBlocks;
+ IDF.calculate(IDFBlocks);
+
+ for (const auto &IDFBlock : IDFBlocks) {
+ PHIBlocks.insert(std::move(IDFBlock));
+ }
+}
+
+void PredicateInfoBuilder::insertPredicatePHIs(
+ Value *Op, BasicBlock *PHIBlock, SmallVectorImpl<Value *> &OpsToRename) {
+ IRBuilder<> Builder(&PHIBlock->front());
+
+ PHINode *PHI = Builder.CreatePHI(Op->getType(), pred_size(PHIBlock),
+ Op->getName() + ".predicate.phi");
+ PredicatePHI *PPHI = new (Allocator) PredicatePHI(Op, PHIBlock);
+
+ PPHI->RenamedOp = PHI;
+
+ const auto &ValueInfo = getValueInfo(Op);
+ for (BasicBlock *Pred : predecessors(PHIBlock)) {
+ Value *IncomingValue = Op;
+ for (const auto *PInfo : ValueInfo.Infos) {
+ if (auto *PBranch = dyn_cast<PredicateBranch>(PInfo)) {
+ if (PBranch->From == Pred && PBranch->To == PHIBlock) {
+ PPHI->IncomingPredicates.push_back(
+ {Pred, const_cast<PredicateBase *>(PInfo)});
+ IncomingValue = PBranch->OriginalOp;
+ }
+ } else if (auto *PSwitch = dyn_cast<PredicateSwitch>(PInfo)) {
+ if (PSwitch->From == Pred && PSwitch->To == PHIBlock) {
+ PPHI->IncomingPredicates.push_back(
+ {Pred, const_cast<PredicateBase *>(PInfo)});
+ IncomingValue = PSwitch->OriginalOp;
+ }
+ }
+ }
+ PHI->addIncoming(IncomingValue, Pred);
+ }
+
+ addInfoFor(OpsToRename, Op, PPHI);
+}
+
+void PredicateInfoBuilder::processPredicatePHIs(
+ SmallVectorImpl<Value *> &OpsToRename) {
+ for (const auto &PHICandidate : PHICandidates) {
+ BasicBlock *PHIBlock = PHICandidate.first;
+ for (Value *Op : PHICandidate.second) {
+ insertPredicatePHIs(Op, PHIBlock, OpsToRename);
+ }
+ }
+}
+
// Build predicate info for our function
void PredicateInfoBuilder::buildPredicateInfo() {
DT.updateDFSNumbers();
@@ -478,6 +582,10 @@ void PredicateInfoBuilder::buildPredicateInfo() {
if (DT.isReachableFromEntry(II->getParent()))
processAssume(II, II->getParent(), OpsToRename);
}
+
+ identifyPHICandidates(OpsToRename);
+ processPredicatePHIs(OpsToRename);
+
// Now rename all our operations.
renameUses(OpsToRename);
}
@@ -535,6 +643,12 @@ Value *PredicateInfoBuilder::materializeStack(unsigned int &Counter,
CreateSSACopy(B, Op, Op->getName() + "." + Twine(Counter++));
PI.PredicateMap.insert({PIC, ValInfo});
Result.Def = PIC;
+ } else if (isa<PredicatePHI>(ValInfo)) {
+ auto *PPHI = dyn_cast<PredicatePHI>(ValInfo);
+ IRBuilder<> B(&*PPHI->PHIBlock->getFirstInsertionPt());
+ CallInst *PIC = CreateSSACopy(B, Op);
+ PI.PredicateMap.insert({PIC, ValInfo});
+ Result.Def = PIC;
} else {
auto *PAssume = dyn_cast<PredicateAssume>(ValInfo);
assert(PAssume &&
@@ -623,6 +737,15 @@ void PredicateInfoBuilder::renameUses(SmallVectorImpl<Value *> &OpsToRename) {
OrderedUses.push_back(VD);
}
}
+ } else if (const auto *PPHI = dyn_cast<PredicatePHI>(PossibleCopy)) {
+ VD.LocalNum = LN_First;
+ auto *DomNode = DT.getNode(PPHI->PHIBlock);
+ if (DomNode) {
+ VD.DFSIn = DomNode->getDFSNumIn();
+ VD.DFSOut = DomNode->getDFSNumOut();
+ VD.PInfo = PossibleCopy;
+ OrderedUses.push_back(VD);
+ }
}
}
@@ -773,10 +896,31 @@ std::optional<PredicateConstraint> PredicateBase::getConstraint() const {
}
return {{CmpInst::ICMP_EQ, cast<PredicateSwitch>(this)->CaseValue}};
+ case PT_PHI:
+ return cast<PredicatePHI>(this)->getConstraint();
}
llvm_unreachable("Unknown predicate type");
}
+std::optional<PredicateConstraint> PredicatePHI::getConstraint() const {
+ if (IncomingPredicates.empty())
+ return std::nullopt;
+
+ auto FirstConstraint = IncomingPredicates[0].second->getConstraint();
+ if (!FirstConstraint)
+ return std::nullopt;
+
+ for (size_t I = 1; I < IncomingPredicates.size(); ++I) {
+ auto Constraint = IncomingPredicates[I].second->getConstraint();
+ if (!Constraint || Constraint->Predicate != FirstConstraint->Predicate ||
+ Constraint->OtherOp != FirstConstraint->OtherOp) {
+ return std::nullopt;
+ }
+ }
+
+ return FirstConstraint;
+}
+
void PredicateInfo::verifyPredicateInfo() const {}
// Replace ssa_copy calls created by PredicateInfo with their operand.
@@ -838,6 +982,10 @@ class PredicateInfoAnnotatedWriter : public AssemblyAnnotationWriter {
} else if (const auto *PA = dyn_cast<PredicateAssume>(PI)) {
OS << "; assume predicate info {"
<< " Comparison:" << *PA->Condition;
+ } else if (const auto *PP = dyn_cast<PredicatePHI>(PI)) {
+ OS << "; phi predicate info { PHIBlock: ";
+ PP->PHIBlock->printAsOperand(OS);
+ OS << " IncomingEdges: " << PP->IncomingPredicates.size();
}
OS << ", RenamedOp: ";
PI->RenamedOp->printAsOperand(OS, false);
diff --git a/llvm/test/Transforms/Util/PredicateInfo/phi-predicate.ll b/llvm/test/Transforms/Util/PredicateInfo/phi-predicate.ll
new file mode 100644
index 0000000000000..7663455ca89a1
--- /dev/null
+++ b/llvm/test/Transforms/Util/PredicateInfo/phi-predicate.ll
@@ -0,0 +1,46 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes=print-predicateinfo < %s 2>&1 >/dev/null | FileCheck %s
+
+ at p = local_unnamed_addr global i32 0
+
+define noundef i32 @h5diff(i32 %0, i1 %1) local_unnamed_addr #0 {
+; CHECK-LABEL: @h5diff(
+; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[TMP0:%.*]], 0
+; CHECK-NEXT: br i1 [[TMP1:%.*]], label [[TMP3:%.*]], label [[TMP4:%.*]]
+; CHECK: 3:
+; CHECK-NEXT: store i32 1, ptr @p, align 4
+; CHECK: [[COND_0:%.*]] = call i1 @llvm.ssa.copy.i1(i1 [[COND]])
+; CHECK: [[DOT0:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[TMP0]])
+; CHECK-NEXT: br i1 [[COND]], label [[TMP5:%.*]], label [[COMMON_RET:%.*]]
+; CHECK: common.ret:
+; CHECK-NEXT: ret i32 0
+; CHECK: 4:
+; CHECK-NEXT: store i32 2, ptr @p, align 4
+; CHECK: [[COND_1:%.*]] = call i1 @llvm.ssa.copy.i1(i1 [[COND]])
+; CHECK: [[DOT1:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[TMP0]])
+; CHECK-NEXT: br i1 [[COND]], label [[TMP5]], label [[COMMON_RET]]
+; CHECK: 5:
+; CHECK-NEXT: [[DOTPREDICATE_PHI:%.*]] = phi i32 [ [[DOT1]], [[TMP4]] ], [ [[DOT0]], [[TMP3]] ]
+; CHECK-NEXT: [[COND_PREDICATE_PHI:%.*]] = phi i1 [ [[COND_1]], [[TMP4]] ], [ [[COND_0]], [[TMP3]] ]
+; CHECK: [[TMP6:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[TMP0]])
+; CHECK-NEXT: store i32 [[TMP6]], ptr @p, align 4
+; CHECK-NEXT: br label [[COMMON_RET]]
+;
+ %cond = icmp eq i32 %0, 0
+ br i1 %1, label %3, label %4
+
+3:
+ store i32 1, ptr @p, align 4
+ br i1 %cond, label %5, label %common.ret
+
+common.ret:
+ ret i32 0
+
+4:
+ store i32 2, ptr @p, align 4
+ br i1 %cond, label %5, label %common.ret
+
+5:
+ store i32 %0, ptr @p, align 4
+ br label %common.ret
+}
More information about the llvm-commits
mailing list