[llvm] [SCCP] Support constant structure in PhiNode (PR #163713)
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Thu Oct 16 01:03:11 PDT 2025
https://github.com/aokblast updated https://github.com/llvm/llvm-project/pull/163713
>From 814124cefc1eb03a48dd82954ef6df6eb7011318 Mon Sep 17 00:00:00 2001
From: ShengYi Hung <aokblast at FreeBSD.org>
Date: Wed, 15 Oct 2025 17:57:13 +0800
Subject: [PATCH] [Pass, SCCP] Support constant structure in PhiNode
This patch adds support for constant propagation of individual structure
members through Phi nodes. Each member is handled independently,
allowing optimization opportunities when specific members become constant.
Also, update the testcase since we are able to optimize the call
parameter now.
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 100 ++++++++++++------
.../Transforms/SCCP/constant-range-struct.ll | 66 +++++++++---
2 files changed, 123 insertions(+), 43 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 9693ae6b8ceb5..2f8a6a7909d2e 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -20,6 +20,7 @@
#include "llvm/Analysis/ValueLatticeUtils.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/ConstantRange.h"
+#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
@@ -768,6 +769,7 @@ class SCCPInstVisitor : public InstVisitor<SCCPInstVisitor> {
void handleCallArguments(CallBase &CB);
void handleExtractOfWithOverflow(ExtractValueInst &EVI,
const WithOverflowInst *WO, unsigned Idx);
+ bool isInstUnderDefined(Instruction &Inst);
private:
friend class InstVisitor<SCCPInstVisitor>;
@@ -1383,49 +1385,65 @@ bool SCCPInstVisitor::isEdgeFeasible(BasicBlock *From, BasicBlock *To) const {
// 7. If a conditional branch has a value that is overdefined, make all
// successors executable.
void SCCPInstVisitor::visitPHINode(PHINode &PN) {
- // If this PN returns a struct, just mark the result overdefined.
- // TODO: We could do a lot better than this if code actually uses this.
- if (PN.getType()->isStructTy())
- return (void)markOverdefined(&PN);
-
- if (getValueState(&PN).isOverdefined())
- return; // Quick exit
-
// Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
// and slow us down a lot. Just mark them overdefined.
if (PN.getNumIncomingValues() > 64)
return (void)markOverdefined(&PN);
- unsigned NumActiveIncoming = 0;
+ if (isInstUnderDefined(PN))
+ return;
+ std::vector<unsigned> FeasibleIncomingIndices;
+ for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
+ if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
+ continue;
+ FeasibleIncomingIndices.push_back(i);
+ }
// Look at all of the executable operands of the PHI node. If any of them
// are overdefined, the PHI becomes overdefined as well. If they are all
// constant, and they agree with each other, the PHI becomes the identical
// constant. If they are constant and don't agree, the PHI is a constant
// range. If there are no executable operands, the PHI remains unknown.
- ValueLatticeElement PhiState = getValueState(&PN);
- for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
- if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
- continue;
-
- ValueLatticeElement IV = getValueState(PN.getIncomingValue(i));
- PhiState.mergeIn(IV);
- NumActiveIncoming++;
- if (PhiState.isOverdefined())
- break;
+ if (StructType *STy = dyn_cast<StructType>(PN.getType())) {
+ for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
+ ValueLatticeElement PhiState = getStructValueState(&PN, i);
+ if (PhiState.isOverdefined())
+ continue;
+ for (unsigned j : FeasibleIncomingIndices) {
+ ValueLatticeElement IV = getStructValueState(PN.getIncomingValue(j), i);
+ PhiState.mergeIn(IV);
+ if (PhiState.isOverdefined())
+ break;
+ }
+ mergeInValue(getStructValueState(&PN, i), &PN, PhiState,
+ ValueLatticeElement::MergeOptions().setMaxWidenSteps(
+ FeasibleIncomingIndices.size() + 1));
+ ValueLatticeElement &PhiStateRef = getStructValueState(&PN, i);
+ PhiStateRef.setNumRangeExtensions(
+ std::max((unsigned)FeasibleIncomingIndices.size(),
+ PhiStateRef.getNumRangeExtensions()));
+ }
+ } else {
+ ValueLatticeElement PhiState = getValueState(&PN);
+ for (unsigned i : FeasibleIncomingIndices) {
+ ValueLatticeElement IV = getValueState(PN.getIncomingValue(i));
+ PhiState.mergeIn(IV);
+ if (PhiState.isOverdefined())
+ break;
+ }
+ // We allow up to 1 range extension per active incoming value and one
+ // additional extension. Note that we manually adjust the number of range
+ // extensions to match the number of active incoming values. This helps to
+ // limit multiple extensions caused by the same incoming value, if other
+ // incoming values are equal.
+ mergeInValue(&PN, PhiState,
+ ValueLatticeElement::MergeOptions().setMaxWidenSteps(
+ FeasibleIncomingIndices.size() + 1));
+ ValueLatticeElement &PhiStateRef = getValueState(&PN);
+ PhiStateRef.setNumRangeExtensions(
+ std::max((unsigned)FeasibleIncomingIndices.size(),
+ PhiStateRef.getNumRangeExtensions()));
}
-
- // We allow up to 1 range extension per active incoming value and one
- // additional extension. Note that we manually adjust the number of range
- // extensions to match the number of active incoming values. This helps to
- // limit multiple extensions caused by the same incoming value, if other
- // incoming values are equal.
- mergeInValue(&PN, PhiState,
- ValueLatticeElement::MergeOptions().setMaxWidenSteps(
- NumActiveIncoming + 1));
- ValueLatticeElement &PhiStateRef = getValueState(&PN);
- PhiStateRef.setNumRangeExtensions(
- std::max(NumActiveIncoming, PhiStateRef.getNumRangeExtensions()));
}
void SCCPInstVisitor::visitReturnInst(ReturnInst &I) {
@@ -2125,6 +2143,26 @@ void SCCPInstVisitor::handleCallResult(CallBase &CB) {
}
}
+bool SCCPInstVisitor::isInstUnderDefined(Instruction &Inst) {
+ // For structure Type, we handle each member seperately.
+ // A structure object won't be considered as overDefined when
+ // there is at least one member can become constant.
+ bool IsOverDefined = true;
+ if (StructType *STy = dyn_cast<StructType>(Inst.getType())) {
+ for (unsigned i = 0, e = STy->getNumElements(); i < e; ++i) {
+ ValueLatticeElement PNState = getStructValueState(&Inst, i);
+ IsOverDefined &= PNState.isOverdefined();
+ if (!IsOverDefined)
+ break;
+ }
+ } else {
+ ValueLatticeElement PhiState = getValueState(&Inst);
+ IsOverDefined &= PhiState.isOverdefined();
+ }
+
+ return IsOverDefined;
+}
+
void SCCPInstVisitor::solve() {
// Process the work lists until they are empty!
while (!BBWorkList.empty() || !InstWorkList.empty()) {
diff --git a/llvm/test/Transforms/SCCP/constant-range-struct.ll b/llvm/test/Transforms/SCCP/constant-range-struct.ll
index 7a399df11fb13..46ebdc1b09db8 100644
--- a/llvm/test/Transforms/SCCP/constant-range-struct.ll
+++ b/llvm/test/Transforms/SCCP/constant-range-struct.ll
@@ -25,7 +25,7 @@ true:
br label %exit
false:
- %s.3 = insertvalue {i64, i64} undef, i64 30, 0
+ %s.3 = insertvalue {i64, i64} poison, i64 30, 0
%s.4 = insertvalue {i64, i64} %s.3, i64 300, 1
br label %exit
@@ -39,14 +39,14 @@ define void @struct1_caller() {
; CHECK-NEXT: [[S:%.*]] = call { i64, i64 } @struct1()
; CHECK-NEXT: [[V1:%.*]] = extractvalue { i64, i64 } [[S]], 0
; CHECK-NEXT: [[V2:%.*]] = extractvalue { i64, i64 } [[S]], 1
-; CHECK-NEXT: [[T_1:%.*]] = icmp ne i64 [[V1]], 10
-; CHECK-NEXT: call void @use(i1 [[T_1]])
-; CHECK-NEXT: [[T_2:%.*]] = icmp ult i64 [[V1]], 100
-; CHECK-NEXT: call void @use(i1 [[T_2]])
-; CHECK-NEXT: [[T_3:%.*]] = icmp ne i64 [[V2]], 0
+; CHECK-NEXT: call void @use(i1 true)
+; CHECK-NEXT: call void @use(i1 true)
+; CHECK-NEXT: [[T_3:%.*]] = icmp eq i64 [[V1]], 20
; CHECK-NEXT: call void @use(i1 [[T_3]])
-; CHECK-NEXT: [[T_4:%.*]] = icmp ult i64 [[V2]], 301
-; CHECK-NEXT: call void @use(i1 [[T_4]])
+; CHECK-NEXT: call void @use(i1 true)
+; CHECK-NEXT: call void @use(i1 true)
+; CHECK-NEXT: [[T_6:%.*]] = icmp eq i64 [[V2]], 300
+; CHECK-NEXT: call void @use(i1 [[T_6]])
; CHECK-NEXT: ret void
;
%s = call {i64, i64} @struct1()
@@ -57,10 +57,14 @@ define void @struct1_caller() {
call void @use(i1 %t.1)
%t.2 = icmp ult i64 %v1, 100
call void @use(i1 %t.2)
- %t.3 = icmp ne i64 %v2, 0
+ %t.3 = icmp eq i64 %v1, 20
call void @use(i1 %t.3)
- %t.4 = icmp ult i64 %v2, 301
+ %t.4 = icmp ne i64 %v2, 0
call void @use(i1 %t.4)
+ %t.5 = icmp ult i64 %v2, 301
+ call void @use(i1 %t.5)
+ %t.6 = icmp eq i64 %v2, 300
+ call void @use(i1 %t.6)
ret void
}
@@ -76,7 +80,7 @@ define internal {i64, i64} @struct2() {
; CHECK: exit:
; CHECK-NEXT: [[V1:%.*]] = phi i64 [ 20, [[TRUE]] ], [ 30, [[FALSE]] ]
; CHECK-NEXT: [[V2:%.*]] = phi i64 [ 200, [[TRUE]] ], [ 300, [[FALSE]] ]
-; CHECK-NEXT: [[S_1:%.*]] = insertvalue { i64, i64 } undef, i64 [[V1]], 0
+; CHECK-NEXT: [[S_1:%.*]] = insertvalue { i64, i64 } poison, i64 [[V1]], 0
; CHECK-NEXT: [[S_2:%.*]] = insertvalue { i64, i64 } [[S_1]], i64 [[V2]], 1
; CHECK-NEXT: ret { i64, i64 } [[S_2]]
;
@@ -92,7 +96,7 @@ false:
exit:
%v1 = phi i64 [ 20, %true ], [ 30, %false ]
%v2 = phi i64 [ 200, %true ], [ 300, %false ]
- %s.1 = insertvalue {i64, i64} undef, i64 %v1, 0
+ %s.1 = insertvalue {i64, i64} poison, i64 %v1, 0
%s.2 = insertvalue {i64, i64} %s.1, i64 %v2, 1
ret {i64, i64} %s.2
}
@@ -153,3 +157,41 @@ define void @struct2_caller() {
ret void
}
+
+%"phi_type" = type {i64, i64}
+
+; Function Attrs: mustprogress
+define internal noundef %"phi_type" @test(i32 noundef %input) local_unnamed_addr readnone nounwind {
+; CHECK-LABEL: @test(
+; CHECK-NEXT: br label [[COND_TRUE_I:%.*]]
+; CHECK: cond.true.i:
+; CHECK-NEXT: br label [[COND_END_I:%.*]]
+; CHECK: cond.end.i:
+; CHECK-NEXT: ret [[PHI_TYPE:%.*]] poison
+;
+ %cmp.cond = icmp eq i32 %input, 1
+ br i1 %cmp.cond, label %cond.true.i, label %cond.false.i
+
+cond.true.i:
+ %r1.tmp = insertvalue %"phi_type" poison, i64 1, 0
+ %r1.tmp.2 = insertvalue %"phi_type" %r1.tmp, i64 2, 1
+ br label %cond.end.i
+
+cond.false.i:
+ %r2.tmp = insertvalue %"phi_type" poison, i64 3, 0
+ %r2.tmp.2 = insertvalue %"phi_type" %r2.tmp, i64 4, 1
+ br label %cond.end.i
+
+cond.end.i:
+ %retval = phi %"phi_type" [ %r1.tmp.2, %cond.true.i ], [ %r2.tmp.2, %cond.false.i ]
+ ret %"phi_type" %retval
+}
+
+define dso_local noundef %"phi_type" @test2() {
+; CHECK-LABEL: @test2(
+; CHECK-NEXT: [[CALL_1:%.*]] = tail call fastcc [[PHI_TYPE:%.*]] @[[TEST:[a-zA-Z0-9_$\"\\.-]*[a-zA-Z_$\"\\.-][a-zA-Z0-9_$\"\\.-]*]](i32 noundef 1)
+; CHECK-NEXT: ret [[PHI_TYPE]] { i64 1, i64 2 }
+;
+ %call.1 = tail call fastcc noundef %"phi_type" @test(i32 noundef 1)
+ ret %"phi_type" %call.1
+}
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