[llvm] [IR] Change PHINode::removeIncomingValueIf() to loop incoming values backwards (PR #173444)
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Tue Dec 23 20:00:28 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-ir
Author: Mingjie Xu (Enna1)
<details>
<summary>Changes</summary>
See discussion in https://github.com/llvm/llvm-project/pull/172639#issuecomment-3686893143
If someone did `PN->removeIncomingValueIf([](unsigned Idx) { return Idx == 0; })` to remove the first incoming value, current implementation will remove all incoming values.
There are purely index based predicate use cases in:
- https://github.com/llvm/llvm-project/blob/8c5a0f74a12d69d2fb7d6ed59f91759f18273bcd/llvm/lib/Transforms/Utils/LoopSimplify.cpp#L429
- https://github.com/llvm/llvm-project/blob/8c5a0f74a12d69d2fb7d6ed59f91759f18273bcd/llvm/lib/Transforms/Utils/LoopUtils.cpp#L562
This patch makes `PHINode::removeIncomingValueIf()` to loop incoming values backwards, to ensure `PHINode::removeIncomingValueIf()` working as expected.
---
Full diff: https://github.com/llvm/llvm-project/pull/173444.diff
3 Files Affected:
- (modified) llvm/lib/IR/Instructions.cpp (+4-5)
- (modified) llvm/test/Transforms/DFAJumpThreading/dfa-unfold-select.ll (+9-9)
- (modified) llvm/test/Transforms/JumpThreading/select.ll (+1-1)
``````````diff
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 980693a941384..f64cab7309cff 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -160,18 +160,17 @@ Value *PHINode::removeIncomingValue(unsigned Idx, bool DeletePHIIfEmpty) {
void PHINode::removeIncomingValueIf(function_ref<bool(unsigned)> Predicate,
bool DeletePHIIfEmpty) {
unsigned NumOps = getNumIncomingValues();
- unsigned Idx = 0;
- while (Idx < NumOps) {
+
+ // Loop backwards in case the predicate is purely index based.
+ for (int Idx = NumOps - 1; Idx >= 0; --Idx) {
if (Predicate(Idx)) {
- unsigned LastIdx = NumOps - 1;
+ int LastIdx = NumOps - 1;
if (Idx != LastIdx) {
setIncomingValue(Idx, getIncomingValue(LastIdx));
setIncomingBlock(Idx, getIncomingBlock(LastIdx));
}
getOperandUse(LastIdx).set(nullptr);
NumOps--;
- } else {
- Idx++;
}
}
diff --git a/llvm/test/Transforms/DFAJumpThreading/dfa-unfold-select.ll b/llvm/test/Transforms/DFAJumpThreading/dfa-unfold-select.ll
index 5f0ad6bb1c070..4e253915930c0 100644
--- a/llvm/test/Transforms/DFAJumpThreading/dfa-unfold-select.ll
+++ b/llvm/test/Transforms/DFAJumpThreading/dfa-unfold-select.ll
@@ -173,7 +173,7 @@ define i32 @test2(i32 %num) {
; CHECK-NEXT: br i1 [[CMP_EXIT_JT3]], label [[FOR_BODY_JT3]], label [[FOR_END]]
; CHECK: for.inc.jt2:
; CHECK-NEXT: [[COUNT9:%.*]] = phi i32 [ [[COUNT5]], [[STATE2_2_SI_UNFOLD_FALSE_JT2]] ], [ [[COUNT6]], [[STATE1_1_SI_UNFOLD_FALSE_JT2]] ]
-; CHECK-NEXT: [[STATE_NEXT_JT2]] = phi i32 [ [[STATE2_1_SI_UNFOLD_PHI_JT2]], [[STATE2_2_SI_UNFOLD_FALSE_JT2]] ], [ [[DOTSI_UNFOLD_PHI4_JT2]], [[STATE1_1_SI_UNFOLD_FALSE_JT2]] ]
+; CHECK-NEXT: [[STATE_NEXT_JT2]] = phi i32 [ [[DOTSI_UNFOLD_PHI4_JT2]], [[STATE1_1_SI_UNFOLD_FALSE_JT2]] ], [ [[STATE2_1_SI_UNFOLD_PHI_JT2]], [[STATE2_2_SI_UNFOLD_FALSE_JT2]] ]
; CHECK-NEXT: [[INC_JT2]] = add nsw i32 [[COUNT9]], 1
; CHECK-NEXT: [[CMP_EXIT_JT2:%.*]] = icmp slt i32 [[INC_JT2]], [[NUM]]
; CHECK-NEXT: br i1 [[CMP_EXIT_JT2]], label [[FOR_BODY_JT2]], label [[FOR_END]]
@@ -262,7 +262,7 @@ define i32 @test3(i32 %num) {
; CHECK-NEXT: [[SEL_2_SI_UNFOLD_PHI:%.*]] = phi i32 [ poison, [[SEL_2_SI_UNFOLD_FALSE:%.*]] ], [ poison, [[SEL_2_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: br label [[FOR_INC]]
; CHECK: sel.3.si.unfold.false.jt4:
-; CHECK-NEXT: [[SEL_2_SI_UNFOLD_PHI_JT3:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI_JT3]], [[SEL_2_SI_UNFOLD_TRUE_JT3]] ], [ [[DOTSI_UNFOLD_PHI1_JT4]], [[SEL_2_SI_UNFOLD_FALSE_JT4]] ]
+; CHECK-NEXT: [[SEL_2_SI_UNFOLD_PHI_JT3:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI1_JT4]], [[SEL_2_SI_UNFOLD_FALSE_JT4]] ], [ [[DOTSI_UNFOLD_PHI_JT3]], [[SEL_2_SI_UNFOLD_TRUE_JT3]] ]
; CHECK-NEXT: br label [[FOR_INC_JT3]]
; CHECK: sel.1.si.unfold.true:
; CHECK-NEXT: br i1 [[CMP_1]], label [[FOR_INC]], label [[SEL_1_SI_UNFOLD_FALSE_JT2:%.*]]
@@ -286,13 +286,13 @@ define i32 @test3(i32 %num) {
; CHECK-NEXT: br i1 [[CMP_EXIT_JT3]], label [[FOR_BODY_JT3:%.*]], label [[FOR_END]]
; CHECK: for.inc.jt1:
; CHECK-NEXT: [[COUNT4:%.*]] = phi i32 [ [[COUNT_JT3]], [[FOR_BODY_JT3]] ], [ [[COUNT5]], [[SEL_1_SI_UNFOLD_TRUE_JT1]] ], [ [[COUNT]], [[FOR_BODY]] ]
-; CHECK-NEXT: [[STATE_NEXT_JT1]] = phi i32 [ [[DOTSI_UNFOLD_PHI2_JT1]], [[SEL_1_SI_UNFOLD_TRUE_JT1]] ], [ 1, [[FOR_BODY]] ], [ 1, [[FOR_BODY_JT3]] ]
+; CHECK-NEXT: [[STATE_NEXT_JT1]] = phi i32 [ 1, [[FOR_BODY_JT3]] ], [ 1, [[FOR_BODY]] ], [ [[DOTSI_UNFOLD_PHI2_JT1]], [[SEL_1_SI_UNFOLD_TRUE_JT1]] ]
; CHECK-NEXT: [[INC_JT1]] = add nsw i32 [[COUNT4]], 1
; CHECK-NEXT: [[CMP_EXIT_JT1:%.*]] = icmp slt i32 [[INC_JT1]], [[NUM]]
; CHECK-NEXT: br i1 [[CMP_EXIT_JT1]], label [[FOR_BODY_JT1]], label [[FOR_END]]
; CHECK: for.inc.jt2:
; CHECK-NEXT: [[COUNT7:%.*]] = phi i32 [ [[COUNT6]], [[CASE1]] ], [ [[COUNT5]], [[SEL_1_SI_UNFOLD_FALSE_JT2]] ]
-; CHECK-NEXT: [[STATE_NEXT_JT2]] = phi i32 [ [[DOTSI_UNFOLD_PHI3_JT2]], [[SEL_1_SI_UNFOLD_FALSE_JT2]] ], [ 2, [[CASE1]] ]
+; CHECK-NEXT: [[STATE_NEXT_JT2]] = phi i32 [ 2, [[CASE1]] ], [ [[DOTSI_UNFOLD_PHI3_JT2]], [[SEL_1_SI_UNFOLD_FALSE_JT2]] ]
; CHECK-NEXT: [[INC_JT2]] = add nsw i32 [[COUNT7]], 1
; CHECK-NEXT: [[CMP_EXIT_JT2:%.*]] = icmp slt i32 [[INC_JT2]], [[NUM]]
; CHECK-NEXT: br i1 [[CMP_EXIT_JT2]], label [[FOR_BODY_JT2]], label [[FOR_END]]
@@ -406,8 +406,8 @@ define void @pr65222(i32 %flags, i1 %cmp, i1 %tobool.not) {
; CHECK-NEXT: [[OTHER_JT0:%.*]] = phi i32 [ 0, [[TOUNFOLD_SI_UNFOLD_FALSE_JT0]] ]
; CHECK-NEXT: br label [[SW_BB]]
; CHECK: if.end.jt1:
-; CHECK-NEXT: [[UNFOLDED_JT1:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI2]], [[COND1_SI_UNFOLD_TRUE]] ], [ [[COND_SI_UNFOLD_PHI_JT1]], [[TOUNFOLD_SI_UNFOLD_FALSE_JT1]] ], [ [[DOTSI_UNFOLD_PHI3_JT1]], [[COND1_SI_UNFOLD_FALSE_JT1]] ]
-; CHECK-NEXT: [[OTHER_JT1:%.*]] = phi i32 [ 0, [[COND1_SI_UNFOLD_TRUE]] ], [ 0, [[TOUNFOLD_SI_UNFOLD_FALSE_JT1]] ], [ 0, [[COND1_SI_UNFOLD_FALSE_JT1]] ]
+; CHECK-NEXT: [[UNFOLDED_JT1:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI2]], [[COND1_SI_UNFOLD_TRUE]] ], [ [[DOTSI_UNFOLD_PHI3_JT1]], [[COND1_SI_UNFOLD_FALSE_JT1]] ], [ [[COND_SI_UNFOLD_PHI_JT1]], [[TOUNFOLD_SI_UNFOLD_FALSE_JT1]] ]
+; CHECK-NEXT: [[OTHER_JT1:%.*]] = phi i32 [ 0, [[COND1_SI_UNFOLD_TRUE]] ], [ 0, [[COND1_SI_UNFOLD_FALSE_JT1]] ], [ 0, [[TOUNFOLD_SI_UNFOLD_FALSE_JT1]] ]
; CHECK-NEXT: br label [[UNREACHABLE]]
; CHECK: unreachable:
; CHECK-NEXT: unreachable
@@ -462,7 +462,7 @@ define i16 @pr160250() {
; CHECK-NEXT: [[DOT5_SI_UNFOLD_PHI:%.*]] = phi i32 [ poison, [[DOT5_SI_UNFOLD_FALSE:%.*]] ], [ poison, [[DOT5_SI_UNFOLD_TRUE1]] ]
; CHECK-NEXT: br i1 false, label [[SPEC_SELECT_SI_UNFOLD_FALSE1:%.*]], label [[SPEC_SELECT1_SI_UNFOLD_FALSE_JT1:%.*]]
; CHECK: spec.select1.si.unfold.true.jt0:
-; CHECK-NEXT: [[DOT5_SI_UNFOLD_PHI_JT0:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI1]], [[DOT5_SI_UNFOLD_TRUE]] ], [ [[DOTSI_UNFOLD_PHI2_JT0]], [[DOT5_SI_UNFOLD_FALSE_JT0]] ]
+; CHECK-NEXT: [[DOT5_SI_UNFOLD_PHI_JT0:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI2_JT0]], [[DOT5_SI_UNFOLD_FALSE_JT0]] ], [ [[DOTSI_UNFOLD_PHI1]], [[DOT5_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: br i1 false, label [[SPEC_SELECT_SI_UNFOLD_FALSE:%.*]], label [[SPEC_SELECT1_SI_UNFOLD_FALSE_JT1]]
; CHECK: spec.select1.si.unfold.false:
; CHECK-NEXT: br label [[SPEC_SELECT_SI_UNFOLD_FALSE1]]
@@ -473,7 +473,7 @@ define i16 @pr160250() {
; CHECK-NEXT: [[SPEC_SELECT1_SI_UNFOLD_PHI:%.*]] = phi i32 [ poison, [[SPEC_SELECT1_SI_UNFOLD_FALSE:%.*]] ], [ [[DOT5_SI_UNFOLD_PHI]], [[SPEC_SELECT1_SI_UNFOLD_TRUE1]] ]
; CHECK-NEXT: br label [[CLEANUP87:%.*]]
; CHECK: spec.select.si.unfold.false.jt0:
-; CHECK-NEXT: [[SPEC_SELECT1_SI_UNFOLD_PHI_JT0:%.*]] = phi i32 [ [[DOT5_SI_UNFOLD_PHI_JT0]], [[SPEC_SELECT1_SI_UNFOLD_TRUE]] ], [ [[DOTSI_UNFOLD_PHI_JT0]], [[SPEC_SELECT1_SI_UNFOLD_FALSE_JT1]] ]
+; CHECK-NEXT: [[SPEC_SELECT1_SI_UNFOLD_PHI_JT0:%.*]] = phi i32 [ [[DOTSI_UNFOLD_PHI_JT0]], [[SPEC_SELECT1_SI_UNFOLD_FALSE_JT1]] ], [ [[DOT5_SI_UNFOLD_PHI_JT0]], [[SPEC_SELECT1_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: br label [[CLEANUP87_JT0]]
; CHECK: .6.si.unfold.true:
; CHECK-NEXT: br i1 false, label [[CLEANUP87]], label [[DOT6_SI_UNFOLD_FALSE_JT0:%.*]]
@@ -492,7 +492,7 @@ define i16 @pr160250() {
; CHECK-NEXT: i32 1, label [[FOR_COND48_BACKEDGE]]
; CHECK-NEXT: ]
; CHECK: cleanup87.jt0:
-; CHECK-NEXT: [[CLEANUP_DEST_SLOT_3_JT0:%.*]] = phi i32 [ 0, [[FOR_COND48]] ], [ [[DOTSI_UNFOLD_PHI3]], [[DOT6_SI_UNFOLD_TRUE]] ], [ [[SPEC_SELECT1_SI_UNFOLD_PHI_JT0]], [[SPEC_SELECT_SI_UNFOLD_FALSE]] ], [ [[DOTSI_UNFOLD_PHI4_JT0]], [[DOT6_SI_UNFOLD_FALSE_JT0]] ]
+; CHECK-NEXT: [[CLEANUP_DEST_SLOT_3_JT0:%.*]] = phi i32 [ 0, [[FOR_COND48]] ], [ [[DOTSI_UNFOLD_PHI4_JT0]], [[DOT6_SI_UNFOLD_FALSE_JT0]] ], [ [[SPEC_SELECT1_SI_UNFOLD_PHI_JT0]], [[SPEC_SELECT_SI_UNFOLD_FALSE]] ], [ [[DOTSI_UNFOLD_PHI3]], [[DOT6_SI_UNFOLD_TRUE]] ]
; CHECK-NEXT: br label [[FOR_COND48_BACKEDGE]]
; CHECK: for.cond48.backedge:
; CHECK-NEXT: br label [[FOR_COND48]]
diff --git a/llvm/test/Transforms/JumpThreading/select.ll b/llvm/test/Transforms/JumpThreading/select.ll
index 03a87f93c3722..4ec55a66bb8ac 100644
--- a/llvm/test/Transforms/JumpThreading/select.ll
+++ b/llvm/test/Transforms/JumpThreading/select.ll
@@ -446,7 +446,7 @@ define i32 @unfold4(i32 %u, i32 %v, i32 %w, i32 %x, i32 %y, i32 %z, i32 %j) noun
; CHECK: .exit.thread:
; CHECK-NEXT: br label [[DOTEXIT_THREAD5]]
; CHECK: .exit.thread5:
-; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ [[J]], [[DOTEXIT_THREAD]] ], [ [[ADD3]], [[DOTEXIT]] ], [ [[ADD3]], [[COND_FALSE_10_I]] ], [ [[ADD3]], [[COND_FALSE_I]] ]
+; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ [[J]], [[DOTEXIT_THREAD]] ], [ [[ADD3]], [[DOTEXIT]] ], [ [[ADD3]], [[COND_FALSE_I]] ], [ [[ADD3]], [[COND_FALSE_10_I]] ]
; CHECK-NEXT: ret i32 [[TMP0]]
;
entry:
``````````
</details>
https://github.com/llvm/llvm-project/pull/173444
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