[llvm] [LoopInterchange] Fix handling of PHI which refers to another PHI (PR #194364)
Ryotaro Kasuga via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 28 07:38:07 PDT 2026
https://github.com/kasuga-fj updated https://github.com/llvm/llvm-project/pull/194364
>From bcffec37dfea5363d2fcf4b25ea100bc20c8a414 Mon Sep 17 00:00:00 2001
From: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
Date: Mon, 27 Apr 2026 13:05:01 +0000
Subject: [PATCH 1/2] [LoopInterchange] Fix handling of PHI which referes to
another PHI
---
.../lib/Transforms/Scalar/LoopInterchange.cpp | 14 ++---
.../Transforms/LoopInterchange/phi-to-phi.ll | 62 +++++++++++++++++++
2 files changed, 69 insertions(+), 7 deletions(-)
create mode 100644 llvm/test/Transforms/LoopInterchange/phi-to-phi.ll
diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index 49a9e77ef8deb..1c249d5b9fb87 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -1935,7 +1935,6 @@ bool LoopInterchangeTransform::transform(
reduction2Memory();
if (InnerLoop->getSubLoops().empty()) {
- BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
LLVM_DEBUG(dbgs() << "Splitting the inner loop latch\n");
auto &InductionPHIs = LIL.getInnerLoopInductions();
if (InductionPHIs.empty()) {
@@ -1945,12 +1944,13 @@ bool LoopInterchangeTransform::transform(
SmallVector<Instruction *, 8> InnerIndexVarList;
for (PHINode *CurInductionPHI : InductionPHIs) {
- if (CurInductionPHI->getIncomingBlock(0) == InnerLoopPreHeader)
- InnerIndexVarList.push_back(
- dyn_cast<Instruction>(CurInductionPHI->getIncomingValue(1)));
- else
- InnerIndexVarList.push_back(
- dyn_cast<Instruction>(CurInductionPHI->getIncomingValue(0)));
+ Instruction *IncomingValue = dyn_cast<Instruction>(
+ CurInductionPHI->getIncomingValueForBlock(InnerLoop->getLoopLatch()));
+ if (any_of(InductionPHIs, [IncomingValue](PHINode *InductionPHI) {
+ return IncomingValue == InductionPHI;
+ }))
+ continue;
+ InnerIndexVarList.push_back(IncomingValue);
}
// Create a new latch block for the inner loop. We split at the
diff --git a/llvm/test/Transforms/LoopInterchange/phi-to-phi.ll b/llvm/test/Transforms/LoopInterchange/phi-to-phi.ll
new file mode 100644
index 0000000000000..8fb336e1cac88
--- /dev/null
+++ b/llvm/test/Transforms/LoopInterchange/phi-to-phi.ll
@@ -0,0 +1,62 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -passes=loop-interchange -loop-interchange-profitabilities=ignore -verify-dom-info -verify-loop-info -verify-scev -verify-loop-lcssa -S | FileCheck %s
+
+; Check that `%k`, which refers to another phi node, is processed correctly.
+
+define void @f(ptr %A) {
+; CHECK-LABEL: define void @f(
+; CHECK-SAME: ptr [[A:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: br label %[[INNER_PREHEADER:.*]]
+; CHECK: [[OUTER_HEADER_PREHEADER:.*]]:
+; CHECK-NEXT: br label %[[OUTER_HEADER:.*]]
+; CHECK: [[OUTER_HEADER]]:
+; CHECK-NEXT: [[I:%.*]] = phi i64 [ [[I_INC:%.*]], %[[OUTER_LATCH:.*]] ], [ 0, %[[OUTER_HEADER_PREHEADER]] ]
+; CHECK-NEXT: br label %[[INNER_SPLIT1:.*]]
+; CHECK: [[INNER_PREHEADER]]:
+; CHECK-NEXT: br label %[[INNER:.*]]
+; CHECK: [[INNER]]:
+; CHECK-NEXT: [[J:%.*]] = phi i64 [ [[TMP0:%.*]], %[[INNER_SPLIT:.*]] ], [ 0, %[[INNER_PREHEADER]] ]
+; CHECK-NEXT: [[K:%.*]] = phi i64 [ [[J]], %[[INNER_SPLIT]] ], [ -1, %[[INNER_PREHEADER]] ]
+; CHECK-NEXT: br label %[[OUTER_HEADER_PREHEADER]]
+; CHECK: [[INNER_SPLIT1]]:
+; CHECK-NEXT: [[GEP:%.*]] = getelementptr [10 x i64], ptr [[A]], i64 [[I]], i64 [[J]]
+; CHECK-NEXT: store i64 [[K]], ptr [[GEP]], align 4
+; CHECK-NEXT: [[J_INC:%.*]] = add i64 [[J]], 1
+; CHECK-NEXT: [[EC_J:%.*]] = icmp eq i64 [[J_INC]], 10
+; CHECK-NEXT: br label %[[OUTER_LATCH]]
+; CHECK: [[INNER_SPLIT]]:
+; CHECK-NEXT: [[TMP0]] = add i64 [[J]], 1
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[TMP0]], 10
+; CHECK-NEXT: br i1 [[TMP1]], label %[[EXIT:.*]], label %[[INNER]]
+; CHECK: [[OUTER_LATCH]]:
+; CHECK-NEXT: [[I_INC]] = add i64 [[I]], 1
+; CHECK-NEXT: [[EC_I:%.*]] = icmp eq i64 [[I_INC]], 10
+; CHECK-NEXT: br i1 [[EC_I]], label %[[INNER_SPLIT]], label %[[OUTER_HEADER]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %outer.header
+
+outer.header:
+ %i = phi i64 [ 0, %entry ], [ %i.inc, %outer.latch ]
+ br label %inner
+
+inner:
+ %j = phi i64 [ 0, %outer.header ], [ %j.inc, %inner ]
+ %k = phi i64 [ -1, %outer.header ], [ %j, %inner ]
+ %gep = getelementptr [10 x i64], ptr %A, i64 %i, i64 %j
+ store i64 %k, ptr %gep
+ %j.inc = add i64 %j, 1
+ %ec.j = icmp eq i64 %j.inc, 10
+ br i1 %ec.j, label %outer.latch, label %inner
+
+outer.latch:
+ %i.inc = add i64 %i, 1
+ %ec.i = icmp eq i64 %i.inc, 10
+ br i1 %ec.i, label %exit, label %outer.header
+
+exit:
+ ret void
+}
>From 6f204532e65d9c3e374fcd7c5af583c72beaf43f Mon Sep 17 00:00:00 2001
From: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
Date: Tue, 28 Apr 2026 14:37:47 +0000
Subject: [PATCH 2/2] address review comments
---
llvm/lib/Transforms/Scalar/LoopInterchange.cpp | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index 1c249d5b9fb87..91e2510c33851 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -1946,9 +1946,9 @@ bool LoopInterchangeTransform::transform(
for (PHINode *CurInductionPHI : InductionPHIs) {
Instruction *IncomingValue = dyn_cast<Instruction>(
CurInductionPHI->getIncomingValueForBlock(InnerLoop->getLoopLatch()));
- if (any_of(InductionPHIs, [IncomingValue](PHINode *InductionPHI) {
- return IncomingValue == InductionPHI;
- }))
+ assert(IncomingValue &&
+ "Incoming value from loop latch doesn't an instruction");
+ if (is_contained(InductionPHIs, IncomingValue))
continue;
InnerIndexVarList.push_back(IncomingValue);
}
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