[llvm] 27a0795 - [InstCombine] Fix infinite loop due to bitcast <-> phi transforms
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Tue Dec 31 07:17:53 PST 2019
Author: Nikita Popov
Date: 2019-12-31T16:17:14+01:00
New Revision: 27a0795943fee0f30b995fe5165428afc2dfd402
URL: https://github.com/llvm/llvm-project/commit/27a0795943fee0f30b995fe5165428afc2dfd402
DIFF: https://github.com/llvm/llvm-project/commit/27a0795943fee0f30b995fe5165428afc2dfd402.diff
LOG: [InstCombine] Fix infinite loop due to bitcast <-> phi transforms
Fix for https://bugs.llvm.org/show_bug.cgi?id=44245.
The optimizeBitCastFromPhi() and FoldPHIArgOpIntoPHI() end up
fighting against each other, because optimizeBitCastFromPhi()
assumes that bitcasts of loads will get folded. This doesn't happen
here, because a dangling phi node prevents the one-use fold in
https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp#L620-L628 from triggering.
This patch fixes the issue by adding manually removing the old phis.
Differential Revision: https://reviews.llvm.org/D71164
Added:
llvm/test/Transforms/InstCombine/pr44245.ll
Modified:
llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 3ba56bbe53e0..446e67580962 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -2370,6 +2370,12 @@ Instruction *InstCombiner::optimizeBitCastFromPhi(CastInst &CI, PHINode *PN) {
llvm_unreachable("all uses should be handled");
}
}
+
+ // At this point the old phi has either no users, or is only used
+ // in other old phis. Replace with undef to break circles and remove
+ // the instruction.
+ replaceInstUsesWith(*OldPN, UndefValue::get(OldPN->getType()));
+ eraseInstFromFunction(*OldPN);
}
return RetVal;
diff --git a/llvm/test/Transforms/InstCombine/pr44245.ll b/llvm/test/Transforms/InstCombine/pr44245.ll
new file mode 100644
index 000000000000..3b9e252187dc
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pr44245.ll
@@ -0,0 +1,142 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+; This used to cause on infinite instcombine loop.
+
+define void @test(i1 %c) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT: bb16:
+; CHECK-NEXT: br i1 [[C:%.*]], label [[BB17:%.*]], label [[BB24:%.*]]
+; CHECK: bb17:
+; CHECK-NEXT: [[TMP0:%.*]] = phi i8* [ [[TMP1:%.*]], [[BB47:%.*]] ], [ undef, [[BB16:%.*]] ]
+; CHECK-NEXT: store i8* [[TMP0]], i8** undef, align 8
+; CHECK-NEXT: ret void
+; CHECK: bb24:
+; CHECK-NEXT: br i1 [[C]], label [[BB44:%.*]], label [[BB49:%.*]]
+; CHECK: bb44:
+; CHECK-NEXT: [[TMP469:%.*]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: br label [[BB47]]
+; CHECK: bb47:
+; CHECK-NEXT: [[TMP1]] = phi i8* [ [[TMP2:%.*]], [[BB150:%.*]] ], [ [[TMP1223:%.*]], [[BB119:%.*]] ], [ [[TMP1034:%.*]], [[BB101:%.*]] ], [ [[TMP935:%.*]], [[BB91:%.*]] ], [ [[TMP836:%.*]], [[BB81:%.*]] ], [ [[TMP707:%.*]], [[BB67:%.*]] ], [ [[TMP588:%.*]], [[BB56:%.*]] ], [ [[TMP469]], [[BB44]] ]
+; CHECK-NEXT: br label [[BB17]]
+; CHECK: bb49:
+; CHECK-NEXT: br i1 [[C]], label [[BB56]], label [[BB59:%.*]]
+; CHECK: bb56:
+; CHECK-NEXT: [[TMP588]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: br label [[BB47]]
+; CHECK: bb59:
+; CHECK-NEXT: br i1 [[C]], label [[BB67]], label [[BB71:%.*]]
+; CHECK: bb67:
+; CHECK-NEXT: [[TMP707]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: br label [[BB47]]
+; CHECK: bb71:
+; CHECK-NEXT: br i1 [[C]], label [[BB81]], label [[BB84:%.*]]
+; CHECK: bb81:
+; CHECK-NEXT: [[TMP836]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: br label [[BB47]]
+; CHECK: bb84:
+; CHECK-NEXT: br i1 [[C]], label [[BB91]], label [[BB94:%.*]]
+; CHECK: bb91:
+; CHECK-NEXT: [[TMP935]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: br label [[BB47]]
+; CHECK: bb94:
+; CHECK-NEXT: br i1 [[C]], label [[BB101]], label [[BB104:%.*]]
+; CHECK: bb101:
+; CHECK-NEXT: [[TMP1034]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: br label [[BB47]]
+; CHECK: bb104:
+; CHECK-NEXT: br i1 [[C]], label [[BB119]], label [[BB123:%.*]]
+; CHECK: bb119:
+; CHECK-NEXT: [[TMP1223]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: br label [[BB47]]
+; CHECK: bb123:
+; CHECK-NEXT: br i1 [[C]], label [[BB147:%.*]], label [[BB152:%.*]]
+; CHECK: bb147:
+; CHECK-NEXT: [[TMP1492:%.*]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: br label [[BB150]]
+; CHECK: bb150:
+; CHECK-NEXT: [[TMP2]] = phi i8* [ [[TMP1841:%.*]], [[BB152]] ], [ [[TMP1492]], [[BB147]] ]
+; CHECK-NEXT: br label [[BB47]]
+; CHECK: bb152:
+; CHECK-NEXT: [[TMP1841]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
+; CHECK-NEXT: call void undef()
+; CHECK-NEXT: br label [[BB150]]
+;
+bb16: ; preds = %bb
+ br i1 %c, label %bb17, label %bb24
+
+bb17: ; preds = %bb47, %bb17
+ %0 = phi i8* [ %1, %bb47 ], [ undef, %bb16 ]
+ store i8* %0, i8** undef, align 8
+ ret void
+
+bb24: ; preds = %bb24
+ br i1 %c, label %bb44, label %bb49
+
+bb44: ; preds = %bb43
+ %tmp46 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ br label %bb47
+
+bb47: ; preds = %bb150, %bb119, %bb101, %bb91, %bb81, %bb67, %bb56, %bb44
+ %.in1 = phi i64* [ %.in, %bb150 ], [ %tmp122, %bb119 ], [ %tmp103, %bb101 ], [ %tmp93, %bb91 ], [ %tmp83, %bb81 ], [ %tmp70, %bb67 ], [ %tmp58, %bb56 ], [ %tmp46, %bb44 ]
+ %1 = bitcast i64* %.in1 to i8*
+ br label %bb17
+
+bb49: ; preds = %bb49
+ br i1 %c, label %bb56, label %bb59
+
+bb56: ; preds = %bb55
+ %tmp58 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ br label %bb47
+
+bb59: ; preds = %bb59
+ br i1 %c, label %bb67, label %bb71
+
+bb67: ; preds = %bb66
+ %tmp70 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ br label %bb47
+
+bb71: ; preds = %bb71
+ br i1 %c, label %bb81, label %bb84
+
+bb81: ; preds = %bb80
+ %tmp83 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ br label %bb47
+
+bb84: ; preds = %bb84
+ br i1 %c, label %bb91, label %bb94
+
+bb91: ; preds = %bb90
+ %tmp93 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ br label %bb47
+
+bb94: ; preds = %bb94
+ br i1 %c, label %bb101, label %bb104
+
+bb101: ; preds = %bb100
+ %tmp103 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ br label %bb47
+
+bb104: ; preds = %bb104
+ br i1 %c, label %bb119, label %bb123
+
+bb119: ; preds = %bb118
+ %tmp122 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ br label %bb47
+
+bb123: ; preds = %bb123
+ br i1 %c, label %bb147, label %bb152
+
+bb147: ; preds = %bb146
+ %tmp149 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ br label %bb150
+
+bb150: ; preds = %bb152, %bb147
+ %.in = phi i64* [ %tmp184, %bb152 ], [ %tmp149, %bb147 ]
+ br label %bb47
+
+bb152: ; preds = %bb146
+ %tmp184 = load i64*, i64** inttoptr (i64 16 to i64**), align 16
+ call void undef()
+ br label %bb150
+}
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