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[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
This commit is contained in:
Nikita Popov 2019-12-07 12:21:22 +01:00
parent f5b7dd3c9e
commit 27a0795943
2 changed files with 148 additions and 0 deletions
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6
llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -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;

142
llvm/test/Transforms/InstCombine/pr44245.ll Normal file
View File

@ -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
}