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[InstCombine] Fix infinite loop due to bitcast <-> phi transforms #32

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Jan 16, 2020
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[InstCombine] Fix infinite loop due to bitcast <-> phi transforms #32

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11 changes: 8 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2234,9 +2234,14 @@ Instruction *InstCombiner::optimizeBitCastFromPhi(CastInst &CI, PHINode *PN) {
if (auto *C = dyn_cast<Constant>(V)) {
NewV = ConstantExpr::getBitCast(C, DestTy);
} else if (auto *LI = dyn_cast<LoadInst>(V)) {
Builder.SetInsertPoint(LI->getNextNode());
NewV = Builder.CreateBitCast(LI, DestTy);
Worklist.Add(LI);
// Explicitly perform load combine to make sure no opposing transform
// can remove the bitcast in the meantime and trigger an infinite loop.
Builder.SetInsertPoint(LI);
NewV = combineLoadToNewType(*LI, DestTy);
// Remove the old load and its use in the old phi, which itself becomes
// dead once the whole transform finishes.
replaceInstUsesWith(*LI, UndefValue::get(LI->getType()));
eraseInstFromFunction(*LI);
} else if (auto *BCI = dyn_cast<BitCastInst>(V)) {
NewV = BCI->getOperand(0);
} else if (auto *PrevPN = dyn_cast<PHINode>(V)) {
Expand Down
192 changes: 192 additions & 0 deletions llvm/test/Transforms/InstCombine/pr44245.ll
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@@ -0,0 +1,192 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -instcombine -instcombine-infinite-loop-threshold=2 < %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: [[TMP467:%.*]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
; CHECK-NEXT: br label [[BB47]]
; CHECK: bb47:
; CHECK-NEXT: [[TMP1]] = phi i8* [ [[TMP2:%.*]], [[BB150:%.*]] ], [ [[TMP1221:%.*]], [[BB119:%.*]] ], [ [[TMP1032:%.*]], [[BB101:%.*]] ], [ [[TMP933:%.*]], [[BB91:%.*]] ], [ [[TMP834:%.*]], [[BB81:%.*]] ], [ [[TMP705:%.*]], [[BB67:%.*]] ], [ [[TMP586:%.*]], [[BB56:%.*]] ], [ [[TMP467]], [[BB44]] ]
; CHECK-NEXT: br label [[BB17]]
; CHECK: bb49:
; CHECK-NEXT: br i1 [[C]], label [[BB56]], label [[BB59:%.*]]
; CHECK: bb56:
; CHECK-NEXT: [[TMP586]] = 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: [[TMP705]] = 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: [[TMP834]] = 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: [[TMP933]] = 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: [[TMP1032]] = 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: [[TMP1221]] = 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: [[TMP1499:%.*]] = load i8*, i8** inttoptr (i64 16 to i8**), align 16
; CHECK-NEXT: br label [[BB150]]
; CHECK: bb150:
; CHECK-NEXT: [[TMP2]] = phi i8* [ [[TMP1848:%.*]], [[BB152]] ], [ [[TMP1499]], [[BB147]] ]
; CHECK-NEXT: br label [[BB47]]
; CHECK: bb152:
; CHECK-NEXT: [[TMP1848]] = 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
}

; This used to cause an instcombine loop when the problem above was
; addressed in a non-robust fashion.

%type_1 = type {}
%type_2 = type {}
%type_3 = type {}

define void @test_2(i1 %c) local_unnamed_addr {
; CHECK-LABEL: @test_2(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[WHILE_COND:%.*]]
; CHECK: while.cond:
; CHECK-NEXT: br label [[FOR_COND:%.*]]
; CHECK: for.cond:
; CHECK-NEXT: br i1 [[C:%.*]], label [[COND_TRUE133:%.*]], label [[COND_FALSE138:%.*]]
; CHECK: cond.true133:
; CHECK-NEXT: store %type_3* undef, %type_3** null, align 536870912
; CHECK-NEXT: br label [[COND_END144:%.*]]
; CHECK: cond.false138:
; CHECK-NEXT: store %type_3* undef, %type_3** null, align 536870912
; CHECK-NEXT: br label [[COND_END144]]
; CHECK: cond.end144:
; CHECK-NEXT: br label [[WHILE_COND]]
;
entry:
br label %while.cond

while.cond: ; preds = %cond.end144, %entry
%link.0 = phi %type_2* [ undef, %entry ], [ %cond145, %cond.end144 ]
%os115 = bitcast %type_2* %link.0 to %type_3*
%ou116 = getelementptr inbounds %type_3, %type_3* %os115, i32 0
%os1117 = bitcast %type_3* %ou116 to %type_1*
br label %for.cond

for.cond: ; preds = %while.cond
br i1 %c, label %cond.true133, label %cond.false138

cond.true133: ; preds = %sw.epilog
%0 = load %type_2*, %type_2** undef, align 8
br label %cond.end144

cond.false138: ; preds = %sw.epilog
%1 = load %type_2*, %type_2** undef, align 8
br label %cond.end144

cond.end144: ; preds = %cond.false138, %cond.true133
%cond145 = phi %type_2* [ %0, %cond.true133 ], [ %1, %cond.false138 ]
br label %while.cond
}