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InstCombine: Fix infinite loop when encountering switch on trivial icmp.

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The test case feeds the following into InstCombine's visitSelect:
%tobool8 = icmp ne i32 0, 0
%phitmp = select i1 %tobool8, i32 3, i32 0
Then instcombine replaces the right side of the switch with 0, doesn't notice
that nothing changes and tries again indefinitely.

This fixes PR12897.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157587 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2012-05-28 19:18:16 +00:00
parent 21280e48c0
commit 37fa1c81ac
2 changed files with 40 additions and 1 deletions
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2
lib/Transforms/InstCombine/InstCombineSelect.cpp
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@ -498,7 +498,7 @@ Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
// NOTE: if we wanted to, this is where to detect integer MIN/MAX
if (isa<Constant>(CmpRHS)) {
if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
// Transform (X == C) ? X : Y -> (X == C) ? C : Y
SI.setOperand(1, CmpRHS);

39
test/Transforms/InstCombine/2012-05-28-select-hang.ll Normal file
View File

@ -0,0 +1,39 @@
; RUN: opt -S -instcombine < %s | FileCheck %s
@c = common global i8 0, align 1
@a = common global i8 0, align 1
@b = common global i8 0, align 1
define void @func() nounwind uwtable ssp {
entry:
%0 = load i8* @c, align 1
%conv = zext i8 %0 to i32
%or = or i32 %conv, 1
%conv1 = trunc i32 %or to i8
store i8 %conv1, i8* @a, align 1
%conv2 = zext i8 %conv1 to i32
%neg = xor i32 %conv2, -1
%and = and i32 1, %neg
%conv3 = trunc i32 %and to i8
store i8 %conv3, i8* @b, align 1
%1 = load i8* @a, align 1
%conv4 = zext i8 %1 to i32
%conv5 = zext i8 %conv3 to i32
%tobool = icmp ne i32 %conv4, 0
br i1 %tobool, label %land.rhs, label %land.end
land.rhs: ; preds = %entry
%tobool8 = icmp ne i32 %conv5, 0
br label %land.end
land.end: ; preds = %land.rhs, %entry
%2 = phi i1 [ false, %entry ], [ %tobool8, %land.rhs ]
%land.ext = zext i1 %2 to i32
%mul = mul nsw i32 3, %land.ext
%conv9 = trunc i32 %mul to i8
store i8 %conv9, i8* @a, align 1
ret void
; CHECK: @func
; CHECK-NOT: select
}