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Fix an overly general check in SimplifyIndvar to handle useless phi cycles.

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The right way to check for a binary operation is
cast<BinaryOperator>. The original check: cast<Instruction> &&
numOperands() == 2 would match phi "instructions", leading to an
infinite loop in extreme corner case: a useless phi with operands
[self, constant] that prior optimization passes failed to remove,
being used in the loop by another useless phi, in turn being used by an
lshr or udiv.

Fixes PR11350: runaway iteration assertion.

llvm-svn: 144935
This commit is contained in:
Andrew Trick 2011-11-17 23:36:35 +00:00
parent 3b8d362511
commit 7dc21d8c0e
2 changed files with 31 additions and 2 deletions
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4
lib/Transforms/Utils/SimplifyIndVar.cpp
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@ -107,8 +107,8 @@ Value *SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand)
// Attempt to fold a binary operator with constant operand. // Attempt to fold a binary operator with constant operand.
// e.g. ((I + 1) >> 2) => I >> 2 // e.g. ((I + 1) >> 2) => I >> 2
if (IVOperand->getNumOperands() != 2 || if (!isa<BinaryOperator>(IVOperand)
!isa<ConstantInt>(IVOperand->getOperand(1))) || !isa<ConstantInt>(IVOperand->getOperand(1)))
return 0; return 0;
IVSrc = IVOperand->getOperand(0); IVSrc = IVOperand->getOperand(0);

29
test/Transforms/IndVarSimplify/2011-11-17-selfphi.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: opt < %s -indvars -S | FileCheck %s
; PR11350: Check that SimplifyIndvar handles a cycle of useless self-phis.
; CHECK: @test
; CHECK-NOT: lcssa = phi
define void @test() nounwind {
entry:
br label %for.cond.preheader
for.cond.preheader: ; preds = %entry
br label %for.cond.outer
for.cond.outer: ; preds = %for.cond.preheader, %for.end
%p_41.addr.0.ph = phi i32 [ %p_41.addr.1.lcssa, %for.end ], [ 1, %for.cond.preheader ]
br label %for.cond
for.cond:
br i1 true, label %for.end, label %for.ph
for.ph: ; preds = %for.cond4.preheader
br label %for.end
for.end:
%p_41.addr.1.lcssa = phi i32 [ undef, %for.ph ], [ %p_41.addr.0.ph, %for.cond ]
%p_68.lobit.i = lshr i32 %p_41.addr.1.lcssa, 31
%cmp7 = icmp eq i32 %p_41.addr.1.lcssa, 0
%conv8 = zext i1 %cmp7 to i32
br label %for.cond.outer
}