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Fix PR2697 by rewriting the '(X / pos) op neg' logic. This also changes

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a couple other cases for clarity, but shouldn't affect correctness.

Patch by Eli Friedman!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57387 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-10-11 22:55:00 +00:00
parent 1b8f4bb4a1
commit a6321b40c2
2 changed files with 23 additions and 10 deletions
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25
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -5784,6 +5784,11 @@ Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
return 0;
if (DivRHS->isZero())
return 0; // The ProdOV computation fails on divide by zero.
if (DivIsSigned && DivRHS->isAllOnesValue())
return 0; // The overflow computation also screws up here
if (DivRHS->isOne())
return 0; // Not worth bothering, and eliminates some funny cases
// with INT_MIN.
// Compute Prod = CI * DivRHS. We are essentially solving an equation
// of form X/C1=C2. We solve for X by multiplying C1 (DivRHS) and
@ -5810,7 +5815,6 @@ Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
int LoOverflow = 0, HiOverflow = 0;
ConstantInt *LoBound = 0, *HiBound = 0;
if (!DivIsSigned) { // udiv
// e.g. X/5 op 3 --> [15, 20)
LoBound = Prod;
@ -5829,11 +5833,13 @@ Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
HiOverflow = AddWithOverflow(HiBound, Prod, DivRHS, true);
} else { // (X / pos) op neg
// e.g. X/5 op -3 --> [-15-4, -15+1) --> [-19, -14)
Constant *DivRHSH = ConstantExpr::getNeg(SubOne(DivRHS));
LoOverflow = AddWithOverflow(LoBound, Prod,
cast<ConstantInt>(DivRHSH), true) ? -1 : 0;
HiBound = AddOne(Prod);
HiOverflow = ProdOV ? -1 : 0;
LoOverflow = HiOverflow = ProdOV ? -1 : 0;
if (!LoOverflow) {
ConstantInt* DivNeg = cast<ConstantInt>(ConstantExpr::getNeg(DivRHS));
LoOverflow = AddWithOverflow(LoBound, HiBound, DivNeg,
true) ? -1 : 0;
}
}
} else if (DivRHS->getValue().isNegative()) { // Divisor is < 0.
if (CmpRHSV == 0) { // (X / neg) op 0
@ -5846,14 +5852,13 @@ Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
}
} else if (CmpRHSV.isStrictlyPositive()) { // (X / neg) op pos
// e.g. X/-5 op 3 --> [-19, -14)
HiBound = AddOne(Prod);
HiOverflow = LoOverflow = ProdOV ? -1 : 0;
if (!LoOverflow)
LoOverflow = AddWithOverflow(LoBound, Prod, AddOne(DivRHS), true) ?-1:0;
HiBound = AddOne(Prod);
LoOverflow = AddWithOverflow(LoBound, HiBound, DivRHS, true) ? -1 : 0;
} else { // (X / neg) op neg
// e.g. X/-5 op -3 --> [15, 20)
LoBound = Prod;
LoOverflow = HiOverflow = ProdOV ? 1 : 0;
LoBound = Prod; // e.g. X/-5 op -3 --> [15, 20)
LoOverflow = HiOverflow = ProdOV;
if (!HiOverflow)
HiOverflow = SubWithOverflow(HiBound, Prod, DivRHS, true);
}

8
test/Transforms/InstCombine/2008-10-11-DivCompareFold.ll Normal file
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@ -0,0 +1,8 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {ret i1 false}
; PR2697
define i1 @x(i32 %x) nounwind {
%div = sdiv i32 %x, 65536 ; <i32> [#uses=1]
%cmp = icmp slt i32 %div, -65536
ret i1 %cmp
}