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InstCombine: Check for zero shift amounts before subtracting one causing integer overflow.

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PR17026. Also avoid undefined shifts and shift amounts larger than 64 bits
(those are always undef because we can't represent integer types that large).

llvm-svn: 189672
This commit is contained in:
Benjamin Kramer 2013-08-30 14:35:35 +00:00
parent 163da340ac
commit 3a81691558
2 changed files with 51 additions and 10 deletions
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25
lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
View File

@ -845,21 +845,26 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
Value *InstCombiner::SimplifyShrShlDemandedBits(Instruction *Shr,
Instruction *Shl, APInt DemandedMask, APInt &KnownZero, APInt &KnownOne) {
unsigned ShlAmt = cast<ConstantInt>(Shl->getOperand(1))->getZExtValue();
unsigned ShrAmt = cast<ConstantInt>(Shr->getOperand(1))->getZExtValue();
const APInt &ShlOp1 = cast<ConstantInt>(Shl->getOperand(1))->getValue();
const APInt &ShrOp1 = cast<ConstantInt>(Shr->getOperand(1))->getValue();
if (!ShlOp1 || !ShrOp1)
return 0; // Noop.
Value *VarX = Shr->getOperand(0);
Type *Ty = VarX->getType();
unsigned BitWidth = Ty->getIntegerBitWidth();
if (ShlOp1.uge(BitWidth) || ShrOp1.uge(BitWidth))
return 0; // Undef.
unsigned ShlAmt = ShlOp1.getZExtValue();
unsigned ShrAmt = ShrOp1.getZExtValue();
KnownOne.clearAllBits();
KnownZero = APInt::getBitsSet(KnownZero.getBitWidth(), 0, ShlAmt-1);
KnownZero &= DemandedMask;
if (ShlAmt == 0 || ShrAmt == 0)
return 0;
Value *VarX = Shr->getOperand(0);
Type *Ty = VarX->getType();
APInt BitMask1(APInt::getAllOnesValue(Ty->getIntegerBitWidth()));
APInt BitMask2(APInt::getAllOnesValue(Ty->getIntegerBitWidth()));
APInt BitMask1(APInt::getAllOnesValue(BitWidth));
APInt BitMask2(APInt::getAllOnesValue(BitWidth));
bool isLshr = (Shr->getOpcode() == Instruction::LShr);
BitMask1 = isLshr ? (BitMask1.lshr(ShrAmt) << ShlAmt) :

36
test/Transforms/InstCombine/shift.ll
View File

@ -744,3 +744,39 @@ define i32 @test62(i32 %x) {
; CHECK-LABEL: @test62(
; CHECK: ashr exact i32 %x, 3
}
; PR17026
; CHECK-LABEL: @test63(
; CHECK-NOT: sh
; CHECK: ret
define void @test63(i128 %arg) {
bb:
br i1 undef, label %bb1, label %bb12
bb1: ; preds = %bb11, %bb
br label %bb2
bb2: ; preds = %bb7, %bb1
br i1 undef, label %bb3, label %bb7
bb3: ; preds = %bb2
%tmp = lshr i128 %arg, 36893488147419103232
%tmp4 = shl i128 %tmp, 0
%tmp5 = or i128 %tmp4, undef
%tmp6 = trunc i128 %tmp5 to i16
br label %bb8
bb7: ; preds = %bb2
br i1 undef, label %bb8, label %bb2
bb8: ; preds = %bb7, %bb3
%tmp9 = phi i16 [ %tmp6, %bb3 ], [ undef, %bb7 ]
%tmp10 = icmp eq i16 %tmp9, 0
br i1 %tmp10, label %bb11, label %bb12
bb11: ; preds = %bb8
br i1 undef, label %bb1, label %bb12
bb12: ; preds = %bb11, %bb8, %bb
ret void
}