[llvm] r189672 - InstCombine: Check for zero shift amounts before subtracting one causing integer overflow.
Benjamin Kramer
benny.kra at googlemail.com
Fri Aug 30 07:35:35 PDT 2013
Author: d0k
Date: Fri Aug 30 09:35:35 2013
New Revision: 189672
URL: http://llvm.org/viewvc/llvm-project?rev=189672&view=rev
Log:
InstCombine: Check for zero shift amounts before subtracting one causing integer overflow.
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).
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
llvm/trunk/test/Transforms/InstCombine/shift.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp?rev=189672&r1=189671&r2=189672&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp Fri Aug 30 09:35:35 2013
@@ -845,21 +845,26 @@ Value *InstCombiner::SimplifyDemandedUse
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) :
Modified: llvm/trunk/test/Transforms/InstCombine/shift.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/shift.ll?rev=189672&r1=189671&r2=189672&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/shift.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/shift.ll Fri Aug 30 09:35:35 2013
@@ -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
+}
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