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

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).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189672 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index a7bfe0965b03c5a50f9e3d8f9b9856a324a37158..a2492d87c0152a7ccabe8d213120f5297de494b2 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -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) :

diff --git a/test/Transforms/InstCombine/shift.ll b/test/Transforms/InstCombine/shift.ll
index 0bdab139b7c90950c0e364eca7c56b1672c58c0f..b1082f06ef7493136ac8c75f5989f3b5966f5d44 100644 (file)
--- a/test/Transforms/InstCombine/shift.ll
+++ b/test/Transforms/InstCombine/shift.ll
@@ -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
+}