Don't do: "(X & 4) >> 1 == 2 --> (X & 4) == 4" if there are more than one uses of the shift result.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50118 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 32 insertions, 2 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 555942ddc1..c2019389ba 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -6065,13 +6065,14 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
     // Otherwise, check to see if the bits shifted out are known to be zero.
     // If so, we can compare against the unshifted value:
     //  (X & 4) >> 1 == 2  --> (X & 4) == 4.
-    if (MaskedValueIsZero(LHSI->getOperand(0), 
+    if (LHSI->hasOneUse() &&
+        MaskedValueIsZero(LHSI->getOperand(0), 
                           APInt::getLowBitsSet(Comp.getBitWidth(), ShAmtVal))) {
       return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0),
                           ConstantExpr::getShl(RHS, ShAmt));
     }
       
-    if (LHSI->hasOneUse() || RHSV == 0) {
+    if (LHSI->hasOneUse()) {
       // Otherwise strength reduce the shift into an and.
       APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
       Constant *Mask = ConstantInt::get(Val);
diff --git a/test/Transforms/InstCombine/shl-icmp.ll b/test/Transforms/InstCombine/shl-icmp.ll
new file mode 100644
index 0000000000..234c40bf68
--- /dev/null
+++ b/test/Transforms/InstCombine/shl-icmp.ll
@@ -0,0 +1,29 @@
+; RUN: llvm-as < %s | opt -instcombine -stats -disable-output |& \
+; RUN:   grep {Number of insts combined} | grep 5
+
+define i8 @t1(i8 zeroext %x, i8 zeroext %y) zeroext nounwind {
+entry:
+	%tmp1 = lshr i8 %x, 7
+	%cond1 = icmp ne i8 %tmp1, 0
+	br i1 %cond1, label %bb1, label %bb2
+
+bb1:
+	ret i8 %tmp1
+
+bb2:
+        %tmp2 = add i8 %tmp1, %y
+	ret i8 %tmp2
+}
+
+define i8 @t2(i8 zeroext %x) zeroext nounwind {
+entry:
+	%tmp1 = lshr i8 %x, 7
+	%cond1 = icmp ne i8 %tmp1, 0
+	br i1 %cond1, label %bb1, label %bb2
+
+bb1:
+	ret i8 0
+
+bb2:
+	ret i8 1
+}