Fix a miscompilation from Dan's recent apintification.

llvm-svn: 47128

2 files changed, 9 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 76cf425499e..f8e1fea679c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1437,12 +1437,10 @@ void SelectionDAG::ComputeMaskedBits(SDOperand Op, const APInt &Mask,
     // We know that the top bits of C-X are clear if X contains less bits
     // than C (i.e. no wrap-around can happen).  For example, 20-X is
     // positive if we can prove that X is >= 0 and < 16.
-
-    // sign bit clear
     if (CLHS->getAPIntValue().isNonNegative()) {
       unsigned NLZ = (CLHS->getAPIntValue()+1).countLeadingZeros();
       // NLZ can't be BitWidth with no sign bit
-      APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ);
+      APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
       ComputeMaskedBits(Op.getOperand(1), MaskV, KnownZero, KnownOne, Depth+1);
 
       // If all of the MaskV bits are known to be zero, then we know the output
diff --git a/llvm/test/CodeGen/X86/2008-02-14-BitMiscompile.ll b/llvm/test/CodeGen/X86/2008-02-14-BitMiscompile.ll
new file mode 100644
index 00000000000..5bf84560a37
--- /dev/null
+++ b/llvm/test/CodeGen/X86/2008-02-14-BitMiscompile.ll
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | llc -march=x86 | grep and
+define i32 @test(i1 %A) {
+	%B = zext i1 %A to i32		; <i32> [#uses=1]
+	%C = sub i32 0, %B		; <i32> [#uses=1]
+	%D = and i32 %C, 255		; <i32> [#uses=1]
+	ret i32 %D
+}
+