[pr19636] Fix known bit computation in urem instruction with power of two.

Patch by Andrey Kuharev.

llvm-svn: 209902

2 files changed, 19 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 51ae11dea21..65a3f0a94b1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2185,8 +2185,11 @@ void SelectionDAG::computeKnownBits(SDValue Op, APInt &KnownZero,
       const APInt &RA = Rem->getAPIntValue();
       if (RA.isPowerOf2()) {
         APInt LowBits = (RA - 1);
-        KnownZero |= ~LowBits;
-        computeKnownBits(Op.getOperand(0), KnownZero, KnownOne,Depth+1);
+        computeKnownBits(Op.getOperand(0), KnownZero2, KnownOne2, Depth + 1);
+
+        // The upper bits are all zero, the lower ones are unchanged.
+        KnownZero = KnownZero2 | ~LowBits;
+        KnownOne = KnownOne2 & LowBits;
         break;
       }
     }
diff --git a/llvm/test/CodeGen/X86/computeKnownBits_urem.ll b/llvm/test/CodeGen/X86/computeKnownBits_urem.ll
new file mode 100644
index 00000000000..9902e6f2597
--- /dev/null
+++ b/llvm/test/CodeGen/X86/computeKnownBits_urem.ll
@@ -0,0 +1,14 @@
+; RUN: llc -mtriple=x86_64-linux < %s | FileCheck %s
+define i32 @main() #0 {
+entry:
+  %a = alloca i32, align 4
+  store i32 1, i32* %a, align 4
+  %0 = load i32* %a, align 4
+  %or = or i32 1, %0
+  %and = and i32 1, %or
+  %rem = urem i32 %and, 1
+  %add = add i32 %rem, 1
+  ret i32 %add
+}
+; CHECK: $1, %eax
+; CHECK-NEXT: retq