[llvm] r224553 - ConstantFold: Shifting undef by zero results in undef

[David Majnemer]

Author: majnemer
Date: Thu Dec 18 17:54:43 2014
New Revision: 224553

URL: http://llvm.org/viewvc/llvm-project?rev=224553&view=rev
Log:
ConstantFold: Shifting undef by zero results in undef

Modified:
    llvm/trunk/lib/IR/ConstantFold.cpp
    llvm/trunk/test/Transforms/InstSimplify/undef.ll

Modified: llvm/trunk/lib/IR/ConstantFold.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/ConstantFold.cpp?rev=224553&r1=224552&r2=224553&view=diff
==============================================================================
--- llvm/trunk/lib/IR/ConstantFold.cpp (original)
+++ llvm/trunk/lib/IR/ConstantFold.cpp Thu Dec 18 17:54:43 2014
@@ -956,12 +956,18 @@ Constant *llvm::ConstantFoldBinaryInstru
       // X >>l undef -> undef
       if (isa<UndefValue>(C2))
         return C2;
+      // undef >>l 0 -> undef
+      if (match(C2, m_Zero()))
+        return C1;
       // undef >>l X -> 0
       return Constant::getNullValue(C1->getType());
     case Instruction::AShr:
       // X >>a undef -> undef
       if (isa<UndefValue>(C2))
         return C2;
+      // undef >>a 0 -> undef
+      if (match(C2, m_Zero()))
+        return C1;
       // TODO: undef >>a X -> undef if the shift is exact
       // undef >>a X -> 0
       return Constant::getNullValue(C1->getType());
@@ -969,6 +975,9 @@ Constant *llvm::ConstantFoldBinaryInstru
       // X << undef -> undef
       if (isa<UndefValue>(C2))
         return C2;
+      // undef << 0 -> undef
+      if (match(C2, m_Zero()))
+        return C1;
       // undef << X -> 0
       return Constant::getNullValue(C1->getType());
     }

Modified: llvm/trunk/test/Transforms/InstSimplify/undef.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/undef.ll?rev=224553&r1=224552&r2=224553&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/undef.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/undef.ll Thu Dec 18 17:54:43 2014
@@ -244,3 +244,24 @@ define i32 @test31(i32 %a) {
   %b = shl i32 undef, %a
   ret i32 %b
 }
+
+; CHECK-LABEL: @test32
+; CHECK: ret i32 undef
+define i32 @test32(i32 %a) {
+  %b = shl i32 undef, 0
+  ret i32 %b
+}
+
+; CHECK-LABEL: @test33
+; CHECK: ret i32 undef
+define i32 @test33(i32 %a) {
+  %b = ashr i32 undef, 0
+  ret i32 %b
+}
+
+; CHECK-LABEL: @test34
+; CHECK: ret i32 undef
+define i32 @test34(i32 %a) {
+  %b = lshr i32 undef, 0
+  ret i32 %b
+}