[ValueTracking, InstCombine] extend isKnownToBeAPowerOfTwo() to handle vector splat constants

We could try harder to handle non-splat vector constants too, 
but that seems much rarer to me.

Note that the div test isn't resolved because there's a check
for isIntegerTy() guarding that transform.

Differential Revision: http://reviews.llvm.org/D20497

llvm-svn: 270369

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 19fef59e1f3..38853478c06 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1500,9 +1500,10 @@ bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
   if (Constant *C = dyn_cast<Constant>(V)) {
     if (C->isNullValue())
       return OrZero;
-    if (ConstantInt *CI = dyn_cast<ConstantInt>(C))
-      return CI->getValue().isPowerOf2();
-    // TODO: Handle vector constants.
+
+    const APInt *ConstIntOrConstSplatInt;
+    if (match(C, m_APInt(ConstIntOrConstSplatInt)))
+      return ConstIntOrConstSplatInt->isPowerOf2();
   }
 
   // 1 << X is clearly a power of two if the one is not shifted off the end.  If