make ConstantRange::zeroExtend() optimal
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160643 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/ConstantRange.cpp b/lib/Support/ConstantRange.cpp
index a3f2297..720ef36 100644
--- a/lib/Support/ConstantRange.cpp
+++ b/lib/Support/ConstantRange.cpp
@@ -427,9 +427,13 @@
unsigned SrcTySize = getBitWidth();
assert(SrcTySize < DstTySize && "Not a value extension");
- if (isFullSet() || isWrappedSet())
+ if (isFullSet() || isWrappedSet()) {
// Change into [0, 1 << src bit width)
- return ConstantRange(APInt(DstTySize,0), APInt(DstTySize,1).shl(SrcTySize));
+ APInt LowerExt(DstTySize, 0);
+ if (!Upper) // special case: [X, 0) -- not really wrapping around
+ LowerExt = Lower.zext(DstTySize);
+ return ConstantRange(LowerExt, APInt(DstTySize, 1).shl(SrcTySize));
+ }
return ConstantRange(Lower.zext(DstTySize), Upper.zext(DstTySize));
}