[ConstantRange][SimplifyCFG] Add a helper method to allow SimplifyCFG to determine if a ConstantRange has more than 8 elements without requiring an allocation if the ConstantRange is 64-bits wide.

Previously SimplifyCFG used getSetSize which returns an APInt that is 1 bit wider than the ConstantRange's bit width. In the reasonably common case that the ConstantRange is 64-bits wide, this requires returning a 65-bit APInt. APInt's can only store 64-bits without a memory allocation so this is inefficient.

The new method takes the 8 as an input and tells if the range contains more than that many elements without requiring any wider math.

llvm-svn: 302385

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index cb703f6efc6..aeb1257754f 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -260,6 +260,17 @@ ConstantRange::isSizeStrictlySmallerThan(const ConstantRange &Other) const {
   return (Upper - Lower).ult(Other.Upper - Other.Lower);
 }
 
+bool
+ConstantRange::isSizeLargerThan(uint64_t MaxSize) const {
+  assert(MaxSize && "MaxSize can't be 0.");
+  // If this a full set, we need special handling to avoid needing an extra bit
+  // to represent the size.
+  if (isFullSet())
+    return APInt::getMaxValue(getBitWidth()).ugt(MaxSize - 1);
+
+  return (Upper - Lower).ugt(MaxSize);
+}
+
 APInt ConstantRange::getUnsignedMax() const {
   if (isFullSet() || isWrappedSet())
     return APInt::getMaxValue(getBitWidth());