[PATCH] D28986: [APInt] Remove calls to clearUnusedBits from XorSlowCase and operator^=

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.

There's a comment in XorSlowCase that says "0^0==1" which isn't true. 0 xored with 0 is still 0. So I don't think we need to clear any unused bits here.

Now there is no difference between XorSlowCase and AndSlowCase/OrSlowCase other than the operation being performed


https://reviews.llvm.org/D28986

Files:
  lib/Support/APInt.cpp


Index: lib/Support/APInt.cpp
===================================================================
--- lib/Support/APInt.cpp
+++ lib/Support/APInt.cpp
@@ -440,13 +440,12 @@
   assert(BitWidth == RHS.BitWidth && "Bit widths must be the same");
   if (isSingleWord()) {
     VAL ^= RHS.VAL;
-    this->clearUnusedBits();
     return *this;
   }
   unsigned numWords = getNumWords();
   for (unsigned i = 0; i < numWords; ++i)
     pVal[i] ^= RHS.pVal[i];
-  return clearUnusedBits();
+  return *this;
 }
 
 APInt APInt::AndSlowCase(const APInt& RHS) const {
@@ -470,11 +469,7 @@
   uint64_t *val = getMemory(numWords);
   for (unsigned i = 0; i < numWords; ++i)
     val[i] = pVal[i] ^ RHS.pVal[i];
-
-  APInt Result(val, getBitWidth());
-  // 0^0==1 so clear the high bits in case they got set.
-  Result.clearUnusedBits();
-  return Result;
+  return APInt(val, getBitWidth());
 }
 
 APInt APInt::operator*(const APInt& RHS) const {


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