[SelectionDAG] Correct the implementation of m_AllOnes. (llvm#90776)

Previously we used SpecificInt_match which created a 64 bit APInt
containing all ones. This was then checked against other constants by
using APInt::isSameValue.

If the constnats have different bitwidths, APInt::isSameValue will zero
extend the constant to make them match. This means for any constant less
than 64 bits, m_AllOnes was guaranteed to fail since the zero extended
value would not match all ones.

I think would also incorrectly consider an i128 with 64 leading zeros
and 64 trailing zeros as matching m_AllOnes.

To avoid this, this patch adds a new matcher class that just calls
isAllOnesOrAllOnesSplat.

Change-Id: I81e987f2a4f11650f7b3ac4624a586d9d39f167a

Author: topperc

llvm/include/llvm/CodeGen/SDPatternMatch.h

@@ -741,7 +741,17 @@ inline SpecificInt_match m_SpecificInt(uint64_t V) {
 
 inline SpecificInt_match m_Zero() { return m_SpecificInt(0U); }
 inline SpecificInt_match m_One() { return m_SpecificInt(1U); }
-inline SpecificInt_match m_AllOnes() { return m_SpecificInt(~0U); }
+
+struct AllOnes_match {
+
+  AllOnes_match() = default;
+
+  template <typename MatchContext> bool match(const MatchContext &, SDValue N) {
+    return isAllOnesOrAllOnesSplat(N);
+  }
+};
+
+inline AllOnes_match m_AllOnes() { return AllOnes_match(); }
 
 /// Match true boolean value based on the information provided by
 /// TargetLowering.
@@ -824,7 +834,7 @@ inline BinaryOpc_match<SpecificInt_match, ValTy> m_Neg(const ValTy &V) {
 
 /// Match a Not as a xor(v, -1) or xor(-1, v)
 template <typename ValTy>
-inline BinaryOpc_match<ValTy, SpecificInt_match, true> m_Not(const ValTy &V) {
+inline BinaryOpc_match<ValTy, AllOnes_match, true> m_Not(const ValTy &V) {
   return m_Xor(V, m_AllOnes());
 }