Reland r216439 215441, majnemer has a real fix for PR20771.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216586 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/PatternMatch.h

@@ -362,6 +362,29 @@ struct bind_const_intval_ty {
   }
 };
 
+/// Match a specified integer value or vector of all elements of that value.
+struct specific_intval {
+  uint64_t Val;
+  specific_intval(uint64_t V) : Val(V) {}
+
+  template<typename ITy>
+  bool match(ITy *V) {
+    ConstantInt *CI = dyn_cast<ConstantInt>(V);
+    if (!CI && V->getType()->isVectorTy())
+      if (const auto *C = dyn_cast<Constant>(V))
+        CI = dyn_cast_or_null<ConstantInt>(C->getSplatValue());
+
+    if (CI && CI->getBitWidth() <= 64)
+      return CI->getZExtValue() == Val;
+
+    return false;
+  }
+};
+
+/// Match a specific integer value or vector with all elements equal to the
+/// value.
+inline specific_intval m_SpecificInt(uint64_t V) { return specific_intval(V); }
+
 /// m_ConstantInt - Match a ConstantInt and bind to its value.  This does not
 /// match ConstantInts wider than 64-bits.
 inline bind_const_intval_ty m_ConstantInt(uint64_t &V) { return V; }