[llvm] IR: introduce CmpInst::is{Eq,Ne}Equivalence (PR #111979)

[Matt Arsenault via llvm-commits]

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@@ -3471,6 +3471,63 @@ bool CmpInst::isEquality(Predicate P) {
   llvm_unreachable("Unsupported predicate kind");
 }
 
+// Returns true if either operand of CmpInst is a provably non-zero
+// floating-point constant. If both operands are constants, simply return the
+// equality of the constants.
+static bool hasNonZeroFPOperands(const CmpInst *Cmp) {
+  auto *LHS = dyn_cast<Constant>(Cmp->getOperand(0));
+  auto *RHS = dyn_cast<Constant>(Cmp->getOperand(1));
+  if (LHS && RHS)
+    return LHS == RHS;
+  if (auto *Const = LHS ? LHS : RHS) {
+    if (auto *ConstFP = dyn_cast<ConstantFP>(Const)) {
+      if (!ConstFP->isZero())
+        return true;
+    } else if (auto *ConstVec = dyn_cast<ConstantVector>(Const)) {
+      if (auto *SplatCFP =
+              dyn_cast_or_null<ConstantFP>(ConstVec->getSplatValue())) {
+        if (!SplatCFP->isZero())
+          return true;
+      }
+    }
+  }
+  return false;
+}
+
+// Floating-point equality is not an equivalence when comparing +0.0 with
+// -0.0 or when comparing NaN with another value.
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arsenm wrote:

Also need to consider DAZ with denormal values? 

https://github.com/llvm/llvm-project/pull/111979