[llvm] [ValueTracking] Compute known FPClass from dominating condition (PR #80740)

[Yingwei Zheng via llvm-commits]

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@@ -4213,9 +4213,56 @@ llvm::fcmpImpliesClass(CmpInst::Predicate Pred, const Function &F, Value *LHS,
   return fcmpImpliesClass(Pred, F, LHS, *ConstRHS, LookThroughSrc);
 }
 
-static FPClassTest computeKnownFPClassFromAssumes(const Value *V,
-                                                  const SimplifyQuery &Q) {
-  FPClassTest KnownFromAssume = fcAllFlags;
+static KnownFPClass computeKnownFPClassFromContext(const Value *V,
+                                                   const SimplifyQuery &Q) {
+  KnownFPClass KnownFromContext;
+
+  if (!Q.CxtI)
+    return KnownFromContext;
+
+  if (Q.DC && Q.DT) {
+    auto computeKnownFPClassFromCmp = [&](CmpInst::Predicate Pred, Value *LHS,
+                                          Value *RHS) {
+      if (match(LHS, m_BitCast(m_Specific(V)))) {
+        Type *SrcType = V->getType();
+        Type *DstType = LHS->getType();
+
+        // Make sure the bitcast doesn't change between scalar and vector and
+        // doesn't change the number of vector elements.
+        if (SrcType->isVectorTy() == DstType->isVectorTy() &&
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dtcxzyw wrote:

I think it is time to introduce a matching helper to avoid duplicating the logic/tests :(


https://github.com/llvm/llvm-project/pull/80740