[IRBuilder] Add a helper function to intersect FMFs from two instructions (#122059)

Address review comment in
llvm/llvm-project#121899 (comment)

Author: dtcxzyw

llvm/include/llvm/IR/IRBuilder.h

@@ -102,6 +102,11 @@ class FMFSource {
   FastMathFlags get(FastMathFlags Default) const {
     return FMF.value_or(Default);
   }
+  /// Intersect the FMF from two instructions.
+  static FMFSource intersect(Value *A, Value *B) {
+    return FMFSource(cast<FPMathOperator>(A)->getFastMathFlags() &
+                     cast<FPMathOperator>(B)->getFastMathFlags());
+  }
 };
 
 /// Common base class shared among various IRBuilders.

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -39,8 +39,7 @@ static Value *getNewICmpValue(unsigned Code, bool Sign, Value *LHS, Value *RHS,
 /// This is the complement of getFCmpCode, which turns an opcode and two
 /// operands into either a FCmp instruction, or a true/false constant.
 static Value *getFCmpValue(unsigned Code, Value *LHS, Value *RHS,
-                           InstCombiner::BuilderTy &Builder,
-                           FastMathFlags FMF) {
+                           InstCombiner::BuilderTy &Builder, FMFSource FMF) {
   FCmpInst::Predicate NewPred;
   if (Constant *TorF = getPredForFCmpCode(Code, LHS->getType(), NewPred))
     return TorF;
@@ -1406,8 +1405,7 @@ static Value *matchIsFiniteTest(InstCombiner::BuilderTy &Builder, FCmpInst *LHS,
     return nullptr;
 
   return Builder.CreateFCmpFMF(FCmpInst::getOrderedPredicate(PredR), RHS0, RHS1,
-                               LHS->getFastMathFlags() &
-                                   RHS->getFastMathFlags());
+                               FMFSource::intersect(LHS, RHS));
 }
 
 Value *InstCombinerImpl::foldLogicOfFCmps(FCmpInst *LHS, FCmpInst *RHS,
@@ -1444,7 +1442,7 @@ Value *InstCombinerImpl::foldLogicOfFCmps(FCmpInst *LHS, FCmpInst *RHS,
     // Intersect the fast math flags.
     // TODO: We can union the fast math flags unless this is a logical select.
     return getFCmpValue(NewPred, LHS0, LHS1, Builder,
-                        LHS->getFastMathFlags() & RHS->getFastMathFlags());
+                        FMFSource::intersect(LHS, RHS));
   }
 
   // This transform is not valid for a logical select.
@@ -1461,8 +1459,8 @@ Value *InstCombinerImpl::foldLogicOfFCmps(FCmpInst *LHS, FCmpInst *RHS,
       // Ignore the constants because they are obviously not NANs:
       // (fcmp ord x, 0.0) & (fcmp ord y, 0.0)  -> (fcmp ord x, y)
       // (fcmp uno x, 0.0) | (fcmp uno y, 0.0)  -> (fcmp uno x, y)
-      return Builder.CreateFCmpFMF(
-          PredL, LHS0, RHS0, LHS->getFastMathFlags() & RHS->getFastMathFlags());
+      return Builder.CreateFCmpFMF(PredL, LHS0, RHS0,
+                                   FMFSource::intersect(LHS, RHS));
     }
   }
 

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -2674,9 +2674,8 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     // copysign Mag, (copysign ?, X) --> copysign Mag, X
     Value *X;
     if (match(Sign, m_Intrinsic<Intrinsic::copysign>(m_Value(), m_Value(X)))) {
-      Value *CopySign = Builder.CreateCopySign(
-          Mag, X,
-          II->getFastMathFlags() & cast<Instruction>(Sign)->getFastMathFlags());
+      Value *CopySign =
+          Builder.CreateCopySign(Mag, X, FMFSource::intersect(II, Sign));
       return replaceInstUsesWith(*II, CopySign);
     }