[IRBuilder] Add a helper function to intersect FMFs from two instructions

[dtcxzyw]

Address review comment in #121899 (comment)

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-llvm-ir

Author: Yingwei Zheng (dtcxzyw)

Changes

Address review comment in #121899 (comment)

---

Full diff: https://github.com/llvm/llvm-project/pull/122059.diff

3 Files Affected:

• (modified) llvm/include/llvm/IR/IRBuilder.h (+5)
• (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+5-7)
• (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+2-3)

diff --git a/llvm/include/llvm/IR/IRBuilder.h b/llvm/include/llvm/IR/IRBuilder.h
index b73309175f20d1..0332a6cc2e76ea 100644
--- a/llvm/include/llvm/IR/IRBuilder.h
+++ b/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.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 37a7c4d88b234d..051c00652fe337 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/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;
@@ -1431,8 +1430,7 @@ 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,
@@ -1469,7 +1467,7 @@ 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.
@@ -1486,8 +1484,8 @@ 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));
     }
   }
 
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 5494c70b34b1ef..c55c40c88bc845 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/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);
     }
 

[nikic]

LGTM

Btw, I'd probably make the Instruction* ctor of FMFSource explicit, so one has to write FMFSource(I). I found some of the method calls a bit confusing to read, esp the ones that don't have FMF in the name, as it's not really clear that the argument is used to get FMF and isn't just another value argument.

[dtcxzyw]

Btw, I'd probably make the Instruction* ctor of FMFSource explicit, so one has to write FMFSource(I).

The implicit ctor is designed to keep compatibility with downstream projects.