[llvm-branch-commits] [llvm] InstCombine: Handle fadd in SimplifyDemandedFPClass (PR #174853)

[Yingwei Zheng via llvm-branch-commits]

================
@@ -2091,6 +2110,86 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Value *V,
     Known.fneg();
     break;
   }
+  case Instruction::FAdd: {
+    KnownFPClass KnownLHS, KnownRHS;
+
+    const SimplifyQuery &SQ = getSimplifyQuery();
+
+    // fadd x, x can be handled more aggressively.
+    if (I->getOperand(0) == I->getOperand(1) &&
+        isGuaranteedNotToBeUndef(I->getOperand(0), SQ.AC, CxtI, SQ.DT,
+                                 Depth + 1)) {
+      FPClassTest SrcDemandedMask = DemandedMask;
+
+      // Doubling a subnormal could have resulted in a normal value.
+      if (DemandedMask & fcPosNormal)
+        SrcDemandedMask |= fcPosSubnormal;
+      if (DemandedMask & fcNegNormal)
+        SrcDemandedMask |= fcNegSubnormal;
+
+      // Doubling a normal could have resulted in an infinity.
+      if (DemandedMask & fcPosInf)
+        SrcDemandedMask |= fcPosNormal;
+      if (DemandedMask & fcNegInf)
+        SrcDemandedMask |= fcNegNormal;
+
+      if (SimplifyDemandedFPClass(I, 0, SrcDemandedMask, KnownLHS, Depth + 1))
+        return I;
+
+      Type *EltTy = VTy->getScalarType();
+      DenormalMode Mode = F.getDenormalMode(EltTy->getFltSemantics());
+      Known = KnownFPClass::fadd_self(KnownLHS, Mode);
+      KnownRHS = KnownLHS;
+    } else {
+      FPClassTest SrcDemandedMask = fcFinite;
+
+      // inf + (-inf) = nan
+      if (DemandedMask & fcNan)
+        SrcDemandedMask |= fcNan | fcInf;
+
+      if (DemandedMask & fcInf)
+        SrcDemandedMask |= fcInf;
+
+      if (SimplifyDemandedFPClass(I, 1, SrcDemandedMask, KnownRHS, Depth + 1) ||
+          SimplifyDemandedFPClass(I, 0, SrcDemandedMask, KnownLHS, Depth + 1))
+        return I;
+
+      Type *EltTy = VTy->getScalarType();
+      DenormalMode Mode = F.getDenormalMode(EltTy->getFltSemantics());
+      Known = KnownFPClass::fadd(KnownLHS, KnownRHS, Mode);
+    }
+
+    FPClassTest ValidResults = DemandedMask & Known.KnownFPClasses;
+    if (Constant *SingleVal =
+            getFPClassConstant(VTy, ValidResults, /*IsCanonicalizing=*/true))
+      return SingleVal;
+
+    // Propagate known result to simplify edge case checks.
+    bool ResultNotNan = (DemandedMask & fcNan) == fcNone;
+    if (ResultNotNan) {
+      KnownLHS.knownNot(fcNan);
+      KnownRHS.knownNot(fcNan);
+    }
+
+    // With nnan: X + {+/-}Inf --> {+/-}Inf
+    if (KnownRHS.isKnownAlways(fcInf | fcNan) &&
+        (ResultNotNan || KnownLHS.isKnownNever(fcNan)))
----------------
dtcxzyw wrote:

```suggestion
    KnownLHS.isKnownNever(fcNan))
```

https://github.com/llvm/llvm-project/pull/174853