[llvm-branch-commits] [llvm] InstCombine: Handle fmul in SimplifyDemandedFPClass (PR #173872)

[Matt Arsenault via llvm-branch-commits]

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@@ -2280,6 +2290,127 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Value *V,
     Known = KnownLHS | KnownRHS;
     break;
   }
+  case Instruction::FMul: {
+    KnownFPClass KnownLHS, KnownRHS;
+
+    Value *X = I->getOperand(0);
+    Value *Y = I->getOperand(1);
+
+    FPClassTest SrcDemandedMask =
+        DemandedMask & (fcNan | fcZero | fcSubnormal | fcNormal);
+
+    if (DemandedMask & fcInf) {
+      // mul x, inf = inf
+      // mul large_x, large_y = inf
+      SrcDemandedMask |= fcSubnormal | fcNormal | fcInf;
+    }
+
+    if (DemandedMask & fcNan) {
+      // mul +/-inf, 0 => nan
+      SrcDemandedMask |= fcZero | fcInf;
+
+      // TODO: Mode check
+      // mul +/-inf, sub => nan if daz
+      SrcDemandedMask |= fcSubnormal;
+    }
+
+    if (X == Y) {
+      if (SimplifyDemandedFPClass(I, 0, SrcDemandedMask, KnownLHS, Depth + 1))
+        return I;
+      Type *EltTy = VTy->getScalarType();
+
+      DenormalMode Mode = F.getDenormalMode(EltTy->getFltSemantics());
+      Known = KnownFPClass::square(KnownLHS, Mode);
+
+      // Propagate known result to simplify edge case checks.
+      if ((DemandedMask & fcNan) == fcNone)
+        Known.knownNot(fcNan);
+      if ((DemandedMask & fcPosInf) == fcNone)
+        Known.knownNot(fcInf);
+
+      FPClassTest ValidResults = DemandedMask & Known.KnownFPClasses;
+      if (Constant *Folded =
+              getFPClassConstant(VTy, ValidResults, /*IsCanonicalizing=*/true))
+        return Folded;
+
+      if (Known.isKnownAlways(fcPosZero | fcPosInf | fcNan)) {
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arsenm wrote:

This is checking the result, which should assume inf is a possible result for normal inputs, so everything here seems to work as intended. I'll add an assert that the source isn't normal 

https://github.com/llvm/llvm-project/pull/173872