ValueTracking: Handle no-nan check for computeKnownFPClass for fmul

[arsenm]

Summary

Copy the logic from isKnownNeverNaN for fadd/fsub. Leave the
extension to handle the zero case for a future change (which also doesn't sound right to me)

[arsenm]

Rebase on baseline attributor test which is easier than unit tests

[nikic]

LGTM

[arsenm]

4d044bfb33980a3453c9cd456c261750f1971b8a

llvm/lib/Analysis/ValueTracking.cpp

if (KnownRHS.isKnownNeverNaN()) {
       // Adding positive and negative infinity produces NaN.
       if (KnownLHS.isKnownNeverNaN() &&
           (KnownLHS.isKnownNeverInfinity() || KnownRHS.isKnownNeverInfinity()))
         Known.knownNot(fcNan);
     }
 
     break;
   }
+  case Instruction::FMul: {
+    KnownFPClass KnownLHS, KnownRHS;
+    computeKnownFPClass(Op->getOperand(1), DemandedElts, fcNan | fcInf,
+                        KnownRHS, Depth + 1, Q, TLI);
+    if (KnownRHS.isKnownNeverNaN() && KnownRHS.isKnownNeverInfinity()) {
+      computeKnownFPClass(Op->getOperand(0), DemandedElts, fcNan | fcInf,
+                          KnownLHS, Depth + 1, Q, TLI);
+
+      // Zero multiplied with infinity produces NaN.
+      // FIXME: If neither side can be zero fmul never produces NaN.
+      if (KnownLHS.isKnownNeverNaN() && KnownLHS.isKnownNeverInfinity())
+        Known.knownNot(fcNan);
+    }
+
+    break;
+  }
   case Instruction::SIToFP:
   case Instruction::UIToFP: {
     // Cannot produce nan
     Known.knownNot(fcNan);
     if (Op->getOpcode() == Instruction::UIToFP)
       Known.signBitIsZero();
 
     if (InterestedClasses & fcInf) {

llvm/unittests/Analysis/ValueTrackingTest.cpp

parseAssembly(
       "}\n");
   expectKnownFPClass(fcFinite | fcInf, std::nullopt, A);
   expectKnownFPClass(fcFinite | fcInf, std::nullopt, A2);
   expectKnownFPClass(fcAllFlags, std::nullopt, A3);
   expectKnownFPClass(fcAllFlags, std::nullopt, A4);
   expectKnownFPClass(fcAllFlags, std::nullopt, A5);
 }
 
+TEST_F(ComputeKnownFPClassTest, FMul) {
+  parseAssembly(
+      "define float @test(float nofpclass(nan inf) %nnan.ninf, float nofpclass(nan) %nnan, float nofpclass(qnan) %no.qnan, float %unknown) {\n"
+      "  %A = fmul float %nnan.ninf, %nnan.ninf"
+      "  %A2 = fmul float %nnan.ninf, %nnan"
+      "  %A3 = fmul float %nnan, %nnan.ninf"
+      "  %A4 = fmul float %nnan.ninf, %no.qnan"
+      "  %A5 = fmul float %nnan, %nnan"
+      "  ret float %A\n"
+      "}\n");
+  expectKnownFPClass(fcFinite | fcInf, std::nullopt, A);
+  expectKnownFPClass(fcAllFlags, std::nullopt, A2);
+  expectKnownFPClass(fcAllFlags, std::nullopt, A3);
+  expectKnownFPClass(fcAllFlags, std::nullopt, A4);
+  expectKnownFPClass(fcAllFlags, std::nullopt, A5);
+}
+
 TEST_F(ValueTrackingTest, isNonZeroRecurrence) {
   parseAssembly(R"(
     define i1 @test(i8 %n, i8 %r) {
     entry:
       br label %loop
     loop:
       %p = phi i8 [ -1, %entry ], [ %next, %loop ]
       %next = add nsw i8 %p, -1