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

[Matt Arsenault via llvm-branch-commits]

================
@@ -2086,6 +2091,131 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Value *V,
     Known.fneg();
     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;
+    }
+
+    const SimplifyQuery &SQ = getSimplifyQuery();
+    if (X == Y && isGuaranteedNotToBeUndef(X, SQ.AC, CxtI, SQ.DT, Depth + 1)) {
+
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arsenm wrote:

```suggestion
```

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