[llvm] [InstCombine] FP fold, cond ? x : -x == 0 into x == 0 #85250 (PR #85673)

[Jay Foad via llvm-commits]

================
@@ -7972,6 +7972,13 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
   Constant *RHSC;
   if (match(Op0, m_Instruction(LHSI)) && match(Op1, m_Constant(RHSC))) {
     switch (LHSI->getOpcode()) {
+    case Instruction::Select:
+      if (FCmpInst::isEquality(Pred) && match(RHSC, m_AnyZeroFP()) &&
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jayfoad wrote:

```suggestion
      // fcmp eq (cond ? x : -x), 0 --> fcmp eq x, 0
      if (FCmpInst::isEquality(Pred) && match(RHSC, m_AnyZeroFP()) &&
```

https://github.com/llvm/llvm-project/pull/85673