[llvm] [GlobalIsel] Canonicalize G_FCMP (PR #108891)

[Thorsten Schütt via llvm-commits]

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@@ -84,3 +115,31 @@ bool CombinerHelper::matchCanonicalizeICmp(const MachineInstr &MI,
 
   return false;
 }
+
+bool CombinerHelper::matchCanonicalizeFCmp(const MachineInstr &MI,
+                                           BuildFnTy &MatchInfo) {
+  const GFCmp *Cmp = cast<GFCmp>(&MI);
+
+  Register Dst = Cmp->getReg(0);
+  Register LHS = Cmp->getLHSReg();
+  Register RHS = Cmp->getRHSReg();
+
+  CmpInst::Predicate Pred = Cmp->getCond();
+  assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
+
+  if (auto CLHS = GFConstant::getConstant(LHS, MRI)) {
+    if (auto CRHS = GFConstant::getConstant(RHS, MRI))
+      return constantFoldFCmp(*Cmp, *CLHS, *CRHS, MatchInfo);
+
+    // If we have a constant, make sure it is on the RHS.
+    std::swap(LHS, RHS);
+    Pred = CmpInst::getSwappedPredicate(Pred);
+
+    MatchInfo = [=](MachineIRBuilder &B) {
+      B.buildFCmp(Pred, Dst, LHS, RHS, Cmp->getFlags());
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tschuett wrote:

confidential

https://github.com/llvm/llvm-project/pull/108891