[PATCH] D148187: [GISel] Legalize G_FSUB to G_FADD + G_FNEG even if G_FNEG is illegal

Sergei Barannikov via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Wed Apr 12 18:42:56 PDT 2023

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`G_FNEG` used to be legalized to `G_FSUB -0, x` causing infinite loop.
This is no longer the case after D84287 <https://reviews.llvm.org/D84287>.

  rG LLVM Github Monorepo



Index: llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
--- llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -3333,10 +3333,6 @@
     LLT Ty = MRI.getType(Res);
     // Lower (G_FSUB LHS, RHS) to (G_FADD LHS, (G_FNEG RHS)).
-    // First, check if G_FNEG is marked as Lower. If so, we may
-    // end up with an infinite loop as G_FSUB is used to legalize G_FNEG.
-    if (LI.getAction({G_FNEG, {Ty}}).Action == Lower)
-      return UnableToLegalize;
     auto Neg = MIRBuilder.buildFNeg(Ty, RHS);
     if (MI.getOpcode() == TargetOpcode::G_STRICT_FSUB)

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