[llvm] [GlobalIsel] Combine freeze (PR #93239)

[Thorsten Schütt via llvm-commits]

================
@@ -144,59 +144,6 @@ bool CombinerHelper::matchExtractVectorElementWithDifferentIndices(
   return false;
 }
 
-bool CombinerHelper::matchExtractVectorElementWithFreeze(
-    const MachineOperand &MO, BuildFnTy &MatchInfo) {
-  MachineInstr *Root = getDefIgnoringCopies(MO.getReg(), MRI);
-  GExtractVectorElement *Extract = cast<GExtractVectorElement>(Root);
-
-  Register Vector = Extract->getVectorReg();
-
-  //
-  //  %bv:_(<2 x s32>) = G_BUILD_VECTOR %arg1(s32), %arg2(s32)
-  //  %freeze:_(<2 x s32>) = G_FREEZE %bv(<2 x s32>)
-  //  %extract:_(s32) = G_EXTRACT_VECTOR_ELT %bv(<2 x s32>), %opaque(s64)
-  //
-  //  -->
-  //
-  //  %bv:_(<2 x s32>) = G_BUILD_VECTOR %arg1(s32), %arg2(s32)
-  //  %extract:_(s32) = G_EXTRACT_VECTOR_ELT %bv(<2 x s32>), %opaque(s64)
-  //  %freeze:_(s32) = G_FREEZE %extract(s32)
-  //
-  //
-
-  // For G_FREEZE, the input and the output types are identical. Moving the
-  // freeze from the Vector into the front of the extract preserves the freeze
-  // semantics. The result is still freeze'd. Furthermore, the Vector register
-  // becomes easier to analyze. A build vector could have been hidden behind the
-  // freeze.
-
-  // We expect a freeze on the Vector register.
-  GFreeze *Freeze = getOpcodeDef<GFreeze>(Vector, MRI);
-  if (!Freeze)
-    return false;
-
-  Register Dst = Extract->getReg(0);
-  LLT DstTy = MRI.getType(Dst);
-
-  // We first have to check for one-use and legality of the freeze.
-  // The type of the extractVectorElement did not change.
-  if (!MRI.hasOneNonDBGUse(Freeze->getReg(0)) ||
-      !isLegalOrBeforeLegalizer({TargetOpcode::G_FREEZE, {DstTy}}))
-    return false;
-
-  Register Index = Extract->getIndexReg();
-
-  // We move the freeze from the Vector register in front of the
-  // extractVectorElement.
-  MatchInfo = [=](MachineIRBuilder &B) {
-    auto Extract =
-        B.buildExtractVectorElement(DstTy, Freeze->getSourceReg(), Index);
-    B.buildFreeze(Dst, Extract);
-  };
-
-  return true;
-}
-
----------------
tschuett wrote:

It was moving the freeze in wrong direction. The push combine pushes the freeze into the operation. This combine was doing the opposite. The DAG had the same combine and removed it as well.

https://github.com/llvm/llvm-project/pull/93239