[llvm] [AArch64][GlobalISel] Look through COPY and G_BITCAST while selecting fcvtl2 (fpext) (PR #65463)

[David Green via llvm-commits]

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@@ -6777,10 +6777,21 @@ AArch64InstructionSelector::selectExtractHigh(MachineOperand &Root) const {
   MachineRegisterInfo &MRI =
       Root.getParent()->getParent()->getParent()->getRegInfo();
 
-  MachineInstr *Extract = getDefIgnoringCopies(Root.getReg(), MRI);
-  if (Extract && Extract->getOpcode() == TargetOpcode::G_UNMERGE_VALUES &&
-      Root.getReg() == Extract->getOperand(1).getReg()) {
-    Register ExtReg = Extract->getOperand(2).getReg();
+  auto Extract = getDefSrcRegIgnoringCopies(Root.getReg(), MRI);
+  while (Extract && Extract->MI->getOpcode() == TargetOpcode::G_BITCAST)
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davemgreen wrote:

Does this work for big endian? I'm not sure if big endian works for global isel at the moment, but I would prefer not to introduce a lot of subtle cases that assume bitcast does not alter lane layout.

https://github.com/llvm/llvm-project/pull/65463