[llvm] [AArch64][GlobalISel] Combine G_CONCAT_VECTORS with Illegal Form (PR #85047)

[Amara Emerson via llvm-commits]

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@@ -411,6 +411,44 @@ std::optional<APInt> getCImmOrFPImmAsAPInt(const MachineInstr *MI) {
 
 } // end anonymous namespace
 
+// Checks if a register has been defined by G_IMPLICIT_DEF previously
+bool llvm::isImpDefVRegValWithLookThrough(Register VReg,
+                                          const MachineRegisterInfo &MRI) {
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aemerson wrote:

I'd just move this to the legalizer since it's not going to be used by anything else.

https://github.com/llvm/llvm-project/pull/85047