[llvm] [AArch64][GlobalISel] Implement selectVaStartAAPCS (PR #106979)

[Matt Arsenault via llvm-commits]

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@@ -2045,7 +2045,8 @@ bool AArch64InstructionSelector::selectVaStartAAPCS(
                   (*I.memoperands_begin())
                       ->getPointerInfo()
                       .getWithOffset(OffsetBytes),
-                  MachineMemOperand::MOStore, PtrSize, Align(PtrSize)));
+                  MachineMemOperand::MOStore, PtrSize,
+                  commonAlignment(Align(PtrSize), OffsetBytes)));
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arsenm wrote:

Actually I was wrong, the MMO alignment is a function of commonAlignment(BaseAlign, Offset), so this should be passing through the same base alignment from MMO->getBaseAlign() 

https://github.com/llvm/llvm-project/pull/106979