[clang] [llvm] [LLVMABI][AARCH64] Handle condtions for ignoring empty types (PR #224476)

[Madhur Amilkanthwar via cfe-commits]

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@@ -144,12 +148,25 @@ ArgInfo AArch64TargetInfo::classifyArgumentType(
                                            RecordArgABI::RAA_DirectInMemory);
   }
 
+  // Empty records:
+  // AAPCS64 does not say that empty records are ignored as arguments,
+  // but other compilers do so in certain situations, and we copy that behavior.
+  // Those situations are in fact language-mode-specific, which seems really
+  // unfortunate, but it's something we just have to accept. If this doesn't
+  // apply, just fall through to the standard argument-handling path.
+  // Darwin overrides the psABI here to ignore all empty records in all modes.
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madhur13490 wrote:

nit: this sentence explains the isDarwinPCS() check on line 162, but it's sitting five lines above the size computation. Reads better moved down next to the branch it describes.

https://github.com/llvm/llvm-project/pull/224476