[PATCH] D56717: [SLH] AArch64: correctly pick temporary register to mask SP

[Zola Bridges via Phabricator via llvm-commits]

zbrid added inline comments.


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Comment at: llvm/lib/Target/AArch64/AArch64SpeculationHardening.cpp:253
+  llvm_unreachable("The nature of call instructions and the ABI must result in "
+                   "finding at least one register above.");
+}
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Since I don't know much about the ABI or the assumptions around calls, I had some quick questions about this for clarification. Can you be sure that this is unreachable because the way the calling convention is specified means there will always be at least one dead register before a call? For example, since there are several call clobbered registers specified in the calling convention even if x17 is used as an address for an indirect branch instruction (and is therefore live across the call), there's no way for all of the call clobbered registers to be live since there are no call instructions that could force all of them to be live? 


Repository:
  rL LLVM

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  https://reviews.llvm.org/D56717/new/

https://reviews.llvm.org/D56717