[PATCH] D124836: [AArch64] Add support for -fzero-call-used-regs

Wed May 4 15:42:24 PDT 2022

void added inline comments.

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Comment at: llvm/lib/Target/AArch64/AArch64RegisterInfo.td:1398
+                                 (sequence "W%u", 0, 7))>;
+def FPR8_ARG : RegisterClass<"AArch64", [untyped], 8, (trunc FPR8, 7)> {
+  let Size = 8;
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sdesmalen wrote:
> Should this feature/attribute work with other calling conventions? If so, then it's probably best not to hard-code these values here, but rather to get them from the chosen calling convention for that particular function. The supported calling conventions are defined in AArch64CallingConvention.td.
> 
> For example, you could iterate all registers in GPR64/FPR128/ZPR/PPR register classes and zero their values if they are not marked as callee saved. You can query this information from the call by looking at it's callee-saved regmask (see for example `CSR_AArch64_AAPCS_RegMask` to see how those are defined defined).
Ideally it could be retrieved from the `*CallingConvention.td` files, but in reality it's difficult because those files have a lot of `CCIf...<>` constructs in them, making a simple query complex.

I don't know about the `*_RegMask` thing. Could you explain what it is and how it works?

Repository:
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  https://reviews.llvm.org/D124836/new/

https://reviews.llvm.org/D124836