[PATCH] D153098: [AArch64] Emit fewer CFI instructions for synchronous unwind tables

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added inline comments.


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Comment at: llvm/test/CodeGen/AArch64/addsub-constant-folding.ll:363
 ; CHECK-NEXT:    sub sp, sp, #32
-; CHECK-NEXT:    .cfi_def_cfa_offset 32
 ; CHECK-NEXT:    str x30, [sp, #16] // 8-byte Folded Spill
+; CHECK-NEXT:    .cfi_def_cfa_offset 32
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ikudrin wrote:
> MaskRay wrote:
> > `.cfi_def_cfa_offset 32` move like this seems unnecessary. It degrades precision without reducing the number of CFI instructions for sync.
> The goal is to reduce the size of the unwind table, not just the number of CFI instructions. Having only one chunk removes `DWA_CFA_advance_loc` instructions that would otherwise be required.
Yes, the goal is fine. However, when the number of instructions does not change, it would be better not to degrade the precision by moving `.cfi_def_cfa_offset`...


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  https://reviews.llvm.org/D153098/new/

https://reviews.llvm.org/D153098