[all-commits] [llvm/llvm-project] 1fccba: [AArch64][PAC] Eliminate excessive MOVs when compu...

[Anatoly Trosinenko via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1fccba5ca1997db13cfa88f788b7acb8cc300b48
      https://github.com/llvm/llvm-project/commit/1fccba5ca1997db13cfa88f788b7acb8cc300b48
  Author: Anatoly Trosinenko <atrosinenko at accesssoftek.com>
  Date:   2024-11-27 (Wed, 27 Nov 2024)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
    M llvm/lib/Target/AArch64/AArch64InstrInfo.td
    M llvm/test/CodeGen/AArch64/ptrauth-call.ll

  Log Message:
  -----------
  [AArch64][PAC] Eliminate excessive MOVs when computing blend (#115185)

As function calls do not generally preserve X16 and X17, it is beneficial
to allow AddrDisc operand of BLRA instruction to reside in these
registers and make use of this condition when computing the
discriminator.

This can save up to two MOVs in cases such as loading a (signed) virtual
function pointer via a (signed) pointer to vtable, for example

    ldr   x9, [x16]
    mov   x8, x16
    mov   x17, x8
    movk  x17, #34646, lsl #48
    blraa x9, x17

can be simplified to

    ldr   x8, [x16]
    movk  x16, #34646, lsl #48
    blraa x8, x16



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