[all-commits] [llvm/llvm-project] 54cb6c: [AArch64][PAC] Eliminate excessive MOVs when compu...

[Anatoly Trosinenko via All-commits]

  Branch: refs/heads/users/atrosinenko/pauth-discriminator
  Home:   https://github.com/llvm/llvm-project
  Commit: 54cb6c877d079c968084e2d723666c174fcb873d
      https://github.com/llvm/llvm-project/commit/54cb6c877d079c968084e2d723666c174fcb873d
  Author: Anatoly Trosinenko <atrosinenko at accesssoftek.com>
  Date:   2024-11-06 (Wed, 06 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

As function calls do not generally preserve X16 and X17, it is beneficial
to allow AddrDisc operand of B(L)RA 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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