[webkit-changes] [WebKit/WebKit] 1ff6d4: [JSC][armv7] Reserve `d14` as a scratch register f...

[jjgriego]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 1ff6d45f35c140efefa6110b5d5a71a872f3821e
      https://github.com/WebKit/WebKit/commit/1ff6d45f35c140efefa6110b5d5a71a872f3821e
  Author: Joseph Griego <jgriego at igalia.com>
  Date:   2023-10-25 (Wed, 25 Oct 2023)

  Changed paths:
    M Source/JavaScriptCore/jit/FPRInfo.h
    M Source/JavaScriptCore/jit/RegisterSet.cpp
    M Source/JavaScriptCore/llint/LowLevelInterpreter.asm
    M Source/JavaScriptCore/offlineasm/arm.rb

  Log Message:
  -----------
  [JSC][armv7] Reserve `d14` as a scratch register for wasm JITs
https://bugs.webkit.org/show_bug.cgi?id=263324

Reviewed by Justin Michaud.

We really need an extra FP scratch register for wasm BBQ on armv7. In
particular, we use the `nonPreservedNonArgumentFPR0` for this purpose, but we
also ended up using register currently singled out as the
`nonPreservedNonArgumentFPR0`, `d7` as an argument register in BBQ JIT contexts.

To avoid the overlap, reserve `d14` as a scratch register--we copy exactly the
approach used to reserve `d15` as a scratch FPR for the macroassembler [1]:
though the register is callee-save in the platform ABI, we save/restore only at
VM entry/exit and the register is volatile in VM contexts.

[1] https://commits.webkit.org/250952@main

* Source/JavaScriptCore/jit/FPRInfo.h:
* Source/JavaScriptCore/jit/RegisterSet.cpp:
(JSC::RegisterSetBuilder::vmCalleeSaveRegisters):
* Source/JavaScriptCore/llint/LowLevelInterpreter.asm:
* Source/JavaScriptCore/offlineasm/arm.rb:

Canonical link: https://commits.webkit.org/269762@main