Bug 125653 – CStack Branch: Eliminate unnecessary add/sub 16 to stack pointer

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Michael Saboff]

The DFG call out code constructs a new callee frame relative to the stack pointer.  Currently before making a call, it decrements the stack pointer by 16 to have it point above the returnPC and caller frame slots.  Instead, the stack pointer should be set properly at the top of the function so that the callee frame above the returnPC can be constructed relative to the stack pointer and then issue a call without adjusting the stack pointer.

[Michael Saboff]

Created attachment 219122 [details]
Patch

[Michael Saboff]

Landed in 160506 on the jsCStack branch: <http://trac.webkit.org/160506>

[Geoffrey Garen]

Comment on attachment 219122 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=219122&action=review

r=me

> Source/JavaScriptCore/dfg/DFGGraph.cpp:706
> +    unsigned result = m_nextMachineLocal + std::max(m_parameterSlots, (unsigned)JSStack::CallerFrameAndPCSize);

static_cast, please.

> Source/JavaScriptCore/dfg/DFGGraph.cpp:707
>      result += result & 1; // Align the register count

This would be better expressed as "result = roundUpToMultipleOf<stackAlignment>(result);", and no comment.

> Source/JavaScriptCore/llint/LowLevelInterpreter.asm:44
> +const CallerFrameAndPCSize = 2 * PtrSize

Please add an ASSERT for this to LLIntData.cpp.

[Michael Saboff]

Changes from review landed in 160514 on the jsCStack branch: <http://trac.webkit.org/160514 >