Bug 119899 – Link failure in DFG

• Status: RESOLVED
• Resolution: CONFIGURATION CHANGED
• Component: JavaScriptCore

[Oliver Hunt]

x = 0;
function h() {
if (x.y++) 
  missing();
}
for (;;) try { h() } catch(e){}

Fails with this assertion:
1   0x10e556e30 WTFCrash
2   0x10e0cf13c JSC::X86Assembler::linkJump(JSC::AssemblerLabel, JSC::AssemblerLabel)
3   0x10e197129 JSC::AbstractMacroAssembler<JSC::X86Assembler>::Jump::linkTo(JSC::AbstractMacroAssembler<JSC::X86Assembler>::Label, JSC::AbstractMacroAssembler<JSC::X86Assembler>*) const
4   0x10e1e5c9c JSC::DFG::SpeculativeJIT::linkBranches()
5   0x10e1e5bdf JSC::DFG::SpeculativeJIT::compile()
6   0x10e191f94 JSC::DFG::JITCompiler::compileBody()
7   0x10e194134 JSC::DFG::JITCompiler::compileFunction()
8   0x10e1ca06b JSC::DFG::Plan::compileInThreadImpl(JSC::DFG::LongLivedState&)
9   0x10e1c9a46 JSC::DFG::Plan::compileInThread(JSC::DFG::LongLivedState&)
10  0x10e2690fc JSC::DFG::Worklist::runThread()
11  0x10e2681f5 JSC::DFG::Worklist::threadFunction(void*)
12  0x10e59ced0 WTF::threadEntryPoint(void*)
13  0x10e59d878 WTF::wtfThreadEntryPoint(void*)
14  0x7fff8c0848a9 _pthread_body
15  0x7fff8c08473a _pthread_struct_init
16  0x7fff8c088fd9 thread_start

[Radar WebKit Bug Importer]

<rdar://problem/14758271>

[Yi Shen]

Created attachment 210815 [details]
proposal patch

[Geoffrey Garen]

Oops! It looks like this patch has been unreviewed for a while.

Neither the attached test case nor the original bug report crash in TOT, so I'll mark this r-. Is there still a reason to emit an explicit ForceOSRExit when we've detected a CFA contradiction?

[Filip Pizlo]

(In reply to comment #3)
> Oops! It looks like this patch has been unreviewed for a while.
> 
> Neither the attached test case nor the original bug report crash in TOT, so I'll mark this r-. Is there still a reason to emit an explicit ForceOSRExit when we've detected a CFA contradiction?

No - I think it would actually be wrong to do it.  We would lose assertion coverage and we would get worse profiling.  The DFG is now very good at handling contradictions like this.