Bug 153046 – The StringFromCharCode DFG intrinsic should support untyped operands.

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Mark Lam]

The current StringFromCharCode DFG intrinsic assumes that its operand charCode must be an Int32.  This results in 26000+ BadType OSR exits in the LongSpider crypto-aes benchmark.  With support for Untyped operands, the number of OSR exits drops to 202.

[Mark Lam]

Created attachment 268828 [details]
proposed patch.

The patch passes the JSC tests.  However, still need to run benchmarks on them.

[Mark Lam]

Created attachment 268872 [details]
x86_64 benchmark result.

[Mark Lam]

Created attachment 268873 [details]
x86 benchmark results.

[Mark Lam]

The benchmarks shows that perf is neutral with this patch.  All of the differences are due to noise (does not repeat on retry) except for one: ftl-polymorphic-StringFromCharCode which I just added for this patch:

   ftl-polymorphic-StringFromCharCode               246.9686+-17.4090    ^    207.8919+-11.0696       ^ definitely 1.1880x faster

This is only for 64 bit x86_64 though.  It does not manifest on x86 because there appears to be a bug on 32-bit where the StringFromCharCode intrinsic is not recognized and therefore not deployed: https://bugs.webkit.org/show_bug.cgi?id=153066.

This patch is ready for a review.

[Geoffrey Garen]

Comment on attachment 268828 [details]
proposed patch.

View in context: https://bugs.webkit.org/attachment.cgi?id=268828&action=review

r=me

> Source/JavaScriptCore/dfg/DFGOperations.cpp:1316
> +EncodedJSValue JIT_OPERATION operationStringFromValueCharCode(ExecState* exec, EncodedJSValue encodedValue)

I would call this operationStringFromCharCodeUntyped.

If we have to do this in more cases, we should create an operationToUInt32 instead.

[Mark Lam]

Thanks for the review.  Landed in r194996: <http://trac.webkit.org/r194996>.