Bug 126543 – FTL should ascribe range meta-data when loading array.length

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

[Filip Pizlo]

This will allow some interesting optimizations on the LLVM side.

[Filip Pizlo]

Created attachment 221604 [details]
the patch

[Filip Pizlo]

Landed in branch in http://trac.webkit.org/changeset/162299

[Geoffrey Garen]

Comment on attachment 221604 [details]
the patch

View in context: https://bugs.webkit.org/attachment.cgi?id=221604&action=review

r=me

> Source/JavaScriptCore/ftl/FTLCommonValues.cpp:65
> +    , nonNegativeInt32(constInt(int32, 0, SignExtend), constInt(int32, 1ll << 31, SignExtend))

Why the "ll" after the "1"?

[Filip Pizlo]

(In reply to comment #3)
> (From update of attachment 221604 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=221604&action=review
> 
> r=me
> 
> > Source/JavaScriptCore/ftl/FTLCommonValues.cpp:65
> > +    , nonNegativeInt32(constInt(int32, 0, SignExtend), constInt(int32, 1ll << 31, SignExtend))
> 
> Why the "ll" after the "1"?

constInt() takes a long long, so I figured that I'd avoid all ambiguity in the implicit integer casting by just starting out with 1 being a long long.

Also, "1" is a 32-bit int and 2^31 isn't a valid 32-bit int value.  So, 1 << 31 is subject to some overflow rules, and I don't feel like figuring out what exactly they are.  It's one of those things that feels like it might fall under undefined behavior and I don't like having to think about that.