Bug 148649

Summary: DFG AI assertions about not having to do type checks at the point of a Known use kind are unsound
Product: WebKit Reporter: Filip Pizlo <fpizlo>
Component: JavaScriptCoreAssignee: Filip Pizlo <fpizlo>
Severity: Normal    
Priority: P2    
Version: Other   
Hardware: All   
OS: All   
Bug Depends on:    
Bug Blocks: 148610    
Description Flags
the patch sbarati: review+

Description Filip Pizlo 2015-08-31 15:10:33 PDT
We often generate IR like:


It would be valid for any optimization that somehow proves the type of @x to remove the Check node entirely.  But then, AI might fail on an assertion at Foo() because of the KnownInt32 use kind, if AI isn't smart enough to construct the same proof that the former optimization used for removing the Check.

The correct solution is probably to remove the compile-time assertions about Known use kinds having already been checked.  It's OK for those to be debug-only JIT assertions.
Comment 1 Filip Pizlo 2015-08-31 15:11:41 PDT
I might end up fixing this before I do property type inference. It looks like that code might reveal this bug.
Comment 2 Filip Pizlo 2015-09-01 10:42:52 PDT
Created attachment 260369 [details]
the patch
Comment 3 Saam Barati 2015-09-01 10:44:19 PDT
Comment on attachment 260369 [details]
the patch

Comment 4 Filip Pizlo 2015-09-01 11:27:51 PDT
Landed in http://trac.webkit.org/changeset/189219