[PATCH] Fix a bug in IfConverter with nested predicates

[Quentin Colombet]

Ping^2?

-Quentin

On Jul 17, 2013, at 9:27 AM, Quentin Colombet <qcolombet at apple.com> wrote:

> Ping?
> 
> -Quentin
> 
> On Jul 11, 2013, at 4:39 PM, Quentin Colombet <qcolombet at apple.com> wrote:
> 
>> Hi,
>> 
>> Here is a patch that fixes a bug in IfConverter with nested predicates.
>> 
>> The problem seems so obvious that I am wondering if I am missing something.
>> So although the patch is straightforward (one line change), please review carefully.
>> Note: I have tested it with -O3 -arch armv7 (apple iOS) against both SingleSource and Multisource tests.
>> 
>> ** Context **
>> Prior to this patch, IfConverter may widen the cases where a sequence of instructions were executed because of the way it uses nested predicates. This result in incorrect execution.
>> 
>> For instance, Let A be a basic block that flows conditionally into B and B be a predicated block.
>> B can be predicated with A.BrToBPredicate into A iff B.Predicate is less "permissive" than A.BrToBPredicate, i.e., iff A.BrToBPredicate subsumes B.Predicate.
>> 
>> The IfConverter was checking the opposite: B.Predicate subsumes A.BrToBPredicate.
>> 
>> <rdar://problem/14379453>
>> 
>> ** Solution **
>> Check the ‘subsumes’ property correctly.
>> 
>> Thanks for your review.
>> 
>> Cheers,
>> 
>> -Quentin
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