r198640 - CodeGen: Initial instrumentation based PGO implementation

[Chris Lattner]

On Jan 14, 2014, at 9:58 PM, Justin Bogner <mail at justinbogner.com> wrote:

> Chris Lattner <sabre at nondot.org> writes:
>>>>>   -  // If the body of the case is just a 'break', and if there was no
>>>>>   fallthrough,
>>>>>   -  // try to not emit an empty block.
>>>>>   -  if ((CGM.getCodeGenOpts().OptimizationLevel > 0) &&
>>>>>   +  // If the body of the case is just a 'break', try to not emit an empty
>>>>>   block.
>>>>>   +  // If we're profiling or we're not optimizing, leave the block in for
>>>>>   better
>>>>>   +  // debug and coverage analysis.
>>>>>   +  if (!CGM.getCodeGenOpts().ProfileInstrGenerate &&
>>>>>   +      CGM.getCodeGenOpts().OptimizationLevel > 0 &&
>>>>>          isa<BreakStmt>(S.getSubStmt())) {
>>>>>        JumpDest Block = BreakContinueStack.back().BreakBlock;
>> 
>> I don't like clang generating dead code.  This isn't good for -O0
>> compile time because nothing removes them, and we get unnecessarily
>> slow and bloated debug mode code.  However, if we need to drop a
>> profiling counter in a block, that seems like a good reason to emit
>> it.  Do we really need to do this though?  If the block would be
>> elided by -O0 code, why do we care about its count?
> 
> In this particular case, we didn't elide the block at -O0 anyway. It's
> only skipped if optimizations are on, which seems kind of silly since
> the backend will remove it for us.

Ok, I don't have any objection to keeping the block then.

-Chris