[PATCH] Support using sample profiles with partial debug info.

[David Blaikie]

On Tue, Oct 21, 2014 at 3:31 PM, Diego Novillo <dnovillo at google.com> wrote:

>
>
> On Tue, Oct 21, 2014 at 6:24 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>> ================
>> Comment at: lib/Transforms/Scalar/SampleProfile.cpp:647
>> @@ -645,2 +646,3 @@
>> +                                          const LLVMContext &Ctx) {
>>    NamedMDNode *CUNodes = F.getParent()->getNamedMetadata("llvm.dbg.cu");
>>    if (CUNodes) {
>> ----------------
>> Why do we need this code at all? Should we just remove it in favor of the
>> other code?
>>
>
> I was actually going to ask you.  It seemed to me that this variant might
> be slightly more efficient than the one that does not rely on llvm.dbg.cu?
> (all the insn iteration, I mean).
>

Chances are you'll find it in the first handful of instructions (just past
the prolog) and only have to iterate the entire contents of nodebug
functions (unless anything's been inlined into them, in which case you'll
be able to stop sooner). It may be less work than iterating through (N/2)
subprograms.


> If you don't  think that's the case, then it certainly is simpler if I
> just remove it altogether.
>

Yeah, I'd kill it off unless we one day find this to be a real bottleneck
in which case we can figure out how to make it better (probably by building
the function->subprogram map once & keeping it around for use).
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