[llvm-commits] [llvm] r151429 - in /llvm/trunk: include/llvm/Transforms/IPO.h include/llvm/Transforms/IPO/InlinerPass.h include/llvm/Transforms/Utils/Cloning.h lib/Transforms/IPO/InlineAlways.cpp lib/Transforms/IPO/InlineSimple.cpp lib/Transforms/IPO/Inliner.cpp lib/Transforms/Utils/InlineFunction.cpp

[Chad Rosier]

On Feb 24, 2012, at 11:22 PM, Duncan Sands wrote:

> Hi Chad,
> 
>> Add support for disabling llvm.lifetime intrinsics in the AlwaysInliner. These
>> are optimization hints, but at -O0 we're not optimizing.  This becomes a problem
>> when the alwaysinline attribute is abused.
>> rdar://10921594
> 
> can you please explain some more for those of us who can't access rdar.  Why is
> it a problem, and what alwaysinline abuse do you have in mind?

At -O0 the AlwaysInliner pass is run to honor the always_inline attribute.  By default the @llvm.lifetime_start and @llvm.lifetime_end intrinsics were being emitted.  These are compiler hints and at -O0 they're never used and thus should not be emitted.  The particular test case I came across was compiling in 283s at -O0 (fast, huh).  Now it compiles in 1.35s at -O0.  By abuse I mean the developer thinks they're smarted then the compiler, so they mark everything with the always_inline attribute.  I'm not saying this is a common problem, but regardless these intrinsics are useless at -O0.

> You also forgot to add a testcase.

Yes, you're right.  I will add one soon.  Thanks for keeping me honest, Duncan.

 Chad

> 
> Ciao, Duncan.
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