[LLVMdev] Different Runtimes using clang-gcc and clang-opt-llc-gcc

[Jim Grosbach]

On Jun 8, 2011, at 5:49 AM, Duncan Sands wrote:

> Hi Suresh,
> 
>> $ clang -O0 -c -flto foo.c
>> $ llc foo.o
> 
> ^ llc defaults to -O2

Yep. Exactly right. Specifically, the code generator and register allocator behave differently at -O0, sacrificing generated code quality to get better debugging information and compile-time performance. That said, running things this way, most of the mid-level optimizations that would normally be applied at -O2 still aren't as they're not part of llc.

> 
>> $ gcc foo.o.s
> 
> Ciao, Duncan.
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