[LLVMdev] Proposal : Function Notes
kledzik at apple.com
Mon Aug 25 23:02:21 PDT 2008
On Aug 25, 2008, at 4:03 PM, Devang Patel wrote:
>> These seem like great default parameters for code-gen, but looking
>> forward, if we also allowed some optimization flags to be specified
>> at LTO time, how would they interact?
> The flags specified on the linker command line during LTO are not
> encoded into llvm IR. However, IMO, these linker command line flags
> should override notes encoded in llvm IR. We may have to handle
> special cases, but we should document linker's decision choices
It is not clear to me which should override which.
For instance, instance, if I compiled with -Os or -O3 then I am
forcing the codegen model at compile time, and the function IR would
have the appropriate opt-size or opt-speed note. But if I specify
neither at llvm-gcc time, the function IR should have neither opt-size
or opt-speed note. At LTO time, I could specify -Os or -O3 (or
equivalent) and it would make sense that the optimizer would use the
opt-size or opt-speed from each function if there, or if none, inherit
the default optimization goal from the link line.
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