https://github.com/banach-space commented:
I think that what's being proposed here is quite non-standard. In particular,
what should happen here:
```bash
flang-new {A very long list of options copied from somewhere, including
-fno-alias-analysis) -O3 file.f90
```
How is the user meant to know that they need to add `-falias-analysis` at the
end to enable alias analysis? And in general, how are they supposed to know
that `-fno-alias-analysis` overrides `-O3`?
If it was the case of "the last relevant option takes priority" (as is the case
with most/all options) then that would be easy - identical logic would always
apply.
This should be easy to fix if you use this instead of what's currently
implemented (apologies for GitHub being unable to format this properly):
```cpp
Args.getLastArg(options::OPT_falias_analysis,
options::OPT_fno_alias_analysis,
options::OPT_Ofast,
options::OPT_O,
options::OPT_O4);
```
(I'm skipping other changes that would also be required - hopefully this is
clear enough). This should still give you all the flexibility that you need for
testing and be less surprising for end users.
If you are in a rush to land this then this LGTM, but I would like the
relationship between `-O{1|2|3|4}` and `-f{no}-alias-analysis` to be refined in
a follow-up patch. Unless there's a good reason to avoid that? WDYT?
Sorry, I've only really realised this after @tblah updated
[falias-analysis.f90](https://github.com/llvm/llvm-project/pull/73111/files#diff-9e3d54cea408f6f309c22f64040afb821ceba52f3b73e2001b3a4b72114f2a10).
https://github.com/llvm/llvm-project/pull/73111
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