[PATCH] D124060: [PowerPC] Enable CR bits support for Power8 and above.

Wed Apr 27 02:42:56 PDT 2022

nemanjai added inline comments.

================
Comment at: clang/lib/Basic/Targets/PPC.cpp:519
                                 .Default(false);
+  Features["crbits"] = llvm::StringSwitch<bool>(CPU)
+                                .Case("ppc64le", true)
----------------
shchenz wrote:
> amyk wrote:
> > shchenz wrote:
> > > If we set the `+crbits` by the arch name, do we still need the customization (Turn on crbits for O2 and above) in `computeFSAdditions()`? 
> > Yeah, that's a good point. I looked into this previously, and it appears that addition of `-mcrbits` inside `computeFSAdditions()` may still be necessary. 
> > 
> > In particular, we have test cases that test pre-POWER8 with optimizations on (or, if no optimization level is provided, then -O2 is assumed the default). In these cases, much of the code changes if the customization inside `computeFSAdditions()` is removed because we would no longer be using crbits pre-P8.
> hmm, OK, then we still have the same issue that this patch fixes for pre-POWER8. I'm ok with leaving it for now as IMO Power7/Power6 should not be major versions for PowerPC.
Up until Power8, the only instructions we had that require `crbits` were CR-logicals (which existed since the POWER architecture - i.e. before PowerPC). In Power8, we added BCD instructions that also require `crbits`. So that's why we turn it on for Power8 and up.

Repository:
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  https://reviews.llvm.org/D124060/new/

https://reviews.llvm.org/D124060