[PATCH] D159206: [Clang] Propagate target-features if compatible when using mlink-builtin-bitcode

[Matt Arsenault via Phabricator via cfe-commits]

arsenm added inline comments.


================
Comment at: clang/lib/CodeGen/CGCall.cpp:2030-2031
+      bool EnabledForTarget = TEntry->second;
+      if (EnabledForTarget != EnabledForFunc)
+        return;
+    }
----------------
jmmartinez wrote:
> arsenm wrote:
> > Early return breaks the other features
> I did not understand this remark.
> 
> If the features are not compatible, we do not add a "target-features" entry in the new "FuncAttrs". Then, the old "target-features" entry is kept in the Function coming from the builtin.
> 
> If you think it would be better to set the target-features in FuncAttrs to the old value in any case. If that's the case I've added the following code:
> 
>     if (EnabledForTarget != EnabledForFunc) {
>         FuncAttr.addAttribute(FFeatures);
>         return;
>     }
You find an incompatible feature and then discontinue processing any further features by early exiting. I expect this to act like an append to any features already present. The incompatibility is at an individual feature level, not the group 


================
Comment at: clang/lib/CodeGen/CGCall.cpp:2034
+  }
+
+  FuncAttr.addAttribute("target-features", llvm::join(MergedFeatures, ","));
----------------
jmmartinez wrote:
> arsenm wrote:
> > Really it would be less bad if the incompatible functions were not imported rather than the backend pass
> I thought it was possible to have functions with incompatible features in the same module. 
> e.g. one function compiled with some instruction set support, one without, and an ifunc that resolves to one or the other.
> 
> Maybe it's not the case in the context of `-mlink-builtin-bitcode`?
The truth is this system isn't really well considered. We don't have real ifunc support and we probably shouldn't be using subtargets for cases with incompatible encodings 


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  https://reviews.llvm.org/D159206/new/

https://reviews.llvm.org/D159206