[PATCH] D114023: [Driver] Pass --fix-cortex-a53-843419 automatically on Fuchsia

Roland McGrath via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Tue Nov 30 10:52:30 PST 2021

mcgrathr accepted this revision.
mcgrathr added inline comments.
This revision is now accepted and ready to land.

Comment at: clang/lib/Driver/ToolChains/Fuchsia.cpp:91
+    std::string CPU = getCPUName(D, Args, Triple);
+    if (CPU.empty() || CPU == "generic" || CPU == "cortex-a53")
+      CmdArgs.push_back("--fix-cortex-a53-843419");
phosek wrote:
> mcgrathr wrote:
> > How does this relate to -march, -mtune, and/or -mcpu?
> > It's not at all clear to me how we discern automatically when a A53 might be included in the supported target CPU set.  I'm not entirely sure we should have automatic injection in some cases where A53 is a valid target but not all.  That is, if some compiler option combinations that produce code meant to be compatible with an A53 won't automatically get the --fix option, then perhaps it's better to require the explicit --fix option when supporting A53 is the explicit intent.
> This is the same logic as used by the [Gnu driver](https://github.com/llvm/llvm-project/blob/7a7c059d867554e116244ad5639d05d75ed1a7cd/clang/lib/Driver/ToolChains/Gnu.cpp#L451). `getCPUName` only considers `-mcpu`, it ignores `-march` and `-mtune` as far as I can tell.
If the empty or "generic" case is what will apply when no `-mcpu` switch is given regardless of `-march` then I guess this is adequate since we're not really concerned with any architectures older than A53 where someone might use `-mcpu=...` as a proxy for "X and later" where X<A53.

I think this area needs to be more clearly specified and documented eventually, however.  Ideally the determinant would whether the combination of `-march` and/or `-mcpu` switches indicates generating code that is compatible with an A53 CPU, since only if running on an A53 is ruled out should we omit the erratum workaround.

  rG LLVM Github Monorepo



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