Emit diagnostic for -munaligned-access on v6m targets

[bfoster]

Summary

Rather than silently disabling unaligned accesses for v6m targets as in the previous patch to llvm, instead produce a warning saying that this architecture doesn't support unaligned accesses.

[bfoster]

As suggested by James, we catch this case in clang rather than silently disabling unaligned accesses in the backend.

[bfoster]

Pinging for review.

[t.p.northover]

Hi,

This seems fine to me. Sorry about the delay.

Tim.

[olista01]

Committed revision 215531.

include/clang/Basic/DiagnosticCommonKinds.td

 
 def err_target_unknown_triple : Error<
   "unknown target triple '%0', please use -triple or -arch">;
 def err_target_unknown_cpu : Error<"unknown target CPU '%0'">;
 def err_target_unknown_abi : Error<"unknown target ABI '%0'">;
 def err_target_unknown_fpmath : Error<"unknown FP unit '%0'">;
 def err_target_unsupported_fpmath : Error<
     "the '%0' unit is not supported with this instruction set">;
+def err_target_unsupported_unaligned : Error<
+  "the %0 sub-architecture does not support unaligned accesses">;
 
 // Source manager
 def err_cannot_open_file : Error<"cannot open file '%0': %1">, DefaultFatal;
 def err_file_modified : Error<
   "file '%0' modified since it was first processed">, DefaultFatal;
 def err_unsupported_bom : Error<"%0 byte order mark detected in '%1', but "
   "encoding is not supported">, DefaultFatal;
 def err_unable_to_rename_temp : Error<

lib/Driver/Tools.cpp

void Clang::AddARMTargetArgs(const ArgList &Args,
 
   // -mkernel implies -mstrict-align; don't add the redundant option.
   if (!KernelOrKext) {
     if (Arg *A = Args.getLastArg(options::OPT_mno_unaligned_access,
                                  options::OPT_munaligned_access)) {
       CmdArgs.push_back("-backend-option");
       if (A->getOption().matches(options::OPT_mno_unaligned_access))
         CmdArgs.push_back("-arm-strict-align");
-      else
+      else {
+        if (getToolChain().getTriple().getSubArch() ==
+            llvm::Triple::SubArchType::ARMSubArch_v6m)
+          D.Diag(diag::err_target_unsupported_unaligned) << "v6m";
         CmdArgs.push_back("-arm-no-strict-align");
       }
     }
+  }
 
   // Setting -mno-global-merge disables the codegen global merge pass. Setting 
   // -mglobal-merge has no effect as the pass is enabled by default.
   if (Arg *A = Args.getLastArg(options::OPT_mglobal_merge,
                                options::OPT_mno_global_merge)) {
     if (A->getOption().matches(options::OPT_mno_global_merge))
       CmdArgs.push_back("-mno-global-merge");
   }