[compiler-rt] Allow appending to 'target_cflags' value from lit_config.

[abidh]

Summary

This patch is similar to D84708. When testing compiler-rt on different
baremetal targets, it helps to have the ability to pass some more parameters
at test time that allows you to build the test executable for a
given target. For an example, you may need a different linker command
file for different targets.

This patch will allows to do things like

$ llvm-lit --param=append_target_cflags="-T simulator.ld"
or
$ llvm-lit --param=append_target_cflags="-T hardware.ld"

In this way, you can run tests on different targets without having to run
cmake again.

[abidh]

ping.

[delcypher]

This seems reasonable but I do have a few nits.

In general though you probably be better off moving to an approach where you can CMake generate all the configs you want. I realise this might fit your workflow right now so I'm happy to land this patch once we address the nits.

compiler-rt/test/lit.common.cfg.py

581

Nit: Given that this appends rather than replaces you might want to change the name of target_cflags to something like append_target_cflags to avoid confusion.

582

You could add something to print out a message when the append happens. E.g.:

if lit_config_cflags:
  lit_config.note('Appending to extra_cflags: "{}:"'.format(lit_config_cflags))
  extra_cflags += [lit_config_cflags]

583

Why do you append to extra_cflags here? There appear to be other statements after this that append to extra_cflags. My expectation would be the using --param=append_target_cflags="-T simulator.ld" would cause the flags to appended to the very end. My suggestion would be change your code so that it is the very last append to extra_cflags.

[abidh]

Addressed review comments.

[delcypher]

Thanks for addressing my feedback. LGTM

compiler-rt/test/lit.common.cfg.py

 
 if config.use_lto and config.lto_supported:
   run_wrapper += config.lto_launch
   extra_cflags += config.lto_flags
 elif config.use_lto and (not config.lto_supported):
   config.unsupported = True
 
 if config.use_lld and config.has_lld and not config.use_lto:
   extra_cflags += ["-fuse-ld=lld"]
 elif config.use_lld and (not config.has_lld):
   config.unsupported = True
 
+# Append any extra flags passed in lit_config
+append_target_cflags = lit_config.params.get('append_target_cflags', None)
+if append_target_cflags:
+  lit_config.note('Appending to extra_cflags: "{}"'.format(append_target_cflags))
+  extra_cflags += [append_target_cflags]
+
 config.clang = " " + " ".join(run_wrapper + [config.compile_wrapper, config.clang]) + " "
 config.target_cflags = " " + " ".join(target_cflags + extra_cflags) + " "