Fix a bug that warnings generated with -M or -MM flags

[yamaguchi]

Summary

This is a patch for bug [1]

Warnings should not be emitted with -M and -MM flags, because this mode is only used for generate MakeFiles.

[1]:
https://bugs.llvm.org/show_bug.cgi?id=6817

[v.g.vassilev]

Could you add a test case?

[yamaguchi]

Add testcase.

[v.g.vassilev]

LGTM modulo the comments.

test/Driver/m_and_mm.c

7

Typo.

[yamaguchi]

Fixed typo.

[teemperor]

This also disables warnings for -MD and -MMD which shouldn't happen as we're actually compiling code here and are probably compiling a project. E.g. for people that use this mode to create dependency files while initially building (to figure out when to rebuild each object), this will effectively force -w to the whole build process which is not good.

I would just manually check for -M and -MM where we only run the preprocessor and where adding -w is safe. Also please add another test that we actually get the warnings for -MD and another one for -MMD.

Otherwise this look good.

[yamaguchi]

@teemperor
Do you think it is not a good idea to change condition if -MD or -MMD exists?
for example,
if ( !A->getOption().matches(options::OPT_MD) && !A->getOption().matches(options::OPT_MMD)) CmdArgs.push_back("-w");

[v.g.vassilev]

I think you will see the issue if you add a negative test case, too. I.e. as Raphael said in -MD and -MMD mode we should be able to see warnings.

[yamaguchi]

show warnings with -M and -MD

[yamaguchi]

Add testcase

[v.g.vassilev]

@teemperor, is this ok with you?

[yamaguchi]

@teemperor ping..?

[teemperor]

LGTM, good job! (Sorry for the delay, I think I got interrupted here by the GSoC start...)

[yamaguchi]

Landed in r305561.

lib/Driver/ToolChains/Clang.cpp

         // Otherwise derive from the base input.
         //
         // FIXME: This should use the computed output file location.
         SmallString<128> P(Inputs[0].getBaseInput());
         llvm::sys::path::replace_extension(P, "o");
         DepTarget = Args.MakeArgString(llvm::sys::path::filename(P));
       }
 
+      if (!A->getOption().matches(options::OPT_MD) && !A->getOption().matches(options::OPT_MMD)) {
+        CmdArgs.push_back("-w");
+      }
       CmdArgs.push_back("-MT");
       SmallString<128> Quoted;
       QuoteTarget(DepTarget, Quoted);
       CmdArgs.push_back(Args.MakeArgString(Quoted));
     }
 
     if (A->getOption().matches(options::OPT_M) ||
         A->getOption().matches(options::OPT_MD))

test/Driver/m_and_mm.c

 // RUN: %clang -### \
 // RUN:   -M -MM %s 2> %t
 // RUN: not grep '"-sys-header-deps"' %t
+
+// RUN: %clang -M -MM %s 2> %t
+// RUN: not grep "warning" %t
+
+// RUN: %clang -MMD -MD %s 2> %t
+// RUN: grep "warning" %t
+
+#warning "This warning shouldn't show up with -M and -MM"
+int main (void)
+{
+    return 0;
+}