As reported in PR 13851, clang (trunk r163208) seems to ignore any -MF
option that is used in combination with -E -M or -E -MM. For example:
$ clang -E -MM -MF .depend helloworld.c
clang: warning: argument unused during compilation: '-MF .depend'
and no dependency file is generated, the dependency information is
dumped to standard output instead.
It does work when also compiling, e.g if -MD or -MMD is used:
$ clang -MMD -MF .depend -c helloworld.c
$ cat .depend
helloworld.o: helloworld.c
Looking at Clang::AddPreprocessingOptions() in lib/Driver/Tools.cpp, it
seems the check for a -MF option is done too late: if dependency output
is requested in any way, the DepFile is always the default filename,
which is standard output if -E is used.
I propose the attached patch to fix this.
-Dimitry
Index: tools/clang/lib/Driver/Tools.cpp
===================================================================
--- tools/clang/lib/Driver/Tools.cpp (revision 163208)
+++ tools/clang/lib/Driver/Tools.cpp (working copy)
@@ -219,11 +219,11 @@ void Clang::AddPreprocessingOptions(Compilation &C
(A = Args.getLastArg(options::OPT_MMD))) {
// Determine the output location.
const char *DepFile;
- if (Output.getType() == types::TY_Dependencies) {
- DepFile = Output.getFilename();
- } else if (Arg *MF = Args.getLastArg(options::OPT_MF)) {
+ if (Arg *MF = Args.getLastArg(options::OPT_MF)) {
DepFile = MF->getValue(Args);
C.addFailureResultFile(DepFile);
+ } else if (Output.getType() == types::TY_Dependencies) {
+ DepFile = Output.getFilename();
} else if (A->getOption().matches(options::OPT_M) ||
A->getOption().matches(options::OPT_MM)) {
DepFile = "-";
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