Teach LTOModule to emit linker flags for dllexported symbols, plus interface cleanup.

This change unifies how LTOModule and the backend obtain linker flags
for globals: via a new TargetLoweringObjectFile member function named
emitLinkerFlagsForGlobal. A new function LTOModule::getLinkerOpts() returns
the list of linker flags as a single concatenated string.

This change affects the C libLTO API: the function lto_module_get_*deplibs now
exposes an empty list, and lto_module_get_*linkeropts exposes a single element
which combines the contents of all observed flags. libLTO should never have
tried to parse the linker flags; it is the linker's job to do so. Because
linkers will need to be able to parse flags in regular object files, it
makes little sense for libLTO to have a redundant mechanism for doing so.

The new API is compatible with the old one. It is valid for a user to specify
multiple linker flags in a single pragma directive like this:

 #pragma comment(linker, "/defaultlib:foo /defaultlib:bar")

The previous implementation would not have exposed
either flag via lto_module_get_*deplibs (as the test in
TargetLoweringObjectFileCOFF::getDepLibFromLinkerOpt was case sensitive)
and would have exposed "/defaultlib:foo /defaultlib:bar" as a single flag via
lto_module_get_*linkeropts. This may have been a bug in the implementation,
but it does give us a chance to fix the interface.

Differential Revision: http://reviews.llvm.org/D10548

llvm-svn: 241010

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/include/llvm-c/lto.h b/llvm/include/llvm-c/lto.h
index 9f37dd71e31..0ccb0e9a584 100644
--- a/llvm/include/llvm-c/lto.h
+++ b/llvm/include/llvm-c/lto.h
@@ -282,6 +282,8 @@ lto_module_get_symbol_attribute(lto_module_t mod, unsigned int index);
 /**
  * Returns the number of dependent libraries in the object module.
  *
+ * Deprecated. Now returns an empty list.
+ *
  * \since LTO_API_VERSION=8
  */
 extern unsigned int
@@ -291,6 +293,8 @@ lto_module_get_num_deplibs(lto_module_t mod);
 /**
  * Returns the ith dependent library in the module.
  *
+ * Deprecated. Now always returns null.
+ *
  * \since LTO_API_VERSION=8
  */
 extern const char*
@@ -300,6 +304,9 @@ lto_module_get_deplib(lto_module_t mod, unsigned int index);
 /**
  * Returns the number of linker options in the object module.
  *
+ * Each linker option may consist of multiple flags. It is the linker's
+ * responsibility to split the flags using a platform-specific mechanism.
+ *
  * \since LTO_API_VERSION=8
  */
 extern unsigned int
@@ -309,6 +316,9 @@ lto_module_get_num_linkeropts(lto_module_t mod);
 /**
  * Returns the ith linker option in the module.
  *
+ * Each linker option may consist of multiple flags. It is the linker's
+ * responsibility to split the flags using a platform-specific mechanism.
+ *
  * \since LTO_API_VERSION=8
  */
 extern const char*