libLTO: Allow linker to choose context of modules and codegen

Add API for specifying which `LLVMContext` each `lto_module_t` and
`lto_code_gen_t` is in.

In particular, this enables the following flow:

    for (auto &File : Files) {
      lto_module_t M = lto_module_create_in_local_context(File...);
      querySymbols(M);
      lto_module_dispose(M);
    }

    lto_code_gen_t CG = lto_codegen_create_in_local_context();
    for (auto &File : FilesToLink) {
      lto_module_t M = lto_module_create_in_codegen_context(File..., CG);
      lto_codegen_add_module(CG, M);
      lto_module_dispose(M);
    }
    lto_codegen_compile(CG);
    lto_codegen_write_merged_modules(CG, ...);
    lto_codegen_dispose(CG);

This flow has a few benefits.

  - Only one module (two if you count the combined module in the code
    generator) is in memory at a time.

  - Metadata (and constants) from files that are parsed to query symbols
    but not linked into the code generator don't pollute the global
    context.

  - The first for loop can be parallelized, since each module is in its
    own context.

  - When the code generator is disposed, the memory from LTO gets freed.

rdar://problem/18767512

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221733 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 18 insertions, 0 deletions

diff --git a/tools/lto/lto.cpp b/tools/lto/lto.cpp
index 3cc6499bd90..ef37c90ba3b 100644
--- a/tools/lto/lto.cpp
+++ b/tools/lto/lto.cpp
@@ -150,6 +150,24 @@ lto_module_t lto_module_create_from_memory_with_path(const void* mem,
       LTOModule::createFromBuffer(mem, length, Options, sLastErrorString, path));
 }
 
+lto_module_t lto_module_create_in_local_context(const void *mem, size_t length,
+                                                const char *path) {
+  lto_initialize();
+  llvm::TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
+  return wrap(LTOModule::createInLocalContext(mem, length, Options,
+                                              sLastErrorString, path));
+}
+
+lto_module_t lto_module_create_in_codegen_context(const void *mem,
+                                                  size_t length,
+                                                  const char *path,
+                                                  lto_code_gen_t cg) {
+  lto_initialize();
+  llvm::TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
+  return wrap(LTOModule::createInContext(mem, length, Options, sLastErrorString,
+                                         path, &unwrap(cg)->getContext()));
+}
+
 void lto_module_dispose(lto_module_t mod) { delete unwrap(mod); }
 
 const char* lto_module_get_target_triple(lto_module_t mod) {