Add the -disable-opt option to LTO. This adds:

- Consistency with opt (which supports the same option with the same meaning and
  description).
- Debugging gold plugin-based linking without optimizations getting in the way.
- Debugging programs linked with the gold plugin while preserving the original
  debug info.
- Fine-grained control over LTO passes using the gold plugin in combination with
  opt (or clang/dragonegg).

Patch by Cristiano Giuffrida!

llvm-svn: 176257

tools/lto/LTOCodeGenerator.cpp

@@ -46,6 +46,10 @@
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
 using namespace llvm;
 
+static cl::opt<bool>
+DisableOpt("disable-opt", cl::init(false),
+  cl::desc("Do not run any optimization passes"));
+
 static cl::opt<bool>
 DisableInline("disable-inlining", cl::init(false),
   cl::desc("Do not run the inliner pass"));
@@ -376,10 +380,12 @@ bool LTOCodeGenerator::generateObjectFile(raw_ostream &out,
   // Enabling internalize here would use its AllButMain variant. It
   // keeps only main if it exists and does nothing for libraries. Instead
   // we create the pass ourselves with the symbol list provided by the linker.
-  PassManagerBuilder().populateLTOPassManager(passes,
+  if (!DisableOpt) {
+    PassManagerBuilder().populateLTOPassManager(passes,
                                               /*Internalize=*/false,
                                               !DisableInline,
                                               DisableGVNLoadPRE);
+  }
 
   // Make sure everything is still good.
   passes.add(createVerifierPass());