[llvm] r187761 - Add some comment to LTOCodeGenerator class
Shuxin Yang
shuxin.llvm at gmail.com
Mon Aug 5 17:45:32 PDT 2013
Author: shuxin_yang
Date: Mon Aug 5 19:45:32 2013
New Revision: 187761
URL: http://llvm.org/viewvc/llvm-project?rev=187761&view=rev
Log:
Add some comment to LTOCodeGenerator class
Modified:
llvm/trunk/tools/lto/LTOCodeGenerator.h
Modified: llvm/trunk/tools/lto/LTOCodeGenerator.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/lto/LTOCodeGenerator.h?rev=187761&r1=187760&r2=187761&view=diff
==============================================================================
--- llvm/trunk/tools/lto/LTOCodeGenerator.h (original)
+++ llvm/trunk/tools/lto/LTOCodeGenerator.h Mon Aug 5 19:45:32 2013
@@ -9,6 +9,27 @@
//
// This file declares the LTOCodeGenerator class.
//
+// LTO compilation consists of three phases: Pre-IPO, IPO and Post-IPO.
+//
+// The Pre-IPO phase compiles source code into bitcode file. The resulting
+// bitcode files, along with object files and libraries, will be fed to the
+// linker to through the IPO and Post-IPO phases. By using obj-file extension,
+// the resulting bitcode file disguises itself as an object file, and therefore
+// obviates the need of writing a special set of the make-rules only for LTO
+// compilation.
+//
+// The IPO phase perform inter-procedural analyses and optimizations, and
+// the Post-IPO consists two sub-phases: intra-procedural scalar optimizations
+// (SOPT), and intra-procedural target-dependent code generator (CG).
+//
+// As of this writing, we don't separate IPO and the Post-IPO SOPT. They
+// are intermingled together, and are driven by a single pass manager (see
+// PassManagerBuilder::populateLTOPassManager()).
+//
+// The "LTOCodeGenerator" is the driver for the IPO and Post-IPO stages.
+// The "CodeGenerator" here is bit confusing. Don't confuse the "CodeGenerator"
+// with the machine specific code generator.
+//
//===----------------------------------------------------------------------===//
#ifndef LTO_CODE_GENERATOR_H
@@ -50,10 +71,32 @@ struct LTOCodeGenerator {
_mustPreserveSymbols[sym] = 1;
}
+ // To pass options to the driver and optimization passes. These options are
+ // not necessarily for debugging purpose (The function name is misleading).
+ // This function should be called before LTOCodeGenerator::compilexxx(),
+ // and LTOCodeGenerator::writeMergedModules().
+ //
+ void setCodeGenDebugOptions(const char *opts);
+
bool writeMergedModules(const char *path, std::string &errMsg);
+
+ // Compile the merged module into a *single* object file; the path to object
+ // file is returned to the caller via argument "name". Return *FALSE* on
+ // *SUCCESS*, true otherwise.
+ //
+ // NOTE that it is up to the linker to remove the intermediate object file.
+ // Do not try to remove the object file in LTOCodeGenerator's destructor
+ // as we don't who (LTOCodeGenerator or the obj file) will last longer.
+ //
bool compile_to_file(const char **name, std::string &errMsg);
+
+ // As with compile_to_file(), this function compiles the merged module into
+ // single object file. Instead of returning the object-file-path to the caller
+ // (linker), it brings the object to a buffer, and return the buffer to the
+ // caller. This function should delete intermediate object file once its content
+ // is brought to memory. Return NULL is the compilation was not successful.
+ //
const void *compile(size_t *length, std::string &errMsg);
- void setCodeGenDebugOptions(const char *opts);
private:
void initializeLTOPasses();
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