Make .file directive to have basename only

[twoh]

Summary

Currently LLVM puts directory along with the filename in .file directive, but this behavior doesn't match gcc. There's a no clear description about which one is right (https://sourceware.org/binutils/docs/as/File.html#File), but one document (https://sourceware.org/gdb/current/onlinedocs/stabs/ELF-Linker-Relocation.html) suggests that STT_FILE symbol in elf file is expected to have basename only, which should have a same sting file .file directive according to (https://docs.oracle.com/cd/E26502_01/html/E28388/eoiyg.html).

This also affects badly on the build system that uses hashing, as the directory info could be differnt from developer to developer even when they're working on same file.

[twoh]

Delete unnecessary line from the test.

[twoh]

Ping. Thanks!

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

 #include "llvm/MC/MCValue.h"
 #include "llvm/MC/SectionKind.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/Timer.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetFrameLowering.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetLoweringObjectFile.h"
 #include "llvm/Target/TargetMachine.h"
bool AsmPrinter::doInitialization(Module &M) {
 
   // Allow the target to emit any magic that it wants at the start of the file.
   EmitStartOfAsmFile(M);
 
   // Very minimal debug info. It is ignored if we emit actual debug info. If we
   // don't, this at least helps the user find where a global came from.
   if (MAI->hasSingleParameterDotFile()) {
     // .file "foo.c"
-    OutStreamer->EmitFileDirective(M.getSourceFileName());
+    OutStreamer->EmitFileDirective(
+        llvm::sys::path::filename(M.getSourceFileName()));
   }
 
   GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();
   assert(MI && "AsmPrinter didn't require GCModuleInfo?");
   for (auto &I : *MI)
     if (GCMetadataPrinter *MP = GetOrCreateGCPrinter(*I))
       MP->beginAssembly(M, *MI, *this);
 

test/CodeGen/X86/file-directive.ll

+; RUN: llc -mtriple=x86_64-linux-gnu -filetype=asm < %s | FileCheck %s --check-prefix=DIRECTIVE
+; RUN: llc -mtriple=x86_64-linux-gnu -filetype=obj < %s | llvm-readobj -symbols | FileCheck %s --check-prefix=STT-FILE
+
+; DIRECTIVE: .file "foobar"
+; STT-FILE: Name: foobar
+; STT-FILE-NEXT: Value: 0x0
+; STT-FILE-NEXT: Size: 0
+; STT-FILE-NEXT: Binding: Local
+; STT-FILE-NEXT: Type: File
+; STT-FILE-NEXT: Other: 0
+; STT-FILE-NEXT: Section: Absolute
+; STT-FILE-NOT: Name:
+
+source_filename = "/path/to/foobar"