[AIX][LTO] Teaching lto-aix-system-assembler Relative Path and Tilde Resolution

[qiongsiwu1]

Summary

The lto-aix-system-assembler currently only understands absolute path. This patch teaches the option so that it can resolve relative paths and tilde.

llvm/lib/LTO/LTOCodeGenerator.cpp

 
 cl::opt<std::string> LTOStatsFile(
     "lto-stats-file",
     cl::desc("Save statistics to the specified file"),
     cl::Hidden);
 
 cl::opt<std::string> AIXSystemAssemblerPath(
     "lto-aix-system-assembler",
-    cl::desc("Absolute path to the system assembler, picked up on AIX only"),
+    cl::desc("Path to a system assembler, picked up on AIX only"),
     cl::value_desc("path"));
 }
 
 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
     : Context(Context), MergedModule(new Module("ld-temp.o", Context)),
       TheLinker(new Linker(*MergedModule)) {
   Context.setDiscardValueNames(LTODiscardValueNames);
   Context.enableDebugTypeODRUniquing();
bool LTOCodeGenerator::useAIXSystemAssembler() {
   return Triple.isOSAIX();
 }
 
 bool LTOCodeGenerator::runAIXSystemAssembler(SmallString<128> &AssemblyFile) {
   assert(useAIXSystemAssembler() &&
          "Runing AIX system assembler when integrated assembler is available!");
 
   // Set the system assembler path.
-  std::string AssemblerPath(llvm::AIXSystemAssemblerPath.empty()
-                                ? "/usr/bin/as"
-                                : llvm::AIXSystemAssemblerPath.c_str());
+  SmallString<256> AssemblerPath("/usr/bin/as");
+  if (!llvm::AIXSystemAssemblerPath.empty()) {
+    if (llvm::sys::fs::real_path(llvm::AIXSystemAssemblerPath, AssemblerPath,
+                                 /* expand_tilde */ true)) {
+      emitError(
+          "Cannot find the assembler specified by lto-aix-system-assembler");
+      return false;
+    }
+  }
 
   // Prepare inputs for the assember.
   const auto &Triple = TargetMach->getTargetTriple();
   const char *Arch = Triple.isArch64Bit() ? "-a64" : "-a32";
   std::string ObjectFileName(AssemblyFile);
   ObjectFileName[ObjectFileName.size() - 1] = 'o';
   SmallVector<StringRef, 8> Args = {
       "/bin/env",     "LDR_CNTRL=MAXDATA32=0x80000000@${LDR_CNTRL}",