Remove a gross usage of environment variables in MachineVerifier, replacing it with support for setting the -verify-machineinstrs flag via an environment variable in LIT.

[resistor]

Summary

This preserves the handy functionality of force-enabling the MachineVerifier, without the need to embed usage of environment variables in LLVM client applications.

[chandlerc]

This looks great. Minor nit below, but submit whenever.

lib/CodeGen/MachineVerifier.cpp

66

From the other review, make this a reference? (Maybe that doesn't work with some other constructor.

[resistor]

r228075

lib/CodeGen/MachineVerifier.cpp

     MachineVerifier(Pass *pass, const char *b) :
       PASS(pass),
       Banner(b),
-      OutFileName(getenv("LLVM_VERIFY_MACHINEINSTRS"))
+      OS(&errs())
       {}
 
     bool runOnMachineFunction(MachineFunction &MF);
 
     Pass *const PASS;
     const char *Banner;
-    const char *const OutFileName;
     raw_ostream *OS;
     const MachineFunction *MF;
     const TargetMachine *TM;

 }
 
 bool MachineVerifier::runOnMachineFunction(MachineFunction &MF) {
-  raw_ostream *OutFile = nullptr;
-  if (OutFileName) {
-    std::error_code EC;
-    OutFile = new raw_fd_ostream(OutFileName, EC,
-                                 sys::fs::F_Append | sys::fs::F_Text);
-    if (EC) {
-      errs() << "Error opening '" << OutFileName << "': " << EC.message()
-             << '\n';
-      exit(1);
-    }
-
-    OS = OutFile;
-  } else {
-    OS = &errs();
-  }
-
   foundErrors = 0;
 
   this->MF = &MF;

   }
   visitMachineFunctionAfter();
 
-  if (OutFile)
-    delete OutFile;
-  else if (foundErrors)
+  if (foundErrors)
     report_fatal_error("Found "+Twine(foundErrors)+" machine code errors.");
 
   // Clean up.

lib/CodeGen/Passes.cpp

     cl::desc("Dump garbage collector data"));
 static cl::opt<bool> VerifyMachineCode("verify-machineinstrs", cl::Hidden,
     cl::desc("Verify generated machine code"),
-    cl::init(getenv("LLVM_VERIFY_MACHINEINSTRS")!=nullptr));
+    cl::init(false),
+    cl::ZeroOrMore);
+
 static cl::opt<std::string>
 PrintMachineInstrs("print-machineinstrs", cl::ValueOptional,
                    cl::desc("Print machine instrs"),

test/lit.cfg

         # Warn, but still provide a substitution.
         lit_config.note('Did not find ' + tool_name + ' in ' + llvm_tools_dir)
         tool_path = llvm_tools_dir + '/' + tool_name
+    if tool_name == "llc" and os.environ['LLVM_ENABLE_MACHINE_VERIFIER'] == "1":
+        tool_path += " -verify-machineinstrs"
     config.substitutions.append((pattern, tool_pipe + tool_path))
 
 ### Targets