[clang][deps] Reset some benign codegen options

[jansvoboda11]

Summary

Some command-line codegen arguments are likely to differ between identical modules discovered from different translation units. This patch removes them to make builds deterministic and/or reduce the number of built modules.

[Bigcheese]

lgtm

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

CompilerInvocation ModuleDepCollector::makeInvocationForModuleBuildWithoutPaths(
     const ModuleDeps &Deps,
     llvm::function_ref<void(CompilerInvocation &)> Optimize) const {
   // Make a deep copy of the original Clang invocation.
   CompilerInvocation CI(OriginalInvocation);
 
   CI.getLangOpts()->resetNonModularOptions();
   CI.getPreprocessorOpts().resetNonModularOptions();
 
-  // Remove options incompatible with explicit module build.
+  // Remove options incompatible with explicit module build or are likely to
+  // differ between identical modules discovered from different translation
+  // units.
   CI.getFrontendOpts().Inputs.clear();
   CI.getFrontendOpts().OutputFile.clear();
+  CI.getCodeGenOpts().MainFileName.clear();
+  CI.getCodeGenOpts().DwarfDebugFlags.clear();
 
   CI.getFrontendOpts().ProgramAction = frontend::GenerateModule;
   CI.getLangOpts()->ModuleName = Deps.ID.ModuleName;
   CI.getFrontendOpts().IsSystemModule = Deps.IsSystem;
 
   CI.getLangOpts()->ImplicitModules = false;
 
   // Report the prebuilt modules this module uses.

clang/test/ClangScanDeps/Inputs/removed-args/cdb.json.template

 [
   {
     "directory": "DIR",
-    "command": "clang -fsyntax-only DIR/tu.c -fmodules -fimplicit-module-maps -fmodules-cache-path=DIR/cache -include DIR/header.h -o DIR/tu.o",
+    "command": "clang -fsyntax-only DIR/tu.c -fmodules -fimplicit-module-maps -fmodules-cache-path=DIR/cache -include DIR/header.h -grecord-command-line -o DIR/tu.o",
     "file": "DIR/tu.c"
   }
 ]

clang/test/ClangScanDeps/removed-args.c

 // Some command-line arguments used for compiling translation units are not
-// compatible with the semantics of modules and should be removed. In this test
-// case, the command-lines for modules should drop the '-include' argument.
+// compatible with the semantics of modules or are likely to differ between
+// identical modules discovered from different translation units. This test
+// checks such arguments are removed from the command-lines: '-include',
+// '-dwarf-debug-flag' and '-main-file-name'.
 
 // RUN: rm -rf %t && mkdir %t
 // RUN: cp %S/Inputs/removed-args/* %t
 
 // RUN: sed "s|DIR|%/t|g" %S/Inputs/removed-args/cdb.json.template > %t/cdb.json
 // RUN: echo -%t > %t/result.json
 // RUN: clang-scan-deps -compilation-database %t/cdb.json -format experimental-full >> %t/result.json
 // RUN: cat %t/result.json | sed 's:\\\\\?:/:g' | FileCheck %s
 //
 // CHECK:      -[[PREFIX:.*]]
 // CHECK-NEXT: {
 // CHECK-NEXT:   "modules": [
 // CHECK-NEXT:     {
 // CHECK-NEXT:       "clang-module-deps": [],
 // CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/module.modulemap",
 // CHECK-NEXT:       "command-line": [
 // CHECK-NEXT:         "-cc1"
+// CHECK-NOT:          "-dwarf-debug-flags"
+// CHECK-NOT:          "-main-file-name"
 // CHECK-NOT:          "-include"
 // CHECK:            ],
 // CHECK-NEXT:       "context-hash": "[[HASH_MOD_HEADER:.*]]",
 // CHECK-NEXT:       "file-deps": [
 // CHECK-NEXT:         "[[PREFIX]]/mod_header.h",
 // CHECK-NEXT:         "[[PREFIX]]/module.modulemap"
 // CHECK-NEXT:       ],
 // CHECK-NEXT:       "name": "ModHeader"