[CodeGen] Add an option to suppress output of llvm.ident

Summary:
By default Clang outputs its version (including git commit hash, in
case of trunk builds) into object and assembly files. It might be
useful to have an option to disable this, especially for debugging
purposes.
This patch implements new command line flags -Qn and -Qy (the names
are chosen for compatibility with GCC). -Qn disables output of
the 'llvm.ident' metadata string and the 'producer' debug info. -Qy
(enabled by default) does the opposite.

Reviewers: faisalv, echristo, aprantl

Reviewed By: aprantl

Subscribers: aprantl, cfe-commits, JDevlieghere, rogfer01

Differential Revision: https://reviews.llvm.org/D45255

llvm-svn: 330442

clang/include/clang/Driver/Options.td

@@ -396,7 +396,10 @@ def O_flag : Flag<["-"], "O">, Flags<[CC1Option]>, Alias<O>, AliasArgs<["2"]>;
 def Ofast : Joined<["-"], "Ofast">, Group<O_Group>, Flags<[CC1Option]>;
 def P : Flag<["-"], "P">, Flags<[CC1Option]>, Group<Preprocessor_Group>,
   HelpText<"Disable linemarker output in -E mode">;
-def Qn : Flag<["-"], "Qn">, IgnoredGCCCompat;
+def Qy : Flag<["-"], "Qy">, Flags<[CC1Option]>,
+  HelpText<"Emit metadata containing compiler name and version">;
+def Qn : Flag<["-"], "Qn">, Flags<[CC1Option]>,
+  HelpText<"Do not emit metadata containing compiler name and version">;
 def Qunused_arguments : Flag<["-"], "Qunused-arguments">, Flags<[DriverOption, CoreOption]>,
   HelpText<"Don't emit warning for unused driver arguments">;
 def Q : Flag<["-"], "Q">, IgnoredGCCCompat;

clang/include/clang/Frontend/CodeGenOptions.def

@@ -69,6 +69,7 @@ CODEGENOPT(EmitDeclMetadata  , 1, 0) ///< Emit special metadata indicating what
                                      ///< Decl* various IR entities came from.
                                      ///< Only useful when running CodeGen as a
                                      ///< subroutine.
+CODEGENOPT(EmitVersionIdentMetadata , 1, 1) ///< Emit compiler version metadata.
 CODEGENOPT(EmitGcovArcs      , 1, 0) ///< Emit coverage data files, aka. GCDA.
 CODEGENOPT(EmitGcovNotes     , 1, 0) ///< Emit coverage "notes" files, aka GCNO.
 CODEGENOPT(EmitOpenCLArgMetadata , 1, 0) ///< Emit OpenCL kernel arg metadata.

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -577,7 +577,8 @@ void CGDebugInfo::CreateCompileUnit() {
                           remapDIPath(getCurrentDirname()),
                           CSInfo,
                           getSource(SM, SM.getMainFileID())),
-      Producer, LO.Optimize || CGOpts.PrepareForLTO || CGOpts.EmitSummaryIndex,
+      CGOpts.EmitVersionIdentMetadata ? Producer : "",
+      LO.Optimize || CGOpts.PrepareForLTO || CGOpts.EmitSummaryIndex,
       CGOpts.DwarfDebugFlags, RuntimeVers,
       CGOpts.EnableSplitDwarf ? "" : CGOpts.SplitDwarfFile, EmissionKind,
       0 /* DWOid */, CGOpts.SplitDwarfInlining, CGOpts.DebugInfoForProfiling,

clang/lib/CodeGen/CodeGenModule.cpp

@@ -571,7 +571,8 @@ void CodeGenModule::Release() {
   if (DebugInfo)
     DebugInfo->finalize();
 
-  EmitVersionIdentMetadata();
+  if (getCodeGenOpts().EmitVersionIdentMetadata)
+    EmitVersionIdentMetadata();
 
   EmitTargetMetadata();
 }

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4408,6 +4408,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     }
   }
 
+  if (!Args.hasFlag(options::OPT_Qy, options::OPT_Qn, true))
+    CmdArgs.push_back("-Qn");
+
   // -fcommon is the default unless compiling kernel code or the target says so
   bool NoCommonDefault = KernelOrKext || isNoCommonDefault(RawTriple);
   if (!Args.hasFlag(options::OPT_fcommon, options::OPT_fno_common,

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1112,6 +1112,8 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.EmitCheckPathComponentsToStrip = getLastArgIntValue(
       Args, OPT_fsanitize_undefined_strip_path_components_EQ, 0, Diags);
 
+  Opts.EmitVersionIdentMetadata = Args.hasFlag(OPT_Qy, OPT_Qn, true);
+
   return Success;
 }
 

clang/test/CodeGen/no-ident-version.c

@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -emit-llvm -debug-info-kind=limited -o - %s \
+// RUN:   | FileCheck --check-prefix=CHECK-NONE %s
+// RUN: %clang_cc1 -Qn -emit-llvm -debug-info-kind=limited -o - %s \
+// RUN:   | FileCheck --check-prefix=CHECK-QN %s
+// RUN: %clang_cc1 -Qy -emit-llvm -debug-info-kind=limited -o - %s \
+// RUN:   | FileCheck --check-prefix=CHECK-QY %s
+
+// CHECK-NONE: define i32 @main()
+// CHECK-NONE: llvm.ident
+// CHECK-NONE: producer:
+
+// CHECK-QN: define i32 @main()
+// CHECK-QN-NOT: llvm.ident
+// CHECK-QN-NOT: producer:
+
+// CHECK-QY: define i32 @main()
+// CHECK-QY: llvm.ident
+// CHECK-QY: producer:
+int main(void) {}