Add a cc1 option to force disabling lifetime-markers emission from clang

[mehdi_amini]

Summary

This intended as a debugging/development flag only.

[chandlerc]

LGTM

clang/include/clang/Driver/CC1Options.td

 
 def disable_llvm_verifier : Flag<["-"], "disable-llvm-verifier">,
   HelpText<"Don't run the LLVM IR verifier pass">;
 def disable_llvm_passes : Flag<["-"], "disable-llvm-passes">,
   HelpText<"Use together with -emit-llvm to get pristine LLVM IR from the "
            "frontend by not running any LLVM passes at all">;
 def disable_llvm_optzns : Flag<["-"], "disable-llvm-optzns">,
   Alias<disable_llvm_passes>;
+def disable_lifetimemarkers : Flag<["-"], "disable-lifetime-markers">,
+  HelpText<"Disable lifetime-markers emission even when optimizations are "
+           "enabled">;
 def disable_red_zone : Flag<["-"], "disable-red-zone">,
   HelpText<"Do not emit code that uses the red zone.">;
 def dwarf_column_info : Flag<["-"], "dwarf-column-info">,
   HelpText<"Turn on column location information.">;
 def split_dwarf : Flag<["-"], "split-dwarf">,
   HelpText<"Split out the dwarf .dwo sections">;
 def gnu_pubnames : Flag<["-"], "gnu-pubnames">,
   HelpText<"Emit newer GNU style pubnames">;

clang/include/clang/Frontend/CodeGenOptions.def

 CODEGENOPT(UniqueSectionNames, 1, 1) ///< Set for -funique-section-names.
 CODEGENOPT(DisableFPElim     , 1, 0) ///< Set when -fomit-frame-pointer is enabled.
 CODEGENOPT(DisableFree       , 1, 0) ///< Don't free memory.
 CODEGENOPT(DiscardValueNames , 1, 0) ///< Discard Value Names from the IR (LLVMContext flag)
 CODEGENOPT(DisableGCov       , 1, 0) ///< Don't run the GCov pass, for testing.
 CODEGENOPT(DisableLLVMPasses , 1, 0) ///< Don't run any LLVM IR passes to get
                                      ///< the pristine IR generated by the
                                      ///< frontend.
+CODEGENOPT(DisableLifetimeMarkers, 1, 0) ///< Don't emit any lifetime markers
 CODEGENOPT(ExperimentalNewPassManager, 1, 0) ///< Enables the new, experimental
                                              ///< pass manager.
 CODEGENOPT(DisableRedZone    , 1, 0) ///< Set when -mno-red-zone is enabled.
 CODEGENOPT(DisableTailCalls  , 1, 0) ///< Do not emit tail calls.
 CODEGENOPT(EmitDeclMetadata  , 1, 0) ///< Emit special metadata indicating what
                                      ///< Decl* various IR entities came from.
                                      ///< Only useful when running CodeGen as a
                                      ///< subroutine.

clang/lib/CodeGen/CodeGenFunction.cpp

 #include "llvm/IR/Operator.h"
 using namespace clang;
 using namespace CodeGen;
 
 /// shouldEmitLifetimeMarkers - Decide whether we need emit the life-time
 /// markers.
 static bool shouldEmitLifetimeMarkers(const CodeGenOptions &CGOpts,
                                       const LangOptions &LangOpts) {
+  if (CGOpts.DisableLifetimeMarkers)
+    return false;
+
   // Asan uses markers for use-after-scope checks.
   if (CGOpts.SanitizeAddressUseAfterScope)
     return true;
 
   // Disable lifetime markers in msan builds.
   // FIXME: Remove this when msan works with lifetime markers.
   if (LangOpts.Sanitize.has(SanitizerKind::Memory))
     return false;

clang/lib/Frontend/CompilerInvocation.cpp

static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   for (const auto &Arg : Args.getAllArgValues(OPT_fdebug_prefix_map_EQ))
     Opts.DebugPrefixMap.insert(StringRef(Arg).split('='));
 
   if (const Arg *A =
           Args.getLastArg(OPT_emit_llvm_uselists, OPT_no_emit_llvm_uselists))
     Opts.EmitLLVMUseLists = A->getOption().getID() == OPT_emit_llvm_uselists;
 
   Opts.DisableLLVMPasses = Args.hasArg(OPT_disable_llvm_passes);
+  Opts.DisableLifetimeMarkers = Args.hasArg(OPT_disable_lifetimemarkers);
   Opts.DisableRedZone = Args.hasArg(OPT_disable_red_zone);
   Opts.ForbidGuardVariables = Args.hasArg(OPT_fforbid_guard_variables);
   Opts.UseRegisterSizedBitfieldAccess = Args.hasArg(
     OPT_fuse_register_sized_bitfield_access);
   Opts.RelaxedAliasing = Args.hasArg(OPT_relaxed_aliasing);
   Opts.StructPathTBAA = !Args.hasArg(OPT_no_struct_path_tbaa);
   Opts.DwarfDebugFlags = Args.getLastArgValue(OPT_dwarf_debug_flags);
   Opts.MergeAllConstants = !Args.hasArg(OPT_fno_merge_all_constants);

clang/test/CodeGen/lifetime2.c

 // RUN: %clang -S -emit-llvm -o - -O2 %s | FileCheck %s -check-prefixes=CHECK,O2
+// RUN: %clang -S -emit-llvm -o - -O2 -Xclang -disable-lifetime-markers %s \
+// RUN:       | FileCheck %s -check-prefixes=CHECK,O0
 // RUN: %clang -S -emit-llvm -o - -O0 %s | FileCheck %s -check-prefixes=CHECK,O0
 
 extern int bar(char *A, int n);
 
 // CHECK-LABEL: @foo
 // O0-NOT: @llvm.lifetime.start
 int foo (int n) {
   if (n) {