[Clang] Add option to disable -mconstructor-aliases with -mno-constructor-aliases

[modimo]

Summary

We've found that when profiling, counts are only generated for the real definition of constructor aliases (C2 in mangled name). However, when compiling the C1 version is present at the callsite and leads to a lack of counts due to this aliasing. This causes us to miss out on inlining an otherwise hot constructor.

-mconstructor-aliases is AFAICT an optimization, so having a disabling flag if wanted seems valuable.

Testing:
ninja check-all

[wenlei]

clang/include/clang/Driver/Options.td

5069–5072

nit: use two lines for consistency. check sanitize_stats, sanitize_cfi_cross_dso and others.

[modimo]

Condense lines

[wenlei]

lgtm, thanks

clang/include/clang/Driver/Options.td

def mregparm : Separate<["-"], "mregparm">,
   HelpText<"Limit the number of registers available for integer arguments">,
   MarshallingInfoInt<CodeGenOpts<"NumRegisterParameters">>;
 def msmall_data_limit : Separate<["-"], "msmall-data-limit">,
   HelpText<"Put global and static data smaller than the limit into a special section">,
   MarshallingInfoInt<CodeGenOpts<"SmallDataLimit">>;
 def funwind_tables_EQ : Joined<["-"], "funwind-tables=">,
   HelpText<"Generate unwinding tables for all functions">,
   MarshallingInfoInt<CodeGenOpts<"UnwindTables">>;
-def mconstructor_aliases : Flag<["-"], "mconstructor-aliases">,
-  HelpText<"Emit complete constructors and destructors as aliases when possible">,
-  MarshallingInfoFlag<CodeGenOpts<"CXXCtorDtorAliases">>;
+defm constructor_aliases : BoolOption<"m", "constructor-aliases",
+  CodeGenOpts<"CXXCtorDtorAliases">, DefaultFalse,
+  PosFlag<SetTrue, [], "Enable">, NegFlag<SetFalse, [], "Disable">,
+  BothFlags<[CC1Option], " emitting complete constructors and destructors as aliases when possible">>;
 def mlink_bitcode_file : Separate<["-"], "mlink-bitcode-file">,
   HelpText<"Link the given bitcode file before performing optimizations.">;
 def mlink_builtin_bitcode : Separate<["-"], "mlink-builtin-bitcode">,
   HelpText<"Link and internalize needed symbols from the given bitcode file "
            "before performing optimizations.">;
 def mlink_cuda_bitcode : Separate<["-"], "mlink-cuda-bitcode">,
   Alias<mlink_builtin_bitcode>;
 def vectorize_loops : Flag<["-"], "vectorize-loops">,
   HelpText<"Run the Loop vectorization passes">,

clang/test/CodeGenCXX/constructor-alias.cpp

-// RUN: %clang_cc1 -emit-llvm -triple mipsel--linux-gnu -mconstructor-aliases -o - %s | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm -triple mipsel--linux-gnu -mno-constructor-aliases -mconstructor-aliases -o - %s | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm -triple mipsel--linux-gnu -mconstructor-aliases -mno-constructor-aliases -o - %s | FileCheck %s --check-prefix=NO-ALIAS
 
 // The target attribute code used to get confused with aliases. Make sure
 // we don't crash when an alias is used.
 
 struct B {
   B();
 };
 B::B() {
 }
 
 // CHECK: @_ZN1BC1Ev ={{.*}} unnamed_addr alias void (%struct.B*), void (%struct.B*)* @_ZN1BC2Ev
+// NO-ALIAS-NOT: @_ZN1BC1Ev ={{.*}} unnamed_addr alias void (%struct.B*), void (%struct.B*)* @_ZN1BC2Ev