r340439 - Currently clang does not emit unused static constants. GCC emits these
Elizabeth Andrews via cfe-commits
cfe-commits at lists.llvm.org
Wed Aug 22 12:05:19 PDT 2018
Author: eandrews
Date: Wed Aug 22 12:05:19 2018
New Revision: 340439
URL: http://llvm.org/viewvc/llvm-project?rev=340439&view=rev
Log:
Currently clang does not emit unused static constants. GCC emits these
constants by default when there is no optimization.
GCC's option -fno-keep-static-consts can be used to not emit
unused static constants.
In Clang, since default behavior does not keep unused static constants,
-fkeep-static-consts can be used to emit these if required. This could be
useful for producing identification strings like SVN identifiers
inside the object file even though the string isn't used by the program.
Differential Revision: https://reviews.llvm.org/D40925
Added:
cfe/trunk/test/CodeGen/keep-static-consts.cpp
Modified:
cfe/trunk/include/clang/Driver/Options.td
cfe/trunk/include/clang/Frontend/CodeGenOptions.def
cfe/trunk/lib/CodeGen/CodeGenModule.cpp
cfe/trunk/lib/Driver/ToolChains/Clang.cpp
cfe/trunk/lib/Frontend/CompilerInvocation.cpp
Modified: cfe/trunk/include/clang/Driver/Options.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Driver/Options.td?rev=340439&r1=340438&r2=340439&view=diff
==============================================================================
--- cfe/trunk/include/clang/Driver/Options.td (original)
+++ cfe/trunk/include/clang/Driver/Options.td Wed Aug 22 12:05:19 2018
@@ -893,7 +893,8 @@ def fforce_enable_int128 : Flag<["-"], "
def fno_force_enable_int128 : Flag<["-"], "fno-force-enable-int128">,
Group<f_Group>, Flags<[CC1Option]>,
HelpText<"Disable support for int128_t type">;
-
+def fkeep_static_consts : Flag<["-"], "fkeep-static-consts">, Group<f_Group>, Flags<[CC1Option]>,
+ HelpText<"Keep static const variables even if unused">;
def ffixed_point : Flag<["-"], "ffixed-point">, Group<f_Group>,
Flags<[CC1Option]>, HelpText<"Enable fixed point types">;
def fno_fixed_point : Flag<["-"], "fno-fixed-point">, Group<f_Group>,
Modified: cfe/trunk/include/clang/Frontend/CodeGenOptions.def
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Frontend/CodeGenOptions.def?rev=340439&r1=340438&r2=340439&view=diff
==============================================================================
--- cfe/trunk/include/clang/Frontend/CodeGenOptions.def (original)
+++ cfe/trunk/include/clang/Frontend/CodeGenOptions.def Wed Aug 22 12:05:19 2018
@@ -341,6 +341,9 @@ CODEGENOPT(Addrsig, 1, 0)
ENUM_CODEGENOPT(SignReturnAddress, SignReturnAddressScope, 2, None)
+/// Whether to emit unused static constants.
+CODEGENOPT(KeepStaticConsts, 1, 0)
+
#undef CODEGENOPT
#undef ENUM_CODEGENOPT
#undef VALUE_CODEGENOPT
Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=340439&r1=340438&r2=340439&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Wed Aug 22 12:05:19 2018
@@ -1350,6 +1350,12 @@ void CodeGenModule::SetCommonAttributes(
if (D && D->hasAttr<UsedAttr>())
addUsedGlobal(GV);
+
+ if (CodeGenOpts.KeepStaticConsts && D && isa<VarDecl>(D)) {
+ const auto *VD = cast<VarDecl>(D);
+ if (VD->getType().isConstQualified() && VD->getStorageClass() == SC_Static)
+ addUsedGlobal(GV);
+ }
}
bool CodeGenModule::GetCPUAndFeaturesAttributes(const Decl *D,
@@ -1985,6 +1991,13 @@ bool CodeGenModule::MustBeEmitted(const
if (LangOpts.EmitAllDecls)
return true;
+ if (CodeGenOpts.KeepStaticConsts) {
+ const auto *VD = dyn_cast<VarDecl>(Global);
+ if (VD && VD->getType().isConstQualified() &&
+ VD->getStorageClass() == SC_Static)
+ return true;
+ }
+
return getContext().DeclMustBeEmitted(Global);
}
Modified: cfe/trunk/lib/Driver/ToolChains/Clang.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Driver/ToolChains/Clang.cpp?rev=340439&r1=340438&r2=340439&view=diff
==============================================================================
--- cfe/trunk/lib/Driver/ToolChains/Clang.cpp (original)
+++ cfe/trunk/lib/Driver/ToolChains/Clang.cpp Wed Aug 22 12:05:19 2018
@@ -4008,6 +4008,7 @@ void Clang::ConstructJob(Compilation &C,
Args.AddLastArg(CmdArgs, options::OPT_fno_operator_names);
Args.AddLastArg(CmdArgs, options::OPT_femulated_tls,
options::OPT_fno_emulated_tls);
+ Args.AddLastArg(CmdArgs, options::OPT_fkeep_static_consts);
// AltiVec-like language extensions aren't relevant for assembling.
if (!isa<PreprocessJobAction>(JA) || Output.getType() != types::TY_PP_Asm)
Modified: cfe/trunk/lib/Frontend/CompilerInvocation.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Frontend/CompilerInvocation.cpp?rev=340439&r1=340438&r2=340439&view=diff
==============================================================================
--- cfe/trunk/lib/Frontend/CompilerInvocation.cpp (original)
+++ cfe/trunk/lib/Frontend/CompilerInvocation.cpp Wed Aug 22 12:05:19 2018
@@ -1145,6 +1145,8 @@ static bool ParseCodeGenArgs(CodeGenOpti
<< A->getAsString(Args) << A->getValue();
}
+ Opts.KeepStaticConsts = Args.hasArg(OPT_fkeep_static_consts);
+
return Success;
}
Added: cfe/trunk/test/CodeGen/keep-static-consts.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/keep-static-consts.cpp?rev=340439&view=auto
==============================================================================
--- cfe/trunk/test/CodeGen/keep-static-consts.cpp (added)
+++ cfe/trunk/test/CodeGen/keep-static-consts.cpp Wed Aug 22 12:05:19 2018
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -fkeep-static-consts -emit-llvm %s -o - -triple=x86_64-unknown-linux-gnu | FileCheck %s
+
+// CHECK: @_ZL7srcvers = internal constant [4 x i8] c"xyz\00", align 1
+// CHECK: @llvm.used = appending global [1 x i8*] [i8* getelementptr inbounds ([4 x i8], [4 x i8]* @_ZL7srcvers, i32 0, i32 0)], section "llvm.metadata"
+static const char srcvers[] = "xyz";
+extern const int b = 1;
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