[PATCH] D40925: Add option -fkeep-static-consts

[Elizabeth Andrews via Phabricator via cfe-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rC340439: Currently clang does not emit unused static constants. GCC emits these (authored by eandrews, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D40925?vs=161544&id=162022#toc

Repository:
  rC Clang

https://reviews.llvm.org/D40925

Files:
  include/clang/Driver/Options.td
  include/clang/Frontend/CodeGenOptions.def
  lib/CodeGen/CodeGenModule.cpp
  lib/Driver/ToolChains/Clang.cpp
  lib/Frontend/CompilerInvocation.cpp
  test/CodeGen/keep-static-consts.cpp


Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -893,7 +893,8 @@
 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>,
Index: include/clang/Frontend/CodeGenOptions.def
===================================================================
--- include/clang/Frontend/CodeGenOptions.def
+++ include/clang/Frontend/CodeGenOptions.def
@@ -341,6 +341,9 @@
 
 ENUM_CODEGENOPT(SignReturnAddress, SignReturnAddressScope, 2, None)
 
+/// Whether to emit unused static constants.
+CODEGENOPT(KeepStaticConsts, 1, 0)
+
 #undef CODEGENOPT
 #undef ENUM_CODEGENOPT
 #undef VALUE_CODEGENOPT
Index: test/CodeGen/keep-static-consts.cpp
===================================================================
--- test/CodeGen/keep-static-consts.cpp
+++ test/CodeGen/keep-static-consts.cpp
@@ -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;
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -1145,6 +1145,8 @@
           << A->getAsString(Args) << A->getValue();
   }
 
+  Opts.KeepStaticConsts = Args.hasArg(OPT_fkeep_static_consts);
+
   return Success;
 }
 
Index: lib/CodeGen/CodeGenModule.cpp
===================================================================
--- lib/CodeGen/CodeGenModule.cpp
+++ lib/CodeGen/CodeGenModule.cpp
@@ -1350,6 +1350,12 @@
 
   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 @@
   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);
 }
 
Index: lib/Driver/ToolChains/Clang.cpp
===================================================================
--- lib/Driver/ToolChains/Clang.cpp
+++ lib/Driver/ToolChains/Clang.cpp
@@ -4008,6 +4008,7 @@
   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)


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