r219960 - MS Compat: mark globals emitted in read-only sections const
Hans Wennborg
hans at hanshq.net
Thu Oct 16 13:52:46 PDT 2014
Author: hans
Date: Thu Oct 16 15:52:46 2014
New Revision: 219960
URL: http://llvm.org/viewvc/llvm-project?rev=219960&view=rev
Log:
MS Compat: mark globals emitted in read-only sections const
They cannot be written to, so marking them const makes sense and may improve
optimisation.
As a side-effect, SectionInfos has to be moved from Sema to ASTContext.
It also fixes this problem, that occurs when compiling ATL:
warning LNK4254: section 'ATL' (C0000040) merged into '.rdata' (40000040) with different attributes
The ATL headers are putting variables in a special section that's marked
read-only. However, Clang currently can't model that read-onlyness in the IR.
But, by making the variables const, the section does become read-only, and
the linker warning is avoided.
Differential Revision: http://reviews.llvm.org/D5812
Modified:
cfe/trunk/include/clang/AST/ASTContext.h
cfe/trunk/include/clang/Sema/Sema.h
cfe/trunk/lib/CodeGen/CodeGenModule.cpp
cfe/trunk/lib/Parse/ParsePragma.cpp
cfe/trunk/lib/Sema/SemaAttr.cpp
cfe/trunk/lib/Sema/SemaDecl.cpp
cfe/trunk/test/CodeGen/sections.c
Modified: cfe/trunk/include/clang/AST/ASTContext.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/ASTContext.h?rev=219960&r1=219959&r2=219960&view=diff
==============================================================================
--- cfe/trunk/include/clang/AST/ASTContext.h (original)
+++ cfe/trunk/include/clang/AST/ASTContext.h Thu Oct 16 15:52:46 2014
@@ -2328,6 +2328,31 @@ private:
std::unique_ptr<ParentMap> AllParents;
std::unique_ptr<VTableContextBase> VTContext;
+
+public:
+ enum PragmaSectionFlag : unsigned {
+ PSF_None = 0,
+ PSF_Read = 0x1,
+ PSF_Write = 0x2,
+ PSF_Execute = 0x4,
+ PSF_Implicit = 0x8,
+ PSF_Invalid = 0x80000000U,
+ };
+
+ struct SectionInfo {
+ DeclaratorDecl *Decl;
+ SourceLocation PragmaSectionLocation;
+ int SectionFlags;
+ SectionInfo() {}
+ SectionInfo(DeclaratorDecl *Decl,
+ SourceLocation PragmaSectionLocation,
+ int SectionFlags)
+ : Decl(Decl),
+ PragmaSectionLocation(PragmaSectionLocation),
+ SectionFlags(SectionFlags) {}
+ };
+
+ llvm::StringMap<SectionInfo> SectionInfos;
};
/// \brief Utility function for constructing a nullary selector.
Modified: cfe/trunk/include/clang/Sema/Sema.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Sema.h?rev=219960&r1=219959&r2=219960&view=diff
==============================================================================
--- cfe/trunk/include/clang/Sema/Sema.h (original)
+++ cfe/trunk/include/clang/Sema/Sema.h Thu Oct 16 15:52:46 2014
@@ -7218,29 +7218,6 @@ public:
PSK_CodeSeg,
};
- enum PragmaSectionFlag : unsigned {
- PSF_None = 0,
- PSF_Read = 0x1,
- PSF_Write = 0x2,
- PSF_Execute = 0x4,
- PSF_Implicit = 0x8,
- PSF_Invalid = 0x80000000U,
- };
-
- struct SectionInfo {
- DeclaratorDecl *Decl;
- SourceLocation PragmaSectionLocation;
- int SectionFlags;
- SectionInfo() {}
- SectionInfo(DeclaratorDecl *Decl,
- SourceLocation PragmaSectionLocation,
- int SectionFlags)
- : Decl(Decl),
- PragmaSectionLocation(PragmaSectionLocation),
- SectionFlags(SectionFlags) {}
- };
-
- llvm::StringMap<SectionInfo> SectionInfos;
bool UnifySection(StringRef SectionName,
int SectionFlags,
DeclaratorDecl *TheDecl);
Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=219960&r1=219959&r2=219960&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Thu Oct 16 15:52:46 2014
@@ -1931,6 +1931,13 @@ void CodeGenModule::EmitGlobalVarDefinit
GV->setConstant(!NeedsGlobalCtor && !NeedsGlobalDtor &&
isTypeConstant(D->getType(), true));
+ // If it is in a read-only section, mark it 'constant'.
+ if (const SectionAttr *SA = D->getAttr<SectionAttr>()) {
+ const ASTContext::SectionInfo &SI = Context.SectionInfos[SA->getName()];
+ if ((SI.SectionFlags & ASTContext::PSF_Write) == 0)
+ GV->setConstant(true);
+ }
+
GV->setAlignment(getContext().getDeclAlign(D).getQuantity());
// Set the llvm linkage type as appropriate.
Modified: cfe/trunk/lib/Parse/ParsePragma.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Parse/ParsePragma.cpp?rev=219960&r1=219959&r2=219960&view=diff
==============================================================================
--- cfe/trunk/lib/Parse/ParsePragma.cpp (original)
+++ cfe/trunk/lib/Parse/ParsePragma.cpp Thu Oct 16 15:52:46 2014
@@ -12,6 +12,7 @@
//===----------------------------------------------------------------------===//
#include "RAIIObjectsForParser.h"
+#include "clang/AST/ASTContext.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Parse/ParseDiagnostic.h"
@@ -539,20 +540,20 @@ bool Parser::HandlePragmaMSSection(Strin
<< PragmaName;
return false;
}
- Sema::PragmaSectionFlag Flag =
- llvm::StringSwitch<Sema::PragmaSectionFlag>(
+ ASTContext::PragmaSectionFlag Flag =
+ llvm::StringSwitch<ASTContext::PragmaSectionFlag>(
Tok.getIdentifierInfo()->getName())
- .Case("read", Sema::PSF_Read)
- .Case("write", Sema::PSF_Write)
- .Case("execute", Sema::PSF_Execute)
- .Case("shared", Sema::PSF_Invalid)
- .Case("nopage", Sema::PSF_Invalid)
- .Case("nocache", Sema::PSF_Invalid)
- .Case("discard", Sema::PSF_Invalid)
- .Case("remove", Sema::PSF_Invalid)
- .Default(Sema::PSF_None);
- if (Flag == Sema::PSF_None || Flag == Sema::PSF_Invalid) {
- PP.Diag(PragmaLocation, Flag == Sema::PSF_None
+ .Case("read", ASTContext::PSF_Read)
+ .Case("write", ASTContext::PSF_Write)
+ .Case("execute", ASTContext::PSF_Execute)
+ .Case("shared", ASTContext::PSF_Invalid)
+ .Case("nopage", ASTContext::PSF_Invalid)
+ .Case("nocache", ASTContext::PSF_Invalid)
+ .Case("discard", ASTContext::PSF_Invalid)
+ .Case("remove", ASTContext::PSF_Invalid)
+ .Default(ASTContext::PSF_None);
+ if (Flag == ASTContext::PSF_None || Flag == ASTContext::PSF_Invalid) {
+ PP.Diag(PragmaLocation, Flag == ASTContext::PSF_None
? diag::warn_pragma_invalid_specific_action
: diag::warn_pragma_unsupported_action)
<< PragmaName << Tok.getIdentifierInfo()->getName();
Modified: cfe/trunk/lib/Sema/SemaAttr.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaAttr.cpp?rev=219960&r1=219959&r2=219960&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaAttr.cpp (original)
+++ cfe/trunk/lib/Sema/SemaAttr.cpp Thu Oct 16 15:52:46 2014
@@ -363,15 +363,15 @@ void Sema::PragmaStack<ValueType>::Act(S
bool Sema::UnifySection(StringRef SectionName,
int SectionFlags,
DeclaratorDecl *Decl) {
- auto Section = SectionInfos.find(SectionName);
- if (Section == SectionInfos.end()) {
- SectionInfos[SectionName] =
- SectionInfo(Decl, SourceLocation(), SectionFlags);
+ auto Section = Context.SectionInfos.find(SectionName);
+ if (Section == Context.SectionInfos.end()) {
+ Context.SectionInfos[SectionName] =
+ ASTContext::SectionInfo(Decl, SourceLocation(), SectionFlags);
return false;
}
// A pre-declared section takes precedence w/o diagnostic.
if (Section->second.SectionFlags == SectionFlags ||
- !(Section->second.SectionFlags & PSF_Implicit))
+ !(Section->second.SectionFlags & ASTContext::PSF_Implicit))
return false;
auto OtherDecl = Section->second.Decl;
Diag(Decl->getLocation(), diag::err_section_conflict)
@@ -390,11 +390,11 @@ bool Sema::UnifySection(StringRef Sectio
bool Sema::UnifySection(StringRef SectionName,
int SectionFlags,
SourceLocation PragmaSectionLocation) {
- auto Section = SectionInfos.find(SectionName);
- if (Section != SectionInfos.end()) {
+ auto Section = Context.SectionInfos.find(SectionName);
+ if (Section != Context.SectionInfos.end()) {
if (Section->second.SectionFlags == SectionFlags)
return false;
- if (!(Section->second.SectionFlags & PSF_Implicit)) {
+ if (!(Section->second.SectionFlags & ASTContext::PSF_Implicit)) {
Diag(PragmaSectionLocation, diag::err_section_conflict)
<< "this" << "a prior #pragma section";
Diag(Section->second.PragmaSectionLocation,
@@ -402,8 +402,8 @@ bool Sema::UnifySection(StringRef Sectio
return true;
}
}
- SectionInfos[SectionName] =
- SectionInfo(nullptr, PragmaSectionLocation, SectionFlags);
+ Context.SectionInfos[SectionName] =
+ ASTContext::SectionInfo(nullptr, PragmaSectionLocation, SectionFlags);
return false;
}
Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=219960&r1=219959&r2=219960&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDecl.cpp Thu Oct 16 15:52:46 2014
@@ -7334,7 +7334,9 @@ Sema::ActOnFunctionDeclarator(Scope *S,
CodeSegStack.CurrentValue->getString(),
CodeSegStack.CurrentPragmaLocation));
if (UnifySection(CodeSegStack.CurrentValue->getString(),
- PSF_Implicit | PSF_Execute | PSF_Read, NewFD))
+ ASTContext::PSF_Implicit | ASTContext::PSF_Execute |
+ ASTContext::PSF_Read,
+ NewFD))
NewFD->dropAttr<SectionAttr>();
}
@@ -9403,15 +9405,15 @@ void Sema::CheckCompleteVariableDeclarat
if (var->isThisDeclarationADefinition() &&
ActiveTemplateInstantiations.empty()) {
PragmaStack<StringLiteral *> *Stack = nullptr;
- int SectionFlags = PSF_Implicit | PSF_Read;
+ int SectionFlags = ASTContext::PSF_Implicit | ASTContext::PSF_Read;
if (var->getType().isConstQualified())
Stack = &ConstSegStack;
else if (!var->getInit()) {
Stack = &BSSSegStack;
- SectionFlags |= PSF_Write;
+ SectionFlags |= ASTContext::PSF_Write;
} else {
Stack = &DataSegStack;
- SectionFlags |= PSF_Write;
+ SectionFlags |= ASTContext::PSF_Write;
}
if (!var->hasAttr<SectionAttr>() && Stack->CurrentValue)
var->addAttr(
Modified: cfe/trunk/test/CodeGen/sections.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/sections.c?rev=219960&r1=219959&r2=219960&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/sections.c (original)
+++ cfe/trunk/test/CodeGen/sections.c Thu Oct 16 15:52:46 2014
@@ -31,6 +31,14 @@ int i;
int TEST1;
#pragma bss_seg(pop)
int TEST2;
+
+#pragma section("read_flag_section", read)
+// Even though they are not declared const, these become constant since they are
+// in a read-only section.
+__declspec(allocate("read_flag_section")) int unreferenced = 0;
+extern __declspec(allocate("read_flag_section")) int referenced = 42;
+int *user() { return &referenced; }
+
#ifdef __cplusplus
}
#endif
@@ -47,5 +55,7 @@ int TEST2;
//CHECK: @i = global i32 0
//CHECK: @TEST1 = global i32 0
//CHECK: @TEST2 = global i32 0, section ".bss1"
+//CHECK: @unreferenced = constant i32 0, section "read_flag_section"
+//CHECK: @referenced = constant i32 42, section "read_flag_section"
//CHECK: define void @g()
//CHECK: define void @h() {{.*}} section ".my_code"
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