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Make -linkonce-templates less aggressive by default & add -linkonce-templates-aggressive #3924

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Feb 28, 2022
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Make -linkonce-templates less aggressive by default & add -linkonce-templates-aggressive #3924

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9 changes: 5 additions & 4 deletions dmd/dsymbolsem.d
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Original file line number Diff line number Diff line change
Expand Up @@ -5890,8 +5890,8 @@ void templateInstanceSemantic(TemplateInstance tempinst, Scope* sc, Expressions*
}

// LDC: the tnext linked list is only used by TemplateInstance.needsCodegen(),
// which is skipped with -linkonce-templates
if (!(IN_LLVM && global.params.linkonceTemplates))
// which is skipped with -linkonce-templates-aggressive
if (!(IN_LLVM && global.params.linkonceTemplates == LinkonceTemplates.aggressive))
{
tempinst.tnext = tempinst.inst.tnext;
tempinst.inst.tnext = tempinst;
Expand Down Expand Up @@ -5979,9 +5979,10 @@ void templateInstanceSemantic(TemplateInstance tempinst, Scope* sc, Expressions*
scope v = new InstMemberWalker(tempinst.inst);
tempinst.inst.accept(v);

if (IN_LLVM && global.params.linkonceTemplates)
if (IN_LLVM && global.params.linkonceTemplates == LinkonceTemplates.aggressive)
{
// with -linkonce-templates, an earlier speculative or non-root instance hasn't been appended to any module yet
// with -linkonce-templates-aggressive, an earlier speculative or non-root instance
// hasn't been appended to any module yet
assert(tempinst.inst.memberOf is null);
tempinst.inst.appendToModuleMember();
}
Expand Down
4 changes: 2 additions & 2 deletions dmd/dtemplate.d
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Expand Up @@ -6241,7 +6241,7 @@ extern (C++) class TemplateInstance : ScopeDsymbol
{
version (IN_LLVM)
{
assert(!global.params.linkonceTemplates);
assert(global.params.linkonceTemplates != LinkonceTemplates.aggressive);
}

// minst is finalized after the 1st invocation.
Expand Down Expand Up @@ -7370,7 +7370,7 @@ version (IN_LLVM)

version (IN_LLVM)
{
if (global.params.linkonceTemplates)
if (global.params.linkonceTemplates == LinkonceTemplates.aggressive)
{
// Skip if it's not a root module.
if (!mi || !mi.isRoot())
Expand Down
11 changes: 10 additions & 1 deletion dmd/globals.d
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Expand Up @@ -116,12 +116,21 @@ enum FeatureState : byte
}

version (IN_LLVM)
{
enum LinkonceTemplates : byte
{
no, // non-discardable weak_odr linkage
yes, // discardable linkonce_odr linkage + lazily and recursively define all referenced instantiated symbols in each object file (define-on-declare)
aggressive // be more aggressive wrt. speculative instantiations - don't append to module members and skip needsCodegen() culling; rely on define-on-declare.
}

enum DLLImport : byte
{
none,
defaultLibsOnly, // only symbols from druntime/Phobos
all
}
} // IN_LLVM

/// Put command line switches in here
extern (C++) struct Param
Expand Down Expand Up @@ -316,7 +325,7 @@ version (IN_LLVM)

bool outputSourceLocations; // if true, output line tables.

bool linkonceTemplates; // -linkonce-templates
LinkonceTemplates linkonceTemplates; // -linkonce-templates

// Windows-specific:
bool dllexport; // dllexport ~all defined symbols?
Expand Down
9 changes: 8 additions & 1 deletion dmd/globals.h
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Expand Up @@ -99,6 +99,13 @@ enum class FeatureState : signed char
};

#if IN_LLVM
enum class LinkonceTemplates : char
{
no, // non-discardable weak_odr linkage
yes, // discardable linkonce_odr linkage + lazily and recursively define all referenced instantiated symbols in each object file (define-on-declare)
aggressive // be more aggressive wrt. speculative instantiations - don't append to module members and skip needsCodegen() culling; rely on define-on-declare.
};

enum class DLLImport : char
{
none,
Expand Down Expand Up @@ -286,7 +293,7 @@ struct Param

bool outputSourceLocations; // if true, output line tables.

bool linkonceTemplates; // -linkonce-templates
LinkonceTemplates linkonceTemplates; // -linkonce-templates

// Windows-specific:
bool dllexport; // dllexport ~all defined symbols?
Expand Down
15 changes: 10 additions & 5 deletions driver/cl_options.cpp
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Expand Up @@ -515,11 +515,16 @@ cl::opt<uint32_t, true> hashThreshold(
"hash-threshold", cl::ZeroOrMore, cl::location(global.params.hashThreshold),
cl::desc("Hash symbol names longer than this threshold (experimental)"));

static cl::opt<bool, true> linkonceTemplates(
"linkonce-templates", cl::ZeroOrMore,
cl::location(global.params.linkonceTemplates),
cl::desc(
"Use linkonce_odr linkage for template symbols instead of weak_odr"));
static cl::opt<LinkonceTemplates, true> linkonceTemplates(
cl::ZeroOrMore, cl::location(global.params.linkonceTemplates),
cl::values(
clEnumValN(LinkonceTemplates::yes, "linkonce-templates",
"Use discardable linkonce_odr linkage for template symbols "
"and lazily & recursively define all referenced "
"instantiated symbols in each object file"),
clEnumValN(LinkonceTemplates::aggressive,
"linkonce-templates-aggressive",
"Experimental, more aggressive variant")));

cl::opt<bool> disableLinkerStripDead(
"disable-linker-strip-dead", cl::ZeroOrMore,
Expand Down
6 changes: 3 additions & 3 deletions driver/main.cpp
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Expand Up @@ -449,9 +449,9 @@ void parseCommandLine(Strings &sourceFiles) {
global.params.output_mlir = opts::output_mlir ? OUTPUTFLAGset : OUTPUTFLAGno;
global.params.output_s = opts::output_s ? OUTPUTFLAGset : OUTPUTFLAGno;

templateLinkage = global.params.linkonceTemplates
? LLGlobalValue::LinkOnceODRLinkage
: LLGlobalValue::WeakODRLinkage;
templateLinkage = global.params.linkonceTemplates == LinkonceTemplates::no
? LLGlobalValue::WeakODRLinkage
: LLGlobalValue::LinkOnceODRLinkage;

if (global.params.run || !runargs.empty()) {
// FIXME: how to properly detect the presence of a PositionalEatsArgs
Expand Down
14 changes: 8 additions & 6 deletions gen/declarations.cpp
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Expand Up @@ -319,13 +319,15 @@ class CodegenVisitor : public Visitor {
return;
}

// With -linkonce-templates, only non-speculative instances make it to
// module members (see `TemplateInstance.appendToModuleMember()`), and we
// don't need full needsCodegen() culling in that case; isDiscardable() is
// sufficient. Speculative ones are lazily emitted if actually referenced
// With -linkonce-templates-aggressive, only non-speculative instances make
// it to module members (see `TemplateInstance.appendToModuleMember()`), and
// we don't need full needsCodegen() culling in that case; isDiscardable()
// is sufficient. Speculative ones are lazily emitted if actually referenced
// during codegen - per IR module.
if ((global.params.linkonceTemplates && decl->isDiscardable()) ||
(!global.params.linkonceTemplates && !decl->needsCodegen())) {
if ((global.params.linkonceTemplates == LinkonceTemplates::aggressive &&
decl->isDiscardable()) ||
(global.params.linkonceTemplates != LinkonceTemplates::aggressive &&
!decl->needsCodegen())) {
Logger::println("Does not need codegen, skipping.");
return;
}
Expand Down
7 changes: 4 additions & 3 deletions gen/llvmhelpers.cpp
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Expand Up @@ -1733,8 +1733,9 @@ static bool isDefaultLibSymbol(Dsymbol *sym) {
(md->packages.length > 1 && md->packages.ptr[1] == Id::io)));
}

bool defineOnDeclare(Dsymbol* sym, bool) {
return global.params.linkonceTemplates && sym->isInstantiated();
bool defineOnDeclare(Dsymbol *sym, bool) {
return global.params.linkonceTemplates != LinkonceTemplates::no &&
sym->isInstantiated();
}

bool dllimportDataSymbol(Dsymbol *sym) {
Expand All @@ -1750,7 +1751,7 @@ bool dllimportDataSymbol(Dsymbol *sym) {
return !mod->isRoot(); // non-root ModuleInfo symbol
} else if (sym->inNonRoot()) {
return true; // not instantiated, and defined in non-root
} else if (!global.params.linkonceTemplates &&
} else if (global.params.linkonceTemplates == LinkonceTemplates::no &&
sym->isInstantiated()) {
return true; // instantiated but potentially culled (needsCodegen())
} else if (auto vd = sym->isVarDeclaration()) {
Expand Down