DebugInfo: Do not emit empty CUs
Consistent with GCC and addresses a shortcoming with ThinLTO where many
imported CUs may end up being empty (because the functions imported from
them either ended up not being used (and were then discarded, since
they're imported as available_externally) or optimized away entirely).
Test cases previously testing empty CUs (either intentionally, or
because they didn't need anything more complicated) had a trivial 'int'
or similar basic type added to their retained types list.
This is a first order approximation - a deeper implementation could do
things like:
1) Be more lazy about construction of the CU - for example if two CUs
containing a single identical retained type are linked together, with
this change one of the two CUs will be produced but empty (since a
duplicate type won't be produced).
2) Go further and invert all the CU links the same way the subprogram
link is inverted - keep named CU lists of retained types, macros, etc,
and have those link back to the CU. Then if they're emitted, the CU is
emitted, but never otherwise - this would allow the metadata itself to
be dropped earlier too, though it seems unlikely that's an important
optimization as there shouldn't be many CUs relative to the number of
other entities.
llvm-svn: 304020
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 3ea4c1c..b6cd82a 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -374,7 +374,7 @@
// Find the subprogram's DwarfCompileUnit in the SPMap in case the subprogram
// was inlined from another compile unit.
- auto &CU = *CUMap.lookup(SP->getUnit());
+ auto &CU = getOrCreateDwarfCompileUnit(SP->getUnit());
if (auto *SkelCU = CU.getSkeleton()) {
(shareAcrossDWOCUs() ? CU : SrcCU)
.constructAbstractSubprogramScopeDIE(Scope);
@@ -407,7 +407,9 @@
// Create new DwarfCompileUnit for the given metadata node with tag
// DW_TAG_compile_unit.
DwarfCompileUnit &
-DwarfDebug::constructDwarfCompileUnit(const DICompileUnit *DIUnit) {
+DwarfDebug::getOrCreateDwarfCompileUnit(const DICompileUnit *DIUnit) {
+ if (auto *CU = CUMap.lookup(DIUnit))
+ return *CU;
StringRef FN = DIUnit->getFilename();
CompilationDir = DIUnit->getDirectory();
@@ -540,7 +542,12 @@
}
for (DICompileUnit *CUNode : M->debug_compile_units()) {
- DwarfCompileUnit &CU = constructDwarfCompileUnit(CUNode);
+ if (CUNode->getEnumTypes().empty() && CUNode->getRetainedTypes().empty() &&
+ CUNode->getGlobalVariables().empty() &&
+ CUNode->getImportedEntities().empty() && CUNode->getMacros().empty())
+ continue;
+
+ DwarfCompileUnit &CU = getOrCreateDwarfCompileUnit(CUNode);
for (auto *IE : CUNode->getImportedEntities())
CU.addImportedEntity(IE);
@@ -587,11 +594,12 @@
}
void DwarfDebug::finishSubprogramDefinitions() {
- for (const DISubprogram *SP : ProcessedSPNodes)
- if (SP->getUnit()->getEmissionKind() != DICompileUnit::NoDebug)
- forBothCUs(*CUMap.lookup(SP->getUnit()), [&](DwarfCompileUnit &CU) {
- CU.finishSubprogramDefinition(SP);
- });
+ for (const DISubprogram *SP : ProcessedSPNodes) {
+ assert(SP->getUnit()->getEmissionKind() != DICompileUnit::NoDebug);
+ forBothCUs(
+ getOrCreateDwarfCompileUnit(SP->getUnit()),
+ [&](DwarfCompileUnit &CU) { CU.finishSubprogramDefinition(SP); });
+ }
}
void DwarfDebug::finalizeModuleInfo() {
@@ -1136,12 +1144,10 @@
auto *SP = MF->getFunction()->getSubprogram();
assert(LScopes.empty() || SP == LScopes.getCurrentFunctionScope()->getScopeNode());
- DwarfCompileUnit *TheCU = CUMap.lookup(SP->getUnit());
- if (!TheCU) {
- assert(SP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug &&
- "DICompileUnit missing from llvm.dbg.cu?");
+ if (SP->getUnit()->getEmissionKind() == DICompileUnit::NoDebug)
return;
- }
+
+ DwarfCompileUnit &CU = getOrCreateDwarfCompileUnit(SP->getUnit());
// Set DwarfDwarfCompileUnitID in MCContext to the Compile Unit this function
// belongs to so that we add to the correct per-cu line table in the
@@ -1150,7 +1156,7 @@
// Use a single line table if we are generating assembly.
Asm->OutStreamer->getContext().setDwarfCompileUnitID(0);
else
- Asm->OutStreamer->getContext().setDwarfCompileUnitID(TheCU->getUniqueID());
+ Asm->OutStreamer->getContext().setDwarfCompileUnitID(CU.getUniqueID());
// Record beginning of function.
PrologEndLoc = findPrologueEndLoc(MF);
@@ -1546,6 +1552,9 @@
// Emit locations into the debug loc section.
void DwarfDebug::emitDebugLoc() {
+ if (DebugLocs.getLists().empty())
+ return;
+
// Start the dwarf loc section.
Asm->OutStreamer->SwitchSection(
Asm->getObjFileLowering().getDwarfLocSection());
@@ -1757,6 +1766,9 @@
/// Emit address ranges into a debug ranges section.
void DwarfDebug::emitDebugRanges() {
+ if (CUMap.empty())
+ return;
+
// Start the dwarf ranges section.
Asm->OutStreamer->SwitchSection(
Asm->getObjFileLowering().getDwarfRangesSection());
@@ -1836,6 +1848,9 @@
/// Emit macros into a debug macinfo section.
void DwarfDebug::emitDebugMacinfo() {
+ if (CUMap.empty())
+ return;
+
// Start the dwarf macinfo section.
Asm->OutStreamer->SwitchSection(
Asm->getObjFileLowering().getDwarfMacinfoSection());
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
index 97b96dd..ebfba4c 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -416,7 +416,7 @@
/// Create new DwarfCompileUnit for the given metadata node with tag
/// DW_TAG_compile_unit.
- DwarfCompileUnit &constructDwarfCompileUnit(const DICompileUnit *DIUnit);
+ DwarfCompileUnit &getOrCreateDwarfCompileUnit(const DICompileUnit *DIUnit);
/// Construct imported_module or imported_declaration DIE.
void constructAndAddImportedEntityDIE(DwarfCompileUnit &TheCU,