Support the Nodebug emission kind for DICompileUnits.

Sample-based profiling and optimization remarks currently remove
DICompileUnits from llvm.dbg.cu to suppress the emission of debug info
from them. This is somewhat of a hack and only borderline legal IR.

This patch uses the recently introduced NoDebug emission kind in
DICompileUnit to achieve the same result without breaking the Verifier.
A nice side-effect of this change is that it is now possible to combine
NoDebug and regular compile units under LTO.

http://reviews.llvm.org/D18808
<rdar://problem/25427165>

llvm-svn: 265861

1 files changed, 21 insertions, 12 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 296a799d33c..d9d265ef2b9 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -466,15 +466,18 @@ void DwarfDebug::beginModule() {
 
   const Module *M = MMI->getModule();
 
-  NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu");
-  if (!CU_Nodes)
-    return;
-  TypeIdentifierMap = generateDITypeIdentifierMap(CU_Nodes);
+  TypeIdentifierMap = generateDITypeIdentifierMap(*M);
+  unsigned NumDebugCUs = 0;
+  for (DICompileUnit *CUNode : M->debug_compile_units()) {
+    (void)CUNode;
+    ++NumDebugCUs;
+  }
 
-  SingleCU = CU_Nodes->getNumOperands() == 1;
+  // Tell MMI whether we have debug info.
+  MMI->setDebugInfoAvailability(NumDebugCUs > 0);
+  SingleCU = NumDebugCUs == 1;
 
-  for (MDNode *N : CU_Nodes->operands()) {
-    auto *CUNode = cast<DICompileUnit>(N);
+  for (DICompileUnit *CUNode : M->debug_compile_units()) {
     DwarfCompileUnit &CU = constructDwarfCompileUnit(CUNode);
     for (auto *IE : CUNode->getImportedEntities())
       CU.addImportedEntity(IE);
@@ -500,9 +503,6 @@ void DwarfDebug::beginModule() {
     for (auto *IE : CUNode->getImportedEntities())
       constructAndAddImportedEntityDIE(CU, IE);
   }
-
-  // Tell MMI that we have debug info.
-  MMI->setDebugInfoAvailability(true);
 }
 
 void DwarfDebug::finishVariableDefinitions() {
@@ -538,6 +538,9 @@ void DwarfDebug::collectDeadVariables() {
   if (NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu")) {
     for (MDNode *N : CU_Nodes->operands()) {
       auto *TheCU = cast<DICompileUnit>(N);
+      if (TheCU->getEmissionKind() == DICompileUnit::NoDebug)
+        continue;
+
       // Construct subprogram DIE and add variables DIEs.
       DwarfCompileUnit *SPCU =
           static_cast<DwarfCompileUnit *>(CUMap.lookup(TheCU));
@@ -1090,7 +1093,10 @@ void DwarfDebug::beginFunction(const MachineFunction *MF) {
   // includes the directory of the cpp file being built, even when the file name
   // is absolute (such as an <> lookup header)))
   DwarfCompileUnit *TheCU = SPMap.lookup(FnScope->getScopeNode());
-  assert(TheCU && "Unable to find compile unit!");
+  if (!TheCU)
+    // Once DISubprogram points to the owning CU, we can assert that the CU has
+    // a NoDebug EmissionKind here.
+    return;
   if (Asm->OutStreamer->hasRawTextSupport())
     // Use a single line table if we are generating assembly.
     Asm->OutStreamer->getContext().setDwarfCompileUnitID(0);
@@ -1113,7 +1119,10 @@ void DwarfDebug::endFunction(const MachineFunction *MF) {
       "endFunction should be called with the same function as beginFunction");
 
   if (!MMI->hasDebugInfo() || LScopes.empty() ||
-      !MF->getFunction()->getSubprogram()) {
+      !MF->getFunction()->getSubprogram() ||
+      // Once DISubprogram points to the owning CU, we can check for a
+      // CU with a NoDebug EmissionKind here.
+      !SPMap.lookup(MF->getFunction()->getSubprogram())) {
     // If we don't have a lexical scope for this function then there will
     // be a hole in the range information. Keep note of this by setting the
     // previously used section to nullptr.