[StripDeadDebug/DIFinder] Track inlined SPs

[loladiro]

Summary

In rL299692 I improved strip-dead-debug-info's ability to drop CUs that are not
referenced from the current module. However, in doing so I neglected to realize
that some SPs could be referenced entirely from inlined functions. It appears
I was not the only one to make this mistake, because DebugInfoFinder, doesn't
find those SPs either. Fix this in DebugInfoFinder and then use that to make
sure not to drop those CUs in strip-dead-debug-info.

[loladiro]

Updated to include the test for DIFinder

lib/IR/DebugInfo.cpp

for (auto *Import : CU->getImportedEntities()) {
       else if (auto *SP = dyn_cast<DISubprogram>(Entity))
         processSubprogram(SP);
       else if (auto *NS = dyn_cast<DINamespace>(Entity))
         processScope(NS->getScope());
       else if (auto *M = dyn_cast<DIModule>(Entity))
         processScope(M->getScope());
     }
   }
-  for (auto &F : M.functions())
+  for (auto &F : M.functions()) {
     if (auto *SP = cast_or_null<DISubprogram>(F.getSubprogram()))
       processSubprogram(SP);
+    // There could be subprograms from inlined functions referenced from
+    // instructions only. Walk the function to find them.
+    for (const BasicBlock &BB : F) {
+      for (const Instruction &I : BB) {
+        if (!I.getDebugLoc())
+          continue;
+        processLocation(M, I.getDebugLoc().get());
+      }
+    }
+  }
 }
 
 void DebugInfoFinder::processLocation(const Module &M, const DILocation *Loc) {
   if (!Loc)
     return;
   processScope(Loc->getScope());
   processLocation(M, Loc->getInlinedAt());
 }

lib/Transforms/IPO/StripSymbols.cpp

bool StripDeadDebugInfo::runOnModule(Module &M) {
   for (GlobalVariable &GV : M.globals()) {
     SmallVector<DIGlobalVariableExpression *, 1> GVEs;
     GV.getDebugInfo(GVEs);
     for (auto *GVE : GVEs)
       LiveGVs.insert(GVE);
   }
 
   std::set<DICompileUnit *> LiveCUs;
-  // Any CU referenced from a function is live.
-  for (Function &F : M.functions()) {
-    DISubprogram *SP = F.getSubprogram();
-    if (SP && SP->getUnit())
+  // Any CU referenced from a subprogram is live.
+  for (DISubprogram *SP : F.subprograms()) {
+    if (SP->getUnit())
       LiveCUs.insert(SP->getUnit());
   }
 
   bool HasDeadCUs = false;
   for (DICompileUnit *DIC : F.compile_units()) {
     // Create our live global variable list.
     bool GlobalVariableChange = false;
     for (auto *DIG : DIC->getGlobalVariables()) {

test/Transforms/StripSymbols/strip-dead-debug-info.ll

 entry:
   ret i32 0, !dbg !13
 }
 
 ; Function Attrs: nounwind readonly ssp
 define i32 @foo(i32 %i) #2 !dbg !15 {
 entry:
   tail call void @llvm.dbg.value(metadata i32 %i, i64 0, metadata !18, metadata !19), !dbg !20
-  %.0 = load i32, i32* @xyz, align 4
+  %.0 = load i32, i32* @xyz, align 4, !dbg !30
   ret i32 %.0, !dbg !21
 }
 
 attributes #0 = { nounwind readnone }
 attributes #1 = { nounwind readnone ssp }
 attributes #2 = { nounwind readonly ssp }
 
-!llvm.dbg.cu = !{!4, !23, !24}
+!llvm.dbg.cu = !{!4, !23, !24, !28}
 !llvm.module.flags = !{!9}
 
 !0 = !DIGlobalVariableExpression(var: !1)
 !1 = !DIGlobalVariable(name: "xyz", scope: !2, file: !2, line: 3, type: !3, isLocal: false, isDefinition: true)
 !2 = !DIFile(filename: "g.c", directory: "/tmp/")
 !3 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
 !4 = distinct !DICompileUnit(language: DW_LANG_C89, file: !2, producer: "4.2.1 (Based on Apple Inc. build 5658) (LLVM build)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !5, retainedTypes: !5, globals: !6)
 !5 = !{}

 !20 = !DILocation(line: 7, scope: !15)
 !21 = !DILocation(line: 10, scope: !22)
 !22 = distinct !DILexicalBlock(scope: !15, file: !2, line: 7)
 !23 = distinct !DICompileUnit(language: DW_LANG_C89, file: !2, producer: "GCC", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !5, retainedTypes: !5, globals: !5)
 !24 = distinct !DICompileUnit(language: DW_LANG_C89, file: !2, producer: "Globals", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !5, retainedTypes: !5, globals: !25)
 !25 = !{!26}
 !26 = !DIGlobalVariableExpression(var: !27, expr: !DIExpression(DW_OP_constu, 0, DW_OP_stack_value))
 !27 = !DIGlobalVariable(name: "abcd2", scope: !2, file: !2, line: 2, type: !3, isLocal: true, isDefinition: true)
+!28 = distinct !DICompileUnit(language: DW_LANG_C89, file: !2, producer: "InlineTest", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !5, retainedTypes: !5, globals: !5)
+!29 = distinct !DISubprogram(name: "inlinefunc", linkageName: "inlinefunc", scope: null, file: !2, line: 7, type: !16, isLocal: false, isDefinition: true, isOptimized: true, unit: !28)
+!30 = !DILocation(line: 100, scope: !29, inlinedAt: !21)