Debugging infomration is encoded in llvm IR using metadata. This is designed

such a way that debug info for symbols preserved even if symbols are
optimized away by the optimizer. 

Add new special pass to remove debug info for such symbols.

llvm-svn: 107416

4 files changed, 154 insertions, 0 deletions

diff --git a/llvm/include/llvm/LinkAllPasses.h b/llvm/include/llvm/LinkAllPasses.h
index c2375eaab11..876703b9032 100644
--- a/llvm/include/llvm/LinkAllPasses.h
+++ b/llvm/include/llvm/LinkAllPasses.h
@@ -113,6 +113,7 @@ namespace {
       (void) llvm::createSingleLoopExtractorPass();
       (void) llvm::createStripSymbolsPass();
       (void) llvm::createStripNonDebugSymbolsPass();
+      (void) llvm::createStripDeadDebugInfoPass();
       (void) llvm::createStripDeadPrototypesPass();
       (void) llvm::createTailCallEliminationPass();
       (void) llvm::createTailDuplicationPass();
diff --git a/llvm/include/llvm/Transforms/IPO.h b/llvm/include/llvm/Transforms/IPO.h
index 5e179044229..8fb4b63c646 100644
--- a/llvm/include/llvm/Transforms/IPO.h
+++ b/llvm/include/llvm/Transforms/IPO.h
@@ -45,6 +45,11 @@ ModulePass *createStripNonDebugSymbolsPass();
 ModulePass *createStripDebugDeclarePass();
 
 //===----------------------------------------------------------------------===//
+//
+// These pass removes unused symbols' debug info.
+ModulePass *createStripDeadDebugInfoPass();
+
+//===----------------------------------------------------------------------===//
 /// createLowerSetJmpPass - This function lowers the setjmp/longjmp intrinsics
 /// to invoke/unwind instructions.  This should really be part of the C/C++
 /// front-end, but it's so much easier to write transformations in LLVM proper.
diff --git a/llvm/lib/Transforms/IPO/StripSymbols.cpp b/llvm/lib/Transforms/IPO/StripSymbols.cpp
index 08ad4de429a..12e8db8b4a5 100644
--- a/llvm/lib/Transforms/IPO/StripSymbols.cpp
+++ b/llvm/lib/Transforms/IPO/StripSymbols.cpp
@@ -73,6 +73,19 @@ namespace {
       AU.setPreservesAll();
     }
   };
+
+  class StripDeadDebugInfo : public ModulePass {
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    explicit StripDeadDebugInfo()
+      : ModulePass(&ID) {}
+
+    virtual bool runOnModule(Module &M);
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesAll();
+    }
+  };
 }
 
 char StripSymbols::ID = 0;
@@ -99,6 +112,14 @@ ModulePass *llvm::createStripDebugDeclarePass() {
   return new StripDebugDeclare();
 }
 
+char StripDeadDebugInfo::ID = 0;
+static RegisterPass<StripDeadDebugInfo>
+A("strip-dead-debug-info", "Strip debug info for unused symbols");
+
+ModulePass *llvm::createStripDeadDebugInfoPass() {
+  return new StripDeadDebugInfo();
+}
+
 /// OnlyUsedBy - Return true if V is only used by Usr.
 static bool OnlyUsedBy(Value *V, Value *Usr) {
   for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
@@ -295,3 +316,83 @@ bool StripDebugDeclare::runOnModule(Module &M) {
 
   return true;
 }
+
+/// getRealLinkageName - If special LLVM prefix that is used to inform the asm 
+/// printer to not emit usual symbol prefix before the symbol name is used then
+/// return linkage name after skipping this special LLVM prefix.
+static StringRef getRealLinkageName(StringRef LinkageName) {
+  char One = '\1';
+  if (LinkageName.startswith(StringRef(&One, 1)))
+    return LinkageName.substr(1);
+  return LinkageName;
+}
+
+bool StripDeadDebugInfo::runOnModule(Module &M) {
+  bool Changed = false;
+
+  // Debugging infomration is encoded in llvm IR using metadata. This is designed
+  // such a way that debug info for symbols preserved even if symbols are
+  // optimized away by the optimizer. This special pass removes debug info for 
+  // such symbols.
+
+  // llvm.dbg.gv keeps track of debug info for global variables.
+  if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.gv")) {
+    SmallVector<MDNode *, 8> MDs;
+    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
+      if (DIGlobalVariable(NMD->getOperand(i)).Verify())
+        MDs.push_back(NMD->getOperand(i));
+      else
+        Changed = true;
+    NMD->eraseFromParent();
+    NMD = NULL;
+
+    for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
+           E = MDs.end(); I != E; ++I) {
+      if (M.getGlobalVariable(DIGlobalVariable(*I).getGlobal()->getName(), 
+                              true)) {
+        if (!NMD)
+          NMD = M.getOrInsertNamedMetadata("llvm.dbg.gv");
+        NMD->addOperand(*I);
+      }
+      else
+        Changed = true;
+    }
+  }
+
+  // llvm.dbg.sp keeps track of debug info for subprograms.
+  if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.sp")) {
+    SmallVector<MDNode *, 8> MDs;
+    for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
+      if (DISubprogram(NMD->getOperand(i)).Verify())
+        MDs.push_back(NMD->getOperand(i));
+      else
+        Changed = true;
+    NMD->eraseFromParent();
+    NMD = NULL;
+
+    for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
+           E = MDs.end(); I != E; ++I) {
+      bool FnIsLive = false;
+      if (Function *F = DISubprogram(*I).getFunction())
+        if (M.getFunction(F->getName()))
+          FnIsLive = true;
+      if (FnIsLive) {
+          if (!NMD)
+            NMD = M.getOrInsertNamedMetadata("llvm.dbg.sp");
+          NMD->addOperand(*I);
+      } else {
+        // Remove llvm.dbg.lv.fnname named mdnode which may have been used
+        // to hold debug info for dead function's local variables.
+        StringRef FName = DISubprogram(*I).getLinkageName();
+        if (FName.empty())
+          FName = DISubprogram(*I).getName();
+        if (NamedMDNode *LVNMD = 
+            M.getNamedMetadata(Twine("llvm.dbg.lv.", 
+                                     getRealLinkageName(FName)))) 
+          LVNMD->eraseFromParent();
+      }
+    }
+  }
+
+  return Changed;
+}
diff --git a/llvm/test/Transforms/StripSymbols/2010-07-01-DeadDbgInfo.ll b/llvm/test/Transforms/StripSymbols/2010-07-01-DeadDbgInfo.ll
new file mode 100644
index 00000000000..721f0c8f700
--- /dev/null
+++ b/llvm/test/Transforms/StripSymbols/2010-07-01-DeadDbgInfo.ll
@@ -0,0 +1,47 @@
+; RUN: opt -strip-dead-debug-info | llvm-dis -o %t.ll
+; RUN: grep -v bar %t.ll
+; RUN: grep -v abcd %t.ll
+
+@xyz = global i32 2                               ; <i32*> [#uses=1]
+
+declare void @llvm.dbg.value(metadata, i64, metadata) nounwind readnone
+
+define i32 @fn() nounwind readnone ssp {
+entry:
+  ret i32 0, !dbg !17
+}
+
+define i32 @foo(i32 %i) nounwind readonly ssp {
+entry:
+  tail call void @llvm.dbg.value(metadata !{i32 %i}, i64 0, metadata !14), !dbg !19
+  %.0 = load i32* @xyz, align 4                   ; <i32> [#uses=1]
+  ret i32 %.0, !dbg !20
+}
+
+!llvm.dbg.sp = !{!0, !5, !9}
+!llvm.dbg.lv.bar = !{!12}
+!llvm.dbg.lv.foo = !{!14}
+!llvm.dbg.gv = !{!15, !16}
+
+!0 = metadata !{i32 524334, i32 0, metadata !1, metadata !"bar", metadata !"bar", metadata !"", metadata !1, i32 5, metadata !3, i1 true, i1 true, i32 0, i32 0, null, i1 false, i1 true, null} ; [ DW_TAG_subprogram ]
+!1 = metadata !{i32 524329, metadata !"g.c", metadata !"/tmp/", metadata !2} ; [ DW_TAG_file_type ]
+!2 = metadata !{i32 524305, i32 0, i32 1, metadata !"g.c", metadata !"/tmp/", metadata !"4.2.1 (Based on Apple Inc. build 5658) (LLVM build)", i1 true, i1 true, metadata !"", i32 0} ; [ DW_TAG_compile_unit ]
+!3 = metadata !{i32 524309, metadata !1, metadata !"", metadata !1, i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !4, i32 0, null} ; [ DW_TAG_subroutine_type ]
+!4 = metadata !{null}
+!5 = metadata !{i32 524334, i32 0, metadata !1, metadata !"fn", metadata !"fn", metadata !"fn", metadata !1, i32 6, metadata !6, i1 false, i1 true, i32 0, i32 0, null, i1 false, i1 true, i32 ()* @fn} ; [ DW_TAG_subprogram ]
+!6 = metadata !{i32 524309, metadata !1, metadata !"", metadata !1, i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !7, i32 0, null} ; [ DW_TAG_subroutine_type ]
+!7 = metadata !{metadata !8}
+!8 = metadata !{i32 524324, metadata !1, metadata !"int", metadata !1, i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ]
+!9 = metadata !{i32 524334, i32 0, metadata !1, metadata !"foo", metadata !"foo", metadata !"foo", metadata !1, i32 7, metadata !10, i1 false, i1 true, i32 0, i32 0, null, i1 false, i1 true, i32 (i32)* @foo} ; [ DW_TAG_subprogram ]
+!10 = metadata !{i32 524309, metadata !1, metadata !"", metadata !1, i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !11, i32 0, null} ; [ DW_TAG_subroutine_type ]
+!11 = metadata !{metadata !8, metadata !8}
+!12 = metadata !{i32 524544, metadata !13, metadata !"bb", metadata !1, i32 5, metadata !8} ; [ DW_TAG_auto_variable ]
+!13 = metadata !{i32 524299, metadata !0, i32 5, i32 0} ; [ DW_TAG_lexical_block ]
+!14 = metadata !{i32 524545, metadata !9, metadata !"i", metadata !1, i32 7, metadata !8} ; [ DW_TAG_arg_variable ]
+!15 = metadata !{i32 524340, i32 0, metadata !1, metadata !"abcd", metadata !"abcd", metadata !"", metadata !1, i32 2, metadata !8, i1 true, i1 true, null} ; [ DW_TAG_variable ]
+!16 = metadata !{i32 524340, i32 0, metadata !1, metadata !"xyz", metadata !"xyz", metadata !"", metadata !1, i32 3, metadata !8, i1 false, i1 true, i32* @xyz} ; [ DW_TAG_variable ]
+!17 = metadata !{i32 6, i32 0, metadata !18, null}
+!18 = metadata !{i32 524299, metadata !5, i32 6, i32 0} ; [ DW_TAG_lexical_block ]
+!19 = metadata !{i32 7, i32 0, metadata !9, null}
+!20 = metadata !{i32 10, i32 0, metadata !21, null}
+!21 = metadata !{i32 524299, metadata !9, i32 7, i32 0} ; [ DW_TAG_lexical_block ]