commit c4e08feb002ffc32d0f37505134c4eddb1a784f7
author David Blaikie <dblaikie@gmail.com> Tue Dec 18 01:06:09 2018 +0000
committer David Blaikie <dblaikie@gmail.com> Tue Dec 18 01:06:09 2018 +0000
tree 2a0b2851aa8132c1de878d99db28ab91dad0144a
parent 48a28c166518e238bb7c7b305f1473e75bc5ea7d

Recommit r348806: DebugInfo: Use symbol difference for CU length to simplify assembly reading/editing

Mucking about simplifying a test case ( https://reviews.llvm.org/D55261 ) I stumbled across something I've hit before - that LLVM's (GCC's does too, FWIW) assembly output includes a hardcode length for a DWARF unit in its header. Instead we could emit a label difference - making the assembly easier to read/edit (though potentially at a slight (I haven't tried to observe it) performance cost of delaying/sinking the length computation into the MC layer).

Fix: Predicated all the changes (including creating the labels, even if they aren't used/needed) behind the NVPTX useSectionsAsReferences, avoiding emitting labels in NVPTX where ptxas can't parse them.

Reviewers: JDevlieghere, probinson, ABataev

Differential Revision: https://reviews.llvm.org/D55281

llvm-svn: 349430

llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp
index 0bfa1d4..78ccad4 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp
@@ -47,6 +47,9 @@
   Asm->OutStreamer->SwitchSection(S);
   TheU->emitHeader(UseOffsets);
   Asm->emitDwarfDIE(TheU->getUnitDie());
+
+  if (MCSymbol *EndLabel = TheU->getEndLabel())
+    Asm->OutStreamer->EmitLabel(EndLabel);
 }
 
 // Compute the size and offset for each DIE.

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index 062eb3a..991dac7 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -1553,7 +1553,14 @@
 void DwarfUnit::emitCommonHeader(bool UseOffsets, dwarf::UnitType UT) {
   // Emit size of content not including length itself
   Asm->OutStreamer->AddComment("Length of Unit");
-  Asm->emitInt32(getHeaderSize() + getUnitDie().getSize());
+  if (!DD->useSectionsAsReferences()) {
+    StringRef Prefix = isDwoUnit() ? "debug_info_dwo_" : "debug_info_";
+    MCSymbol *BeginLabel = Asm->createTempSymbol(Prefix + "start");
+    EndLabel = Asm->createTempSymbol(Prefix + "end");
+    Asm->EmitLabelDifference(EndLabel, BeginLabel, 4);
+    Asm->OutStreamer->EmitLabel(BeginLabel);
+  } else
+    Asm->emitInt32(getHeaderSize() + getUnitDie().getSize());
 
   Asm->OutStreamer->AddComment("DWARF version number");
   unsigned Version = DD->getDwarfVersion();

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
index c5cb7e1..a59ebb7 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h
@@ -49,6 +49,9 @@
   /// Target of Dwarf emission.
   AsmPrinter *Asm;
 
+  /// Emitted at the end of the CU and used to compute the CU Length field.
+  MCSymbol *EndLabel = nullptr;
+
   // Holders for some common dwarf information.
   DwarfDebug *DD;
   DwarfFile *DU;
@@ -82,6 +85,7 @@
 public:
   // Accessors.
   AsmPrinter* getAsmPrinter() const { return Asm; }
+  MCSymbol *getEndLabel() const { return EndLabel; }
   uint16_t getLanguage() const { return CUNode->getSourceLanguage(); }
   const DICompileUnit *getCUNode() const { return CUNode; }