commit 45a7462094fc204487b71de767fd87eb28a056e6
author Reid Kleckner <rnk@google.com> Fri Jun 30 21:33:44 2017 +0000
committer Reid Kleckner <rnk@google.com> Fri Jun 30 21:33:44 2017 +0000
tree b4e2323e214829ad85d004f88344d4699cfa018e
parent 9eb75c45204781886c8d598a1bc9b5c37f3cb037

[codeview] Use the first valid source location at the top of every MBB

If the instructions at the beginning of the block have no location,
we're better off using the location of the first instruction in the
current basic block. At the very least, that instruction post-dominates
this one, whereas if we don't emit a .cv_loc directive, we end up using
the potentially invalid location that falls through from the previous
block.

We could probably do better here by emitting some kind of ".cv_loc end"
directive that stops the line table entry of the previous .cv_loc
directive from bleeding out of its basic block. This would improve the
line table when an entire MBB has no valid location info.

llvm-svn: 306889

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index e94616f..a81d56e 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -365,7 +365,7 @@
 void CodeViewDebug::maybeRecordLocation(const DebugLoc &DL,
                                         const MachineFunction *MF) {
   // Skip this instruction if it has the same location as the previous one.
-  if (DL == CurFn->LastLoc)
+  if (!DL || DL == PrevInstLoc)
     return;
 
   const DIScope *Scope = DL.get()->getScope();
@@ -385,11 +385,11 @@
   if (!CurFn->HaveLineInfo)
     CurFn->HaveLineInfo = true;
   unsigned FileId = 0;
-  if (CurFn->LastLoc.get() && CurFn->LastLoc->getFile() == DL->getFile())
+  if (PrevInstLoc.get() && PrevInstLoc->getFile() == DL->getFile())
     FileId = CurFn->LastFileId;
   else
     FileId = CurFn->LastFileId = maybeRecordFile(DL->getFile());
-  CurFn->LastLoc = DL;
+  PrevInstLoc = DL;
 
   unsigned FuncId = CurFn->FuncId;
   if (const DILocation *SiteLoc = DL->getInlinedAt()) {
@@ -2150,9 +2150,23 @@
   if (!Asm || !CurFn || MI->isDebugValue() ||
       MI->getFlag(MachineInstr::FrameSetup))
     return;
+
+  // If the first instruction of a new MBB has no location, find the first
+  // instruction with a location and use that.
   DebugLoc DL = MI->getDebugLoc();
-  if (DL == PrevInstLoc || !DL)
+  if (!DL && MI->getParent() != PrevInstBB) {
+    for (const auto &NextMI : *MI->getParent()) {
+      DL = NextMI.getDebugLoc();
+      if (DL)
+        break;
+    }
+  }
+  PrevInstBB = MI->getParent();
+
+  // If we still don't have a debug location, don't record a location.
+  if (!DL)
     return;
+
   maybeRecordLocation(DL, Asm->MF);
 }
 

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
index 2cd495a..fd8f604 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
@@ -118,7 +118,6 @@
 
     SmallVector<LocalVariable, 1> Locals;
 
-    DebugLoc LastLoc;
     const MCSymbol *Begin = nullptr;
     const MCSymbol *End = nullptr;
     unsigned FuncId = 0;