[SelectionDAG] Improve handling of dangling debug info

Summary:
1) Make sure to discard dangling debug info if the variable (or
variable fragment) is mapped to something new before we had a
chance to resolve the dangling debug info.

2) When resolving debug info, make sure to bump the associated
SDNodeOrder to ensure that the DBG_VALUE is emitted after the
instruction that defines the value used in the DBG_VALUE.
This will avoid a debug-use before def scenario as seen in
https://bugs.llvm.org/show_bug.cgi?id=36417.

The new test case, test/DebugInfo/X86/sdag-dangling-dbgvalue.ll,
show some other limitations in how dangling debug info is
handled in the SelectionDAG. Since we currently only support
having one dangling dbg.value per Value, we will end up dropping
debug info when there are more than one variable that is described
by the same "dangling value".

Reviewers: aprantl

Reviewed By: aprantl

Subscribers: aprantl, eraman, llvm-commits, JDevlieghere

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D44369

llvm-svn: 327303

1 files changed, 2 insertions, 25 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
index 2e5c2244793..edf66e93058 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
@@ -123,29 +123,6 @@ MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
   return LabelsAfterInsn.lookup(MI);
 }
 
-int DebugHandlerBase::fragmentCmp(const DIExpression *P1,
-                                  const DIExpression *P2) {
-  auto Fragment1 = *P1->getFragmentInfo();
-  auto Fragment2 = *P2->getFragmentInfo();
-  unsigned l1 = Fragment1.OffsetInBits;
-  unsigned l2 = Fragment2.OffsetInBits;
-  unsigned r1 = l1 + Fragment1.SizeInBits;
-  unsigned r2 = l2 + Fragment2.SizeInBits;
-  if (r1 <= l2)
-    return -1;
-  else if (r2 <= l1)
-    return 1;
-  else
-    return 0;
-}
-
-bool DebugHandlerBase::fragmentsOverlap(const DIExpression *P1,
-                                        const DIExpression *P2) {
-  if (!P1->isFragment() || !P2->isFragment())
-    return true;
-  return fragmentCmp(P1, P2) == 0;
-}
-
 /// If this type is derived from a base type then return base type size.
 uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
   DIType *Ty = TyRef.resolve();
@@ -232,8 +209,8 @@ void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
           const DIExpression *Fragment = I->first->getDebugExpression();
           if (std::all_of(Ranges.begin(), I,
                           [&](DbgValueHistoryMap::InstrRange Pred) {
-                            return !fragmentsOverlap(
-                                Fragment, Pred.first->getDebugExpression());
+                            return !Fragment->fragmentsOverlap(
+                                Pred.first->getDebugExpression());
                           }))
             LabelsBeforeInsn[I->first] = Asm->getFunctionBegin();
           else