Clean up the processing of dbg.value in various places

Summary:
First up is instcombine, where in the dbg.declare -> dbg.value conversion,
the llvm.dbg.value needs to be called on the actual loaded value, rather
than the address (since the whole point of this transformation is to be
able to get rid of the alloca). Further, now that that's cleaned up, we
can remove a hack in the backend, that would add an implicit OP_deref if
the argument to dbg.value was an alloca. This stems from before the
existence of DIExpression and is no longer necessary since the deref can
be expressed explicitly.

Now, in order to make sure that the tests pass with this change, we need to
correct the printing of DEBUG_VALUE comments to take into account the
expression, which wasn't taken into account before.

Unfortunately, for both these changes, there were a number of incorrect
test cases (mostly the wrong number of DW_OP_derefs, but also a couple
where the test itself was broken more badly). aprantl and I have gone
through and adjusted these test case in order to make them pass with
these fixes and in some cases to make sure they're actually testing
what they are meant to test.

Reviewers: aprantl

Subscribers: dsanders

Differential Revision: http://reviews.llvm.org/D14186

llvm-svn: 256077

1 files changed, 13 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 31039816e14..e75163f323d 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1071,8 +1071,13 @@ bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
   if (LdStHasDebugValue(DIVar, LI))
     return true;
 
-  Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, DIVar, DIExpr,
-                                  DDI->getDebugLoc(), LI);
+  // We are now tracking the loaded value instead of the address. In the
+  // future if multi-location support is added to the IR, it might be
+  // preferable to keep tracking both the loaded value and the original
+  // address in case the alloca can not be elided.
+  Instruction *DbgValue = Builder.insertDbgValueIntrinsic(
+      LI, 0, DIVar, DIExpr, DDI->getDebugLoc(), (Instruction *)nullptr);
+  DbgValue->insertAfter(LI);
   return true;
 }
 
@@ -1114,9 +1119,13 @@ bool llvm::LowerDbgDeclare(Function &F) {
           // This is a call by-value or some other instruction that
           // takes a pointer to the variable. Insert a *value*
           // intrinsic that describes the alloca.
+          SmallVector<uint64_t, 1> NewDIExpr;
+          auto *DIExpr = DDI->getExpression();
+          NewDIExpr.push_back(dwarf::DW_OP_deref);
+          NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
           DIB.insertDbgValueIntrinsic(AI, 0, DDI->getVariable(),
-                                      DDI->getExpression(), DDI->getDebugLoc(),
-                                      CI);
+                                      DIB.createExpression(NewDIExpr),
+                                      DDI->getDebugLoc(), CI);
         }
       DDI->eraseFromParent();
     }