[DebugInfo] LowerDbgDeclare: Add derefs when handling CallInst users

LowerDbgDeclare inserts a dbg.value before each use of an address
described by a dbg.declare. When inserting a dbg.value before a CallInst
use, however, it fails to append DW_OP_deref to the DIExpression.

The DW_OP_deref is needed to reflect the fact that a dbg.value describes
a source variable directly (as opposed to a dbg.declare, which relies on
pointer indirection).

This patch adds in the DW_OP_deref where needed. This results in the
correct values being shown during a debug session for a program compiled
with ASan and optimizations (see https://reviews.llvm.org/D49520). Note
that ConvertDebugDeclareToDebugValue is already correct -- no changes
there were needed.

One complication is that SelectionDAG is unable to distinguish between
direct and indirect frame-index (FRAMEIX) SDDbgValues. This patch also
fixes this long-standing issue in order to not regress integration tests
relying on the incorrect assumption that all frame-index SDDbgValues are
indirect. This is a necessary fix: the newly-added DW_OP_derefs cannot
be lowered properly otherwise. Basically the fix prevents a direct
SDDbgValue with DIExpression(DW_OP_deref) from being dereferenced twice
by a debugger. There were a handful of tests relying on this incorrect
"FRAMEIX => indirect" assumption which actually had incorrect
DW_AT_locations: these are all fixed up in this patch.

Testing:

- check-llvm, and an end-to-end test using lldb to debug an optimized
  program.
- Existing unit tests for DIExpression::appendToStack fully cover the
  new DIExpression::append utility.
- check-debuginfo (the debug info integration tests)

Differential Revision: https://reviews.llvm.org/D49454

llvm-svn: 338069

1 files changed, 9 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp b/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
index 65ee3816f84..d6171f3177d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
@@ -697,11 +697,15 @@ InstrEmitter::EmitDbgValue(SDDbgValue *SD,
   if (SD->getKind() == SDDbgValue::FRAMEIX) {
     // Stack address; this needs to be lowered in target-dependent fashion.
     // EmitTargetCodeForFrameDebugValue is responsible for allocation.
-    return BuildMI(*MF, DL, TII->get(TargetOpcode::DBG_VALUE))
-        .addFrameIndex(SD->getFrameIx())
-        .addImm(0)
-        .addMetadata(Var)
-        .addMetadata(Expr);
+    auto FrameMI = BuildMI(*MF, DL, TII->get(TargetOpcode::DBG_VALUE))
+                       .addFrameIndex(SD->getFrameIx());
+    if (SD->isIndirect())
+      // Push [fi + 0] onto the DIExpression stack.
+      FrameMI.addImm(0);
+    else
+      // Push fi onto the DIExpression stack.
+      FrameMI.addReg(0);
+    return FrameMI.addMetadata(Var).addMetadata(Expr);
   }
   // Otherwise, we're going to create an instruction here.
   const MCInstrDesc &II = TII->get(TargetOpcode::DBG_VALUE);