[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, 8 insertions, 1 deletions

diff --git a/llvm/test/DebugInfo/X86/debug-loc-frame.ll b/llvm/test/DebugInfo/X86/debug-loc-frame.ll
index 58b11857a45..f3bcfcb7377 100644
--- a/llvm/test/DebugInfo/X86/debug-loc-frame.ll
+++ b/llvm/test/DebugInfo/X86/debug-loc-frame.ll
@@ -28,7 +28,14 @@
 ; CHECK:      DW_TAG_variable
 ; CHECK:      DW_AT_location [DW_FORM_sec_offset] ({{.*}}
 ; CHECK-NEXT:   [{{0x.*}}, {{0x.*}}): DW_OP_reg0 RAX
-; CHECK-NEXT:   [{{0x.*}}, {{0x.*}}): DW_OP_breg7 RSP+4, DW_OP_deref)
+;
+; Note: This is a location, so we don't want an extra DW_OP_deref at the end.
+; LLDB gets the location right without it:
+;     Variable:  ... name = "val", type = "int", location =  [rsp+4], decl = frame.c:10
+; Adding the deref actually creates an invalid location:
+;     ... [rsp+4] DW_OP_deref
+;
+; CHECK-NEXT:   [{{0x.*}}, {{0x.*}}): DW_OP_breg7 RSP+4)
 ; CHECK-NEXT: DW_AT_name {{.*}}"val"
 
 ; ModuleID = 'frame.c'