[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, 4 insertions, 1 deletions

diff --git a/llvm/test/DebugInfo/AArch64/coalescing.ll b/llvm/test/DebugInfo/AArch64/coalescing.ll
index 0f65856fcb3..c39f8841948 100644
--- a/llvm/test/DebugInfo/AArch64/coalescing.ll
+++ b/llvm/test/DebugInfo/AArch64/coalescing.ll
@@ -20,10 +20,13 @@ entry:
   %0 = bitcast i32* %size to i8*, !dbg !15
   %call = call i8* @_Z3fooPv(i8* %0) #3, !dbg !15
   call void @llvm.dbg.value(metadata i32* %size, metadata !10, metadata !16), !dbg !17
+
+  ; The *location* of the variable should be $sp+12. This tells the debugger to
+  ; look up its value in [$sp+12].
   ; CHECK: .debug_info contents:
   ; CHECK: DW_TAG_variable
   ; CHECK-NEXT: DW_AT_location
-  ; CHECK-NEXT: DW_OP_breg31 WSP+12, DW_OP_deref
+  ; CHECK-NEXT: DW_OP_breg31 WSP+12
   ; CHECK-NEXT: DW_AT_name {{.*}}"size"
   ret void, !dbg !18
 }