[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338069 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 2 deletions

diff --git a/unittests/IR/MetadataTest.cpp b/unittests/IR/MetadataTest.cpp
index 12256bd2366..84a7b02fa98 100644
--- a/unittests/IR/MetadataTest.cpp
+++ b/unittests/IR/MetadataTest.cpp
@@ -2111,14 +2111,20 @@ TEST_F(DIExpressionTest, get) {
   // Test DIExpression::prepend().
   uint64_t Elts0[] = {dwarf::DW_OP_LLVM_fragment, 0, 32};
   auto *N0 = DIExpression::get(Context, Elts0);
-  N0 = DIExpression::prepend(N0, true, 64, true, true);
+  auto *N0WithPrependedOps = DIExpression::prepend(N0, true, 64, true, true);
   uint64_t Elts1[] = {dwarf::DW_OP_deref,
                       dwarf::DW_OP_plus_uconst, 64,
                       dwarf::DW_OP_deref,
                       dwarf::DW_OP_stack_value,
                       dwarf::DW_OP_LLVM_fragment, 0, 32};
   auto *N1 = DIExpression::get(Context, Elts1);
-  EXPECT_EQ(N0, N1);
+  EXPECT_EQ(N0WithPrependedOps, N1);
+
+  // Test DIExpression::append().
+  uint64_t Elts2[] = {dwarf::DW_OP_deref, dwarf::DW_OP_plus_uconst, 64,
+                      dwarf::DW_OP_deref, dwarf::DW_OP_stack_value};
+  auto *N2 = DIExpression::append(N0, Elts2);
+  EXPECT_EQ(N0WithPrependedOps, N2);
 }
 
 TEST_F(DIExpressionTest, isValid) {