[DebugInfo] Introduce DW_OP_LLVM_convert

Introduce a DW_OP_LLVM_convert Dwarf expression pseudo op that allows
for a convenient way to perform type conversions on the Dwarf expression
stack. As an additional bonus it paves the way for using other Dwarf
v5 ops that need to reference a base_type.

The new DW_OP_LLVM_convert is used from lib/Transforms/Utils/Local.cpp
to perform sext/zext on debug values but mainly the patch is about
preparing terrain for adding other Dwarf v5 ops that need to reference a
base_type.

For Dwarf v5 the op maps to DW_OP_convert and for earlier versions a
complex shift & mask pattern is generated to emulate sext/zext.

This is a recommit of r356442 with trivial fixes for the failing tests.

Differential Revision: https://reviews.llvm.org/D56587

llvm-svn: 356451

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index fcea8a482a7..a43b0ee3c45 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -4682,6 +4682,10 @@ The current supported opcode vocabulary is limited:
   here, respectively) of the variable fragment from the working expression. Note
   that contrary to DW_OP_bit_piece, the offset is describing the location
   within the described source variable.
+- ``DW_OP_LLVM_convert, 16, DW_ATE_signed`` specifies a bit size and encoding
+  (``16`` and ``DW_ATE_signed`` here, respectively) to which the top of the
+  expression stack is to be converted. Maps into a ``DW_OP_convert`` operation
+  that references a base type constructed from the supplied values.
 - ``DW_OP_swap`` swaps top two stack entries.
 - ``DW_OP_xderef`` provides extended dereference mechanism. The entry at the top
   of the stack is treated as an address. The second stack entry is treated as an