[DWARF] Handle the DW_OP_entry_value operand

Add the IR and the AsmPrinter parts for handling of the DW_OP_entry_values
DWARF operation.

([11/13] Introduce the debug entry values.)

Co-authored-by: Ananth Sowda <asowda@cisco.com>
Co-authored-by: Nikola Prica <nikola.prica@rt-rk.com>
Co-authored-by: Ivan Baev <ibaev@cisco.com>

Differential Revision: https://reviews.llvm.org/D60866

llvm-svn: 364542

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 7b74971c817..2322bbfd7a6 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -4729,6 +4729,17 @@ The current supported opcode vocabulary is limited:
   of the stack is treated as an address. The second stack entry is treated as an
   address space identifier.
 - ``DW_OP_stack_value`` marks a constant value.
+- If an expression is marked with ``DW_OP_entry_value`` all register and
+  memory read operations refer to the respective value at the function entry.
+  The first operand of ``DW_OP_entry_value`` is the size of following
+  DWARF expression.
+  ``DW_OP_entry_value`` may appear after the ``LiveDebugValues`` pass.
+  LLVM only supports entry values for function parameters
+  that are unmodified throughout a function and that are described as
+  simple register location descriptions.
+  ``DW_OP_entry_value`` may also appear after the ``AsmPrinter`` pass when
+  a call site parameter value (``DW_AT_call_site_parameter_value``)
+  is represented as entry value of the parameter.
 
 DWARF specifies three kinds of simple location descriptions: Register, memory,
 and implicit location descriptions.  Note that a location description is