From 25a7174e7a2ef0267486170570380a4dc2d0dd32 Mon Sep 17 00:00:00 2001 From: Adrian Prantl Date: Wed, 1 Oct 2014 17:55:39 +0000 Subject: Move the complex address expression out of DIVariable and into an extra argument of the llvm.dbg.declare/llvm.dbg.value intrinsics. Previously, DIVariable was a variable-length field that has an optional reference to a Metadata array consisting of a variable number of complex address expressions. In the case of OpPiece expressions this is wasting a lot of storage in IR, because when an aggregate type is, e.g., SROA'd into all of its n individual members, the IR will contain n copies of the DIVariable, all alike, only differing in the complex address reference at the end. By making the complex address into an extra argument of the dbg.value/dbg.declare intrinsics, all of the pieces can reference the same variable and the complex address expressions can be uniqued across the CU, too. Down the road, this will allow us to move other flags, such as "indirection" out of the DIVariable, too. The new intrinsics look like this: declare void @llvm.dbg.declare(metadata %storage, metadata %var, metadata %expr) declare void @llvm.dbg.value(metadata %storage, i64 %offset, metadata %var, metadata %expr) This patch adds a new LLVM-local tag to DIExpressions, so we can detect and pretty-print DIExpression metadata nodes. What this patch doesn't do: This patch does not touch the "Indirect" field in DIVariable; but moving that into the expression would be a natural next step. http://reviews.llvm.org/D4919 rdar://problem/17994491 Thanks to dblaikie and dexonsmith for reviewing this patch! llvm-svn: 218778 --- llvm/docs/SourceLevelDebugging.rst | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) (limited to 'llvm/docs/SourceLevelDebugging.rst') diff --git a/llvm/docs/SourceLevelDebugging.rst b/llvm/docs/SourceLevelDebugging.rst index f7b62cb0872..8acd90122b4 100644 --- a/llvm/docs/SourceLevelDebugging.rst +++ b/llvm/docs/SourceLevelDebugging.rst @@ -571,7 +571,7 @@ Local variables metadata, ;; Reference to the type descriptor i32, ;; flags metadata ;; (optional) Reference to inline location - metadata ;; (optional) Reference to a complex expression (see below) + metadata ;; (optional) Reference to a complex expression. } These descriptors are used to define variables local to a sub program. The @@ -590,7 +590,20 @@ The context is either the subprogram or block where the variable is defined. Name the source variable name. Context and line indicate where the variable was defined. Type descriptor defines the declared type of the variable. -The ``OpPiece`` operator is used for (typically larger aggregate) +Complex Expressions +^^^^^^^^^^^^^^^^^^^ +.. code-block:: llvm + + !8 = metadata !{ + i32, ;; DW_TAG_expression + ... + } + +Complex expressions describe variable storage locations in terms of +prefix-notated DWARF expressions. Currently the only supported +operators are ``DW_OP_plus``, ``DW_OP_deref``, and ``DW_OP_piece``. + +The ``DW_OP_piece`` operator is used for (typically larger aggregate) variables that are fragmented across several locations. It takes two i32 arguments, an offset and a size in bytes to describe which piece of the variable is at this location. -- cgit v1.2.3