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| author | Florian Hahn <florian.hahn@arm.com> | 2017-06-14 13:14:38 +0000 |
|---|---|---|
| committer | Florian Hahn <florian.hahn@arm.com> | 2017-06-14 13:14:38 +0000 |
| commit | 50963b3b75627a63ddceb22ef2b80b5c16c0a028 (patch) | |
| tree | e95cc2f1628aa29735f47754252c2df7f19b5589 /docs | |
| parent | 3e4134fdf135182419fa5ddc8a2a5ab4abdab480 (diff) | |
Align definition of DW_OP_plus with DWARF spec [3/3]
Summary:
This patch is part of 3 patches that together form a single patch, but must be introduced in stages in order not to break things.
The way that LLVM interprets DW_OP_plus in DIExpression nodes is basically that of the DW_OP_plus_uconst operator since LLVM expects an unsigned constant operand. This unnecessarily restricts the DW_OP_plus operator, preventing it from being used to describe the evaluation of runtime values on the expression stack. These patches try to align the semantics of DW_OP_plus and DW_OP_minus with that of the DWARF definition, which pops two elements off the expression stack, performs the operation and pushes the result back on the stack.
This is done in three stages:
• The first patch (LLVM) adds support for DW_OP_plus_uconst.
• The second patch (Clang) contains changes all its uses from DW_OP_plus to DW_OP_plus_uconst.
• The third patch (LLVM) changes the semantics of DW_OP_plus and DW_OP_minus to be in line with its DWARF meaning. This patch includes the bitcode upgrade from legacy DIExpressions.
Patch by Sander de Smalen.
Reviewers: echristo, pcc, aprantl
Reviewed By: aprantl
Subscribers: fhahn, javed.absar, aprantl, llvm-commits
Differential Revision: https://reviews.llvm.org/D33894
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305386 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/LangRef.rst | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/docs/LangRef.rst b/docs/LangRef.rst index 24362825d822..ec445489d8b9 100644 --- a/docs/LangRef.rst +++ b/docs/LangRef.rst @@ -4404,7 +4404,11 @@ referenced LLVM variable relates to the source language variable. The current supported vocabulary is limited: - ``DW_OP_deref`` dereferences the top of the expression stack. -- ``DW_OP_plus, 93`` adds ``93`` to the working expression. +- ``DW_OP_plus`` pops the last two entries from the expression stack, adds + them together and appends the result to the expression stack. +- ``DW_OP_minus`` pops the last two entries from the expression stack, subtracts + the last entry from the second last entry and appends the result to the + expression stack. - ``DW_OP_plus_uconst, 93`` adds ``93`` to the working expression. - ``DW_OP_LLVM_fragment, 16, 8`` specifies the offset and size (``16`` and ``8`` here, respectively) of the variable fragment from the working expression. Note @@ -4427,10 +4431,10 @@ combined with a concrete location. .. code-block:: llvm !0 = !DIExpression(DW_OP_deref) - !1 = !DIExpression(DW_OP_plus, 3) !1 = !DIExpression(DW_OP_plus_uconst, 3) + !1 = !DIExpression(DW_OP_constu, 3, DW_OP_plus) !2 = !DIExpression(DW_OP_bit_piece, 3, 7) - !3 = !DIExpression(DW_OP_deref, DW_OP_plus, 3, DW_OP_LLVM_fragment, 3, 7) + !3 = !DIExpression(DW_OP_deref, DW_OP_constu, 3, DW_OP_plus, DW_OP_LLVM_fragment, 3, 7) !4 = !DIExpression(DW_OP_constu, 2, DW_OP_swap, DW_OP_xderef) !5 = !DIExpression(DW_OP_constu, 42, DW_OP_stack_value) |