Before this patch every Swift function would contain a top-level
DW_TAG_lexical_scope that didn't provide any useful information, used extra
space in the debug info and prevented local variables from showing up in virtual
async backtraces.
Summary:
CodeView does not recognize zero as an artificial line location
and so a line location of zero causes unexpected behavior when
stepping through user code. If we find a line location of zero
and our scope has not changed, we use the most recent debug
location. That is expected to be the user code that most likely
relates to the current instruction and is similar to the behavior
in LLDB.
Test Plan:
test/DebugInfo/linetable-codeview.swift
LLVM r336847 changed FileCheck's CHECK-DAG feature to stop supporting
overlapping matches. I already fixed one test by invoking FileCheck with the
-allow-deprecated-dag-overlap option, but it turns out there are a bunch
more of them. This change applies the same workaround to all of them.
LLVM r336847 changed FileCheck's CHECK-DAG feature to stop supporting
overlapping matches. That breaks the DebugInfo/columns.swift test.
This change works around the failure by invoking FileCheck with the
--allow-deprecated-dag-overlap option. I filed a bug report to track
fixing the test properly (https://bugs.swift.org/browse/SR-8359).
Summary:
There are a few problems with how Swift currently emits location
information for CodeView.
1. WinDbg does not work well with column information so all column
locations must be set to zero.
2. Some instructions, e.g., ``a + b``, will emit ``@llvm.trap()``
and ``unreachable``. Those instructions should have artificial
locations, i.e., they should have a line location of zero.
3. Some instructions, e.g., ``a / b``, will emit ``unreachable``
sandwiched between other code for that instruction. This makes
WinDbg confused and it cannot decide which set of instructions
to break on. Those instructions should have the same line location
as the others.
4. There are several prologue instructions with artificial line
locations that create breaks in the linetables. Those instructions
should have valid line locations, usually at the start of the
function.
5. Case bodies have cleanup instructions with artificial line
locations unless it has a ``do`` block. Those locations should
be the last line in the case block.
Test Plan:
test/DebugInfo/basic.swift
test/DebugInfo/columns.swift
test/DebugInfo/linetable-codeview.swift
test/DebugInfo/line-directive-codeview.swift
