DWARF: Track sequences so that we can handle reordering within one (#2932)

Previously we tracked sequence ends, so if an instruction was marked
as the end, we'd keep marking it that way in the output. However, if
X, Y, Z form a sequence that is then reordered into Z, Y, X then we need
to emit the end on X now.

To do that, give a "sequence number" to each debug line. Then when
emitting, we can tell if two adjacent lines are in a sequence or not, and
emit the end properly.

This fixes a large partner testcase, allowing
llvm-dwarfdump --verify --debug-line to pass on it.

With this change it is easier to remove the hackish handling of
prologueEnd that we had before, where we reset it. Instead, just
emit it when it is set, and that's all. In particular we can get rid
of the // Reset the state and resetAfterLine() calls in emitDiff.
That function now just emits a diff, with no side effects, and is
marked const.

This refactoring moves the needToEmit() check to an earlier
place. Instead of noting lines we'll never emit, don't even note them
at all.

The test diff seems large, but it is all due to one small change that
then changes all the later offsets:

- 0x00000831: 01 DW_LNS_copy
-             0x000000000000086e     43      4      1   0             0  is_stmt
+ 0x00000831: 00 DW_LNE_end_sequence
+             0x000000000000086e     43      4      1   0             0  is_stmt end_sequence

Note how we add end_sequence there. We used to have an entry
right after it with line 0 that was marked as the end of the sequence.
In the new code, we don't emit that unnecessary line (which was
previously only emitted for the end sequence!) and instead emit
the end sequence on the last valid line.

0 files changed, 0 insertions, 0 deletions