[PATCH] D37364: [DWARF] Line 0 should not have a discriminator

[Robinson, Paul via llvm-commits]

Actually the discriminator is implicitly reset to 0 after every "copy" or special opcode (i.e. after emitting each "row" of the virtual line table) so this change would make the line table *smaller*.  I verified this for the test case.
--paulr

From: llvm-commits [mailto:llvm-commits-bounces at lists.llvm.org] On Behalf Of David Blaikie via llvm-commits
Sent: Thursday, August 31, 2017 7:05 PM
To: reviews+D37364+public+afdebe9cf3065eb2 at reviews.llvm.org; aprantl at apple.com
Cc: jdevlieghere at apple.com; llvm-commits at lists.llvm.org
Subject: Re: [PATCH] D37364: [DWARF] Line 0 should not have a discriminator


Wouldn't this make line tables longer, as it would take extra bits in the line table state machine to change the discriminator back to zero?

On Thu., 31 Aug. 2017, 5:46 pm Paul Robinson via Phabricator <reviews at reviews.llvm.org<mailto:reviews at reviews.llvm.org>> wrote:
probinson created this revision.
Herald added a subscriber: JDevlieghere.

We have line 0 inherit the scope of the previous non-zero line, to limit the size cost of the line 0 records; but that scope might have a discriminator attached, and a discriminator on line 0 is pointless.


https://reviews.llvm.org/D37364

Files:
  lib/CodeGen/AsmPrinter/DwarfDebug.cpp
  test/CodeGen/Generic/dbg-line-0-no-discriminator.ll
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