Re: [PATCH] Fix subreg in debug_insn handling issue exposed on mn103

[Jeff Law]

On 04/13/2017 08:06 AM, Jakub Jelinek wrote:

On Thu, Apr 13, 2017 at 08:03:48AM -0600, Jeff Law wrote:

The mn103 port fails to build newlib/libgcc because it's got a
non-simplifyable (subreg (mem)) in a debug insn.

reload will call eliminate_regs_1 on the debug insn.  It'll see the subreg
and call gen_rtx_SUBREG.  That asserts that the subreg is valid. Which (of
course) fails.

The key here is that validity of a subreg expression varies depending on
whether or not it appears in a DEBUG_INSN or elsewhere.


The fix is to have reload use gen_rtx_raw_SUBREG for subregs appearing in
DEBUG_INSNs.  Doing so allows the mn103 port to build libgcc and newlib
successfully.  LRA may also be affected (by inspection), but I haven't tried
to fix it without a way to trigger the issue.

This has been further tested by building most of the *-elf, *-gnu and
*-rtems targets through to newlib, glibc and newlib respectively.  The
exceptions that fail do so for completely unrelated reasons.

While it shouldn't trigger anything, I also did a bootstrap & regression
test cycle on x86_64-linux-gnu for sanity's sake.

This is a regression -- mn103 has certainly built libgcc/newlib in the past.
Installing on the trunk,

ENOPATCH.  But what you describe looks reasonable.

Bah.  Attached.


Jeff

commit e716863933c0cb1db0ba63d014ea989d8ff45c40
Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Thu Apr 13 14:02:33 2017 +0000

        * reload1.c (eliminate_regs_1): Call gen_rtx_raw_SUBREG for SUBREGs
        appearing in DEBUG_INSNs.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@246904 
138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 740ca66..caec440 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2017-04-13  Jeff Law  <l...@redhat.com>
+
+       * reload1.c (eliminate_regs_1): Call gen_rtx_raw_SUBREG for SUBREGs
+       appearing in DEBUG_INSNs.
+
 2017-04-13  Martin Liska  <mli...@suse.cz>
 
        PR gcov-profile/80413
diff --git a/gcc/reload1.c b/gcc/reload1.c
index c1ce7ca..4dc118e 100644
--- a/gcc/reload1.c
+++ b/gcc/reload1.c
@@ -2831,6 +2831,8 @@ eliminate_regs_1 (rtx x, machine_mode mem_mode, rtx insn,
                  || x_size == new_size)
              )
            return adjust_address_nv (new_rtx, GET_MODE (x), SUBREG_BYTE (x));
+         else if (insn && GET_CODE (insn) == DEBUG_INSN)
+           return gen_rtx_raw_SUBREG (GET_MODE (x), new_rtx, SUBREG_BYTE (x));
          else
            return gen_rtx_SUBREG (GET_MODE (x), new_rtx, SUBREG_BYTE (x));
        }