RE: [PATCH] Alternate fix to PR target/96558: Robustify ix86_expand_clear.

[Roger Sayle]

Doh! ENOPATCH.

-----Original Message-----
From: Roger Sayle <ro...@nextmovesoftware.com> 
Sent: 13 August 2020 09:29
To: 'GCC Patches' <gcc-patches@gcc.gnu.org>
Cc: 'Uros Bizjak' <ubiz...@gmail.com>
Subject: [PATCH] Alternate fix to PR target/96558: Robustify
ix86_expand_clear.


This patch is an alternate/supplementary fix to the recent regression PR
target/96558.  Currently ix86_expand_clear may/should only be called with a
general register DEST after reload_completed.  With the simple change below,
this function now checks these conditions itself, and does the right thing
(or at least something reasonable) rather than ICE.

This change alone is sufficient to fix the recent regression, and allow the
recently added testcase to pass, but following the "why fix something just
once" maxim, I propose adding both solutions (to reduce the risk of
surprises in the future).  Leaving the peephole2 fix in place is reasonable,
as scheduling or a later pass eventually move the condition code setter/use
next to each other, so moving the vpxor with the
peephole2 provides no (additional) benefit.  i.e. gcc.dg/pr96558.c contains:

        vpxor   %xmm0, %xmm0, %xmm0
        testl   %eax, %eax
        jne     .L91

This patch has been tested on x86_64-pc-linux-gnu (without the peephole2
solution) with a make bootstrap and make -k check with no new failures, but
allows the recently added testcase to pass.

Ok for mainline?


2020-08-19  Roger Sayle  <ro...@nextmovesoftware.com>

gcc/ChangeLog
        PR target/96558
        * config/i386/i386-expand.c (ix86_expand_clear): Explicitly
        test for reload_completed and GENERAL_REG_P, and emit a simple
        set of const0_rtx otherwise.

Thanks in advance.
Sorry for the inconvenience.
Roger
--
Roger Sayle
NextMove Software
Cambridge, UK


diff --git a/gcc/config/i386/i386-expand.c b/gcc/config/i386/i386-expand.c
index f441ba9..cf3e741 100644
--- a/gcc/config/i386/i386-expand.c
+++ b/gcc/config/i386/i386-expand.c
@@ -164,18 +164,22 @@ ix86_expand_clear (rtx dest)
   rtx tmp;
 
   /* We play register width games, which are only valid after reload.  */
-  gcc_assert (reload_completed);
-
-  /* Avoid HImode and its attendant prefix byte.  */
-  if (GET_MODE_SIZE (GET_MODE (dest)) < 4)
-    dest = gen_rtx_REG (SImode, REGNO (dest));
-  tmp = gen_rtx_SET (dest, const0_rtx);
-
-  if (!TARGET_USE_MOV0 || optimize_insn_for_size_p ())
+  if (reload_completed && GENERAL_REG_P (dest))
     {
-      rtx clob = gen_rtx_CLOBBER (VOIDmode, gen_rtx_REG (CCmode, FLAGS_REG));
-      tmp = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, tmp, clob));
+      /* Avoid HImode and its attendant prefix byte.  */
+      if (GET_MODE_SIZE (GET_MODE (dest)) < 4)
+        dest = gen_rtx_REG (SImode, REGNO (dest));
+      tmp = gen_rtx_SET (dest, const0_rtx);
+
+      if (!TARGET_USE_MOV0 || optimize_insn_for_size_p ())
+       {
+         rtx clob = gen_rtx_CLOBBER (VOIDmode,
+                                     gen_rtx_REG (CCmode, FLAGS_REG));
+         tmp = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, tmp, clob));
+       }
     }
+  else
+    tmp = gen_rtx_SET (dest, const0_rtx);
 
   emit_insn (tmp);
 }