Re: [PATCH, GCC] PR target/86487: fix the way 'uses_hard_regs_p' handles paradoxical subregs

[Vladimir Makarov <vmakarov@redhat.com>]

On 2019-02-13 5:54 a.m., Andre Vieira (lists) wrote:
> PING.
>
> Since Jeff is away can another maintainer have a look at this please?
>
>
I see the following patch

diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index c061093ed699620afe2dfda60d58066d6967523a..736b084acc552b75ff4d369b6584bc9ab422e21b 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -1761,11 +1761,21 @@ uses_hard_regs_p (rtx x, HARD_REG_SET set)
      return false;
    code = GET_CODE (x);
    mode = GET_MODE (x);
+
    if (code == SUBREG)
      {
+      /* For all SUBREGs we want to check whether the full multi-register
+	 overlaps the set.  For normal SUBREGs this means 'get_hard_regno' of
+	 the inner register, for paradoxical SUBREGs this means the
+	 'get_hard_regno' of the full SUBREG and for complete SUBREGs either is
+	 fine.  Use the wider mode for all cases.  */
+      rtx subreg = SUBREG_REG (x);
        mode = wider_subreg_mode (x);
-      x = SUBREG_REG (x);
-      code = GET_CODE (x);
+      if (mode == GET_MODE (subreg))
+	{
+	  x = subreg;
+	  code = GET_CODE (x);
+	}
      }
  
    if (REG_P (x))

In your case, x will be SUBREG and be processed recursively only as a register of subreg.

I think you need to change the last line on

   if (REG_P (x) || code == SUBREG)

then the subreg will processed by get_hard_regno as subreg.