[Bug rtl-optimization/56195] [4.8 Regression] Error: incorrect register `%rdi' used with `l' suffix (at -O2)

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56195

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-02-07 20:02:20 UTC ---
Actually, that one doesn't really work, because we have pseudo rather than hard
reg at that point, which will never simplify.

With this:

--- lra-constraints.c.jj    2013-02-07 18:34:39.000000000 +0100
+++ lra-constraints.c    2013-02-07 20:58:25.558920536 +0100
@@ -421,8 +421,20 @@ get_reload_reg (enum op_type type, enum
       if (rtx_equal_p (curr_insn_input_reloads[i].input, original)
       && in_class_p (curr_insn_input_reloads[i].reg, rclass, &new_class))
     {
-      *result_reg = curr_insn_input_reloads[i].reg;
-      regno = REGNO (*result_reg);
+      rtx reg = curr_insn_input_reloads[i].reg;
+      regno = REGNO (reg);
+      /* If input is equal to original and both are VOIDmode,
+         GET_MODE (reg) might be still different from mode.
+         Ensure we don't return *result_reg with wrong mode.  */
+      if (GET_MODE (reg) != mode)
+        {
+          if (GET_MODE_SIZE (GET_MODE (reg)) < GET_MODE_SIZE (mode))
+        continue;
+          reg = lowpart_subreg (mode, reg, GET_MODE (reg));
+          if (reg == NULL_RTX || GET_CODE (reg) != SUBREG)
+        continue;
+        }
+      *result_reg = reg;
       if (lra_dump_file != NULL)
         {
           fprintf (lra_dump_file, "     Reuse r%d for reload ", regno);

the assembly difference is:

-    cmpl    (%rdi), %rdi
+    cmpl    (%rdi), %edi

which is desirable in this case, but not sure if all get_reload_reg callers
will grok a SUBREG instead of REG returned in *result_reg.