[PATCH 3/3] VAX: Handle subtracting from self with QMATH DImode add/sub

[Maciej W. Rozycki]

Remove an assertion the failure of which has not been actually observed, 
but which appears clearly dangerous, for when the QMATH DImode add/sub 
handler is invoked with the subtrahend and the minuend both the same.
Instead handle the operation by emitting a move of constant 0 to the 
output operand.  Adjust the relevant inline comment accordingly.

        gcc/
        * config/vax/vax.c (vax_expand_addsub_di_operands): Handle equal
        input operands with subtraction.
---
 gcc/config/vax/vax.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Index: gcc/gcc/config/vax/vax.c
===================================================================
--- gcc.orig/gcc/config/vax/vax.c
+++ gcc/gcc/config/vax/vax.c
@@ -2042,12 +2042,14 @@ vax_expand_addsub_di_operands (rtx * ope
     }
   else
     {
-      /* If are adding the same value together, that's really a multiply by 2,
-        and that's just a left shift of 1.  */
+      /* If we are adding a value to itself, that's really a multiply by 2,
+        and that's just a left shift by 1.  If subtracting, it's just 0.  */
       if (rtx_equal_p (operands[1], operands[2]))
        {
-         gcc_assert (code != MINUS);
-         emit_insn (gen_ashldi3 (operands[0], operands[1], const1_rtx));
+         if (code == PLUS)
+           emit_insn (gen_ashldi3 (operands[0], operands[1], const1_rtx));
+         else
+           emit_move_insn (operands[0], const0_rtx);
          return;
        }