[PATCH] Update check after force_const_mem call in the plus_constant function to see if the value returned is not a NULL_RTX.

[Andrew Bennett]

Hi,

In the plus_constant function in explow.c the code to update a constant pool 
value
does not deal with the case where the value returned from force_const_mem is a 
NULL_RTX.  This occurs for the MIPS target because its 
cannot_force_const_mem target function does not allow constants (so that the 
move expanders can deal with them later on), this then causes the 
force_const_mem 
function to return a NULL_RTX and then causes GCC to segmentation fault when 
calling
the memory_address_p function.

The fix is to add a check that the tem variable is not a NULL_RTX before
the memory_address_p function call.  I have tested the fix on the 
mips-mti-linux-gnu
target for both mips32r2 o32 and mips64r2 n64 and there have been no 
regressions.

The patch and ChangeLog are below.

Ok to commit?


Many thanks,



Andrew



        * explow.c (plus_constant): Update check after force_const_mem call to 
see if the
        value returned is not a NULL_RTX.



diff --git a/gcc/explow.c b/gcc/explow.c
index d1a2bf8..8745aea 100644
--- a/gcc/explow.c
+++ b/gcc/explow.c
@@ -132,7 +132,9 @@ plus_constant (machine_mode mode, rtx x, HOST_WIDE_INT c,
        {
          tem = plus_constant (mode, get_pool_constant (XEXP (x, 0)), c);
          tem = force_const_mem (GET_MODE (x), tem);
-         if (memory_address_p (GET_MODE (tem), XEXP (tem, 0)))
+         /* Targets may disallow some constants in the constant pool, thus
+            force_const_mem may return NULL_RTX.  */
+         if (tem && memory_address_p (GET_MODE (tem), XEXP (tem, 0)))
            return tem;
        }
       break;