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Re: [PATCH] Fix PR37053: Move tweaks of commutative precedence to target hook

Paolo Bonzini wrote:


I cannot say I like Maxim's patch and he knows, but unfortunately, m68k apparently implements 2-address arithmetic in a different way than x86 (or with other constraint) and we're talking about a lot of ICEs there. :-(

Another possibility, which you would have to try on PowerPC, could be to limit the change of precedence to before reload.

Here is the other patch. It has a downside that *during* and after reload the optimal for PowerPC commutativeness is not available, so that may degrade performance.

Peter, if you find out that this patch doesn't cause any performance problems, I'm happy to go with it.

Index: gcc-mainline/gcc/rtlanal.c
--- gcc-mainline/gcc/rtlanal.c  (revision 148831)
+++ gcc-mainline/gcc/rtlanal.c  (working copy)
@@ -2936,8 +2936,9 @@ commutative_operand_precedence (rtx op)
     case RTX_OBJ:
       /* Complex expressions should be the first, so decrease priority
          of objects.  Prefer pointer objects over non pointer objects.  */
-      if ((REG_P (op) && REG_POINTER (op))
-         || (MEM_P (op) && MEM_POINTER (op)))
+      if ((!reload_completed && !reload_in_progress)
+         && ((REG_P (op) && REG_POINTER (op))
+             || (MEM_P (op) && MEM_POINTER (op))))
        return -1;
       return -2;

That would be a simpler patch and one that does not risk slowing down the compiler that tiny 0.1% that sums up quickly. But it would also be pretty magical...

That's just a check for a global variable to be NULL on most platforms; btw, the above patch checks two global variables ;). On PowerPC the extra work is justified with performance boost.


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