[PATCH][tree-ssa-address] Use simplify_gen_binary in gen_addr_rtx

[Kyrill Tkachov]

Hi all,

The testcase in this patch generates bogus assembly for arm with -O1 
-mfloat-abi=soft:
       strd    r4, [#0, r3]

This is due to non-canonical RTL being generated during expansion:
(set (mem:DI (plus:SI (const_int 0 [0])
                (reg/f:SI 153)) [0 MEM[symbol: a, index: _26, offset: 0B]+0 S8 
A64])
        (reg:DI 154))

Note the (plus (const_int 0) (reg)). This is being generated in gen_addr_rtx in 
tree-ssa-address.c
where it creates an explicit PLUS rtx through gen_rtx_PLUS, which doesn't try 
to canonicalise its arguments
or simplify. The correct thing to do is to use simplify_gen_binary that will 
handle all this properly.

I didn't change the other gen_rtx_PLUS calls in this function as their results 
is later used in XEXP operations
that seem to rely on a PLUS expression being explicitly produced, but this 
particular call doesn't, so it's okay
to change it. With this patch the sane assembly is generated:
        strd    r4, [r3]

Bootstrapped and tested on arm-none-linux-gnueabihf, x86_64, 
aarch64-none-linux-gnu.

Ok for trunk?

Thanks,
Kyrill

2016-12-20  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>

    * tree-ssa-address.c (gen_addr_rtx): Use simplify_gen_binary to add
    *addr to act_elem.

2016-12-20  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>

    * gcc.dg/20161219.c: New test.

diff --git a/gcc/testsuite/gcc.dg/20161219.c b/gcc/testsuite/gcc.dg/20161219.c
new file mode 100644
index 0000000000000000000000000000000000000000..93ea8d2364d9ab54704a84e6c0bff0427df82db8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/20161219.c
@@ -0,0 +1,30 @@
+/* { dg-do assemble } */
+/* { dg-options "-O1 -w" } */
+
+static long long a[9];
+int b, c, d, e, g;
+
+static int
+fn1 (int *p1)
+{
+  b = 1;
+  for (; b >= 0; b--)
+    {
+      d = 0;
+      for (;; d++)
+	{
+	  e && (a[d] = 0);
+	  if (*p1)
+	    break;
+	  c = (int) a;
+	}
+    }
+  return 0;
+}
+
+int
+main ()
+{
+  int f = fn1 ((int *) f);
+  return f;
+}
diff --git a/gcc/tree-ssa-address.c b/gcc/tree-ssa-address.c
index a53ade0600d01c9d48f6c789b78fd42d7a06a95b..0c7c5902cebb0196c8e27f4eba45ce176cc3f0a5 100644
--- a/gcc/tree-ssa-address.c
+++ b/gcc/tree-ssa-address.c
@@ -154,7 +154,7 @@ gen_addr_rtx (machine_mode address_mode,
 	}
 
       if (*addr)
-	*addr = gen_rtx_PLUS (address_mode, *addr, act_elem);
+	*addr = simplify_gen_binary (PLUS, address_mode, *addr, act_elem);
       else
 	*addr = act_elem;
     }