[PATCH, ifcvt] Check size cost in noce_try_store_flag_mask

[Zhenqiang Chen]

Hi,

Function noce_try_store_flag_mask converts "if (test) x = 0;" to "x &=
-(test == 0);"

But from code size view, "x &= -(test == 0);" might have more instructions
than "if (test) x = 0;". The patch checks the cost to determine the
conversion is valuable or not.

Bootstrap and no make check regression on X86-64.
No make check regression with Cortex-M0 qemu.
For CSiBE, ARM Cortex-m0 result is a little better. A little regression for
MIPS. Roughly no change for PowerPC.

OK for trunk?

Thanks!
-Zhenqiang

ChangeLog:
2014-10-27  Zhenqiang Chen  <zhenqiang.c...@arm.com>

        * ifcvt.c (noce_try_store_flag_mask): Check rtx cost.

testsuite/ChangeLog:
2014-10-27  Zhenqiang Chen  <zhenqiang.c...@arm.com>

        * gcc.target/arm/ifcvt-size-check.c: New test.

diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index 949d2b4..3abd518 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -1393,6 +1393,14 @@ noce_try_store_flag_mask (struct noce_if_info
*if_info)
          if (!seq)
            return FALSE;
 
+         if (optimize_function_for_size_p (cfun))
+           {
+             int old_cost = COSTS_N_INSNS (if_info->branch_cost + 1);
+             int new_cost = seq_cost (seq, 0);
+             if (new_cost > old_cost)
+               return FALSE;
+           }
+
          emit_insn_before_setloc (seq, if_info->jump,
                                   INSN_LOCATION (if_info->insn_a));
          return TRUE;
diff --git a/gcc/testsuite/gcc.target/arm/ifcvt-size-check.c
b/gcc/testsuite/gcc.target/arm/ifcvt-size-check.c
new file mode 100644
index 0000000..43fa16b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/ifcvt-size-check.c
@@ -0,0 +1,13 @@
+/* { dg-do assemble } */
+/* { dg-options "-mthumb -Os " }  */
+/* { dg-require-effective-target arm_thumb1_ok } */
+
+int
+test (unsigned char iov_len, int count, int i)
+{
+  unsigned char bytes = 0;
+  if ((unsigned char) ((char) 127 - bytes) < iov_len)
+    return 22;
+  return 0;
+}
+/* { dg-final { object-size text <= 12 } } */