Re: [PATCH][ARM][1/4] Replace uses of int_log2 by exact_log2

[Kyrill Tkachov]

I wanted to ping this patch, but checking the gcc-patches archive I see this 
wasn't
archived, though I have confirmed that the patch was sent out and distributed by
the mail server correctly.

Anyway, resending...

Thanks,
Kyrill

On 24/05/16 14:25, Kyrill Tkachov wrote:

Hi all,

The int_log2 function in arm.c is not really useful since we already have a 
generic function for calculating
the log2 of HOST_WIDE_INTs. The only difference in functionality is that 
int_log2 also asserts that the result
is no greater than 31.

This patch removes int_log2 in favour of exact_log2 and adds an assert on the 
result to make sure the return
value was as expected.

Bootstrapped and tested on arm-none-linux-gnueabihf.

Is this ok? Or is there something I'm missing about int_log2?

Thanks,
Kyrill

2016-05-24  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>

    * config/arm/arm.c (int_log2): Delete definition and prototype.
    (shift_op): Use exact_log2 instead of int_log2.
    (vfp3_const_double_for_fract_bits): Likewise.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 6cc0feb6f87157171c889e998e52b4e5d8683c66..3fe6eab46f3c18ace6899b5be45ad646992f43e4 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -104,7 +104,6 @@ static void arm_print_operand_address (FILE *, machine_mode, rtx);
 static bool arm_print_operand_punct_valid_p (unsigned char code);
 static const char *fp_const_from_val (REAL_VALUE_TYPE *);
 static arm_cc get_arm_condition_code (rtx);
-static HOST_WIDE_INT int_log2 (HOST_WIDE_INT);
 static const char *output_multi_immediate (rtx *, const char *, const char *,
 					   int, HOST_WIDE_INT);
 static const char *shift_op (rtx, HOST_WIDE_INT *);
@@ -18920,7 +18919,8 @@ shift_op (rtx op, HOST_WIDE_INT *amountp)
 	  return NULL;
 	}
 
-      *amountp = int_log2 (*amountp);
+      *amountp = exact_log2 (*amountp);
+      gcc_assert (IN_RANGE (*amountp, 0, 31));
       return ARM_LSL_NAME;
 
     default:
@@ -18952,22 +18952,6 @@ shift_op (rtx op, HOST_WIDE_INT *amountp)
   return mnem;
 }
 
-/* Obtain the shift from the POWER of two.  */
-
-static HOST_WIDE_INT
-int_log2 (HOST_WIDE_INT power)
-{
-  HOST_WIDE_INT shift = 0;
-
-  while ((((HOST_WIDE_INT) 1 << shift) & power) == 0)
-    {
-      gcc_assert (shift <= 31);
-      shift++;
-    }
-
-  return shift;
-}
-
 /* Output a .ascii pseudo-op, keeping track of lengths.  This is
    because /bin/as is horribly restrictive.  The judgement about
    whether or not each character is 'printable' (and can be output as
@@ -27691,7 +27675,11 @@ vfp3_const_double_for_fract_bits (rtx operand)
 	  HOST_WIDE_INT value = real_to_integer (&r0);
 	  value = value & 0xffffffff;
 	  if ((value != 0) && ( (value & (value - 1)) == 0))
-	    return int_log2 (value);
+	    {
+	      int ret = exact_log2 (value);
+	      gcc_assert (IN_RANGE (ret, 0, 31));
+	      return ret;
+	    }
 	}
     }
   return 0;