[PATCH] ARM fixed-point support [1/6]: comparison optab biasing

[PATCH] ARM fixed-point support [1/6]: comparison optab biasing

[Julian Brown]

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As per Joseph's suggestion here:

http://gcc.gnu.org/ml/gcc-patches/2011-05/msg00846.html

I am re-posting machine-independent parts of my ARM fixed-point support
patches, with explanations as to why each part is necessary.

This is the first: on ARM, TARGET_LIB_INT_CMP_BIASED is false for
TARGET_BPABI targets (i.e. most currently-interesting cases --
EABI comparison helper functions return -1/0/1 for lt/eq/gt rather than
0/1/2). However the fixed-point helper library uses biased comparisons
unconditionally. So, this patch just makes comparisons between
fixed-point quantities use the biasing rather than not. (Grepping
config/, in practice, this will only affect ARM.)

Tested in a series with other fixed-point patches. OK to apply?

Julian

ChangeLog

    gcc/
    * optabs.c (prepare_cmp_insn): Use correct biasing for fixed-point
    comparison helpers.

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commit 12efebd5f56358c2d194659570ad05e089bbaaf3
Author: Julian Brown <julian@henry8.codesourcery.com>
Date:   Fri May 13 05:42:15 2011 -0700

    Correct biasing for fixed-point optabs.

diff --git a/gcc/optabs.c b/gcc/optabs.c
index 62e123b..a1b85b8 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -3930,11 +3930,13 @@ prepare_cmp_insn (rtx x, rtx y, enum rtx_code comparison, rtx size,
 	 result against 1 in the biased case, and zero in the unbiased
 	 case. For unsigned comparisons always compare against 1 after
 	 biasing the unbiased result by adding 1. This gives us a way to
-	 represent LTU. */
+	 represent LTU.
+	 The comparisons in the fixed-point helper library are always
+	 biased.  */
       x = result;
       y = const1_rtx;
 
-      if (!TARGET_LIB_INT_CMP_BIASED)
+      if (!TARGET_LIB_INT_CMP_BIASED && !ALL_FIXED_POINT_MODE_P (mode))
 	{
 	  if (unsignedp)
 	    x = plus_constant (result, 1);

Re: [PATCH] ARM fixed-point support [1/6]: comparison optab biasing

[Richard Earnshaw]

On 13/05/11 14:57, Julian Brown wrote:
> As per Joseph's suggestion here:
> 
> http://gcc.gnu.org/ml/gcc-patches/2011-05/msg00846.html
> 
> I am re-posting machine-independent parts of my ARM fixed-point support
> patches, with explanations as to why each part is necessary.
> 
> This is the first: on ARM, TARGET_LIB_INT_CMP_BIASED is false for
> TARGET_BPABI targets (i.e. most currently-interesting cases --
> EABI comparison helper functions return -1/0/1 for lt/eq/gt rather than
> 0/1/2). However the fixed-point helper library uses biased comparisons
> unconditionally. So, this patch just makes comparisons between
> fixed-point quantities use the biasing rather than not. (Grepping
> config/, in practice, this will only affect ARM.)
> 
> Tested in a series with other fixed-point patches. OK to apply?
> 
> Julian
> 
> ChangeLog
> 
>     gcc/
>     * optabs.c (prepare_cmp_insn): Use correct biasing for fixed-point
>     comparison helpers.
> 

OK.

R.