expansion of vector shifts...

David Miller davem@davemloft.net
Tue Feb 12 22:31:00 GMT 2013


From: David Miller <davem@redhat.com>
Date: Fri, 16 Nov 2012 00:33:05 -0500 (EST)

> From: Richard Sandiford <rdsandiford@googlemail.com>
> Date: Mon, 29 Oct 2012 10:14:53 +0000
> 
>> ...given that the code is like you say written:
>> 
>>   if (SHIFT_COUNT_TRUNCATED)
>>     {
>>       if (CONST_INT_P (op1)
>>         ...
>>       else if (GET_CODE (op1) == SUBREG
>> 	       && subreg_lowpart_p (op1)
>> 	       && INTEGRAL_MODE_P (GET_MODE (SUBREG_REG (op1))))
>> 	op1 = SUBREG_REG (op1);
>>     }
>> 
>> INTEGRAL_MODE_P (GET_MODE (op1)) might be better than an explicit
>> VECTOR_MODE_P check.  The code really doesn't make sense for anything
>> other than integers.
>> 
>> (It amounts to the same thing in practice, of course...)
> 
> Agreed, I've just committed the following.  Thanks!
> 
> ====================
> Fix gcc.c-torture/compile/pr53410-2.c on sparc.
> 
> 	* expmed.c (expand_shift_1): Don't strip non-integral SUBREGs.

This is broken on sparc again, although I'm confused about how this
has happened.

The suggestion was to use INTEGRAL_MODE_P as the test, so what's there
in expand_shift_1() is:

      else if (GET_CODE (op1) == SUBREG
	       && subreg_lowpart_p (op1)
	       && INTEGRAL_MODE_P (GET_MODE (SUBREG_REG (op1)))
	       && INTEGRAL_MODE_P (GET_MODE (op1)))
	op1 = SUBREG_REG (op1);

but INTEGRAL_MODE_P accepts vectors.  This is really confusing because
I was absolutely sure I re-ran the test case with the fix I committed
and it didn't crash any more.

Maybe what we really mean to do here is check both op1 and SUBREG_REG
(op1) against SCALAR_INT_MODE_P instead of INTEGRAL_MODE_P?

Something like this:

gcc/

2013-02-12  David S. Miller  <davem@davemloft.net>

	* expmed.c (expand_shift_1): Only strip scalar integer subregs.

diff --git a/gcc/expmed.c b/gcc/expmed.c
index 4a6ddb0..954a360 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -2116,8 +2116,8 @@ expand_shift_1 (enum tree_code code, enum machine_mode mode, rtx shifted,
 		       % GET_MODE_BITSIZE (mode));
       else if (GET_CODE (op1) == SUBREG
 	       && subreg_lowpart_p (op1)
-	       && INTEGRAL_MODE_P (GET_MODE (SUBREG_REG (op1)))
-	       && INTEGRAL_MODE_P (GET_MODE (op1)))
+	       && SCALAR_INT_MODE_P (GET_MODE (SUBREG_REG (op1)))
+	       && SCALAR_INT_MODE_P (GET_MODE (op1)))
 	op1 = SUBREG_REG (op1);
     }
 




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