Re: Fix pessimistic DImode handling in combine.c:make_field_assignment

[Richard Sandiford <richard.sandiford@linaro.org>]

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Richard Sandiford <richard.sandiford@linaro.org> writes:
> Richard Sandiford <richard.sandiford@linaro.org> writes:
>> The make_field_assignment code:
>>
>>       src = force_to_mode (src, mode,
>> 		       GET_MODE_PRECISION (mode) >= HOST_BITS_PER_WIDE_INT
>> 		       ? HOST_WIDE_INT_M1U
>> 		       : (HOST_WIDE_INT_1U << len) - 1,
>> 		       0);
>>
>> would ignore the field length len for DImode, even though DImode can be
>> handled using HWIs.  I think the code should be testing len instead.
>>
>> The patch was originally part of the SVE machine_mode series.
>> Retesting showed that it changed the asm output on powerpc for a few
>> tests, so I thought it should go in separately.  Each test change
>> seemed to be an improvement.
>>
>> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  I no longer have
>> access to the compile farm to test on the powerpc boxes there.
>
> Now tested on powerpc64le-linux-gnu too (thanks to Segher for the access).
>
>> Thanks,
>> Richard
>>
>>
>> 2017-05-24  Richard Sandiford  <richard.sandiford@linaro.org>
>>
>> gcc/
>> 	* combine.c (make_field_assignment): Check len rather than the mode
>> 	precision when calling force_to_mode.
>>
>> Index: gcc/combine.c
>> ===================================================================
>> --- gcc/combine.c	2017-05-03 08:46:32.777861592 +0100
>> +++ gcc/combine.c	2017-05-24 09:25:25.170351268 +0100
>> @@ -9634,7 +9634,7 @@ make_field_assignment (rtx x)
>>  						     other, pos),
>>  			       dest);
>>    src = force_to_mode (src, mode,
>> -		       GET_MODE_PRECISION (mode) >= HOST_BITS_PER_WIDE_INT
>> +		       len >= HOST_BITS_PER_WIDE_INT
>>  		       ? HOST_WIDE_INT_M1U
>>  		       : (HOST_WIDE_INT_1U << len) - 1,
>>  		       0);