Re: [PATCH] bitintlower: Fix memmove source operand in finish_arith_overflow [PR126939]

On 19/08/26 8:42 pm, Jakub Jelinek wrote:
> On Wed, Aug 19, 2026 at 07:29:05AM -0500, Manjunath S Matti wrote:
>> Bootstrapped and regression tested on powerpc64-linux (-m32/-m64), s390 and
>> powerpc64le-linux.
>>
>> finish_arith_overflow builds a memmove call to shift the result of a
>> double-width multiplication down inside the destination object, on
>> big-endian targets where the computed value occupies more limbs than
>> the destination.
>>
>> The destination argument correctly takes the address of OBJ, but SRC is
>> a MEM_REF, that is a value of array type, and it is passed directly as
>> memmove's second argument, which is a pointer.  Wrap it in
>> build_fold_addr_expr so that the address is passed instead.  Since
>> build_fold_addr_expr of a MEM_REF folds back to the pointer, no
>> dereference is materialised.
>>
>> The affected code is guarded by bitint_big_endian, and is only reached
>> for widths whose value needs more limbs than the destination object,
>> that is huge _BitInt operands of __builtin_{add,sub,mul}_overflow, so
>> it needs a big-endian target with _BitInt support to be exercised at
>> all.  It is being hit now that _BitInt is being enabled for powerpc
>> (PR117584).
>>
>> Existing coverage is sufficient: on powerpc64 big-endian this fixes
>> gcc.dg/torture/bitint-93.c and bitint-94.c at -O0 and -O2, and
>> gcc.dg/torture/bitint-32.c through bitint-37.c at -O0.  No new test is
>> added.
>>
>> 2026-08-19  Manjunath Matti  <[email protected]>
>>
>> PR middle-end/126939
> This PR line should be also indented by a tab.
> Otherwise LGTM, I don't see you in write approval, shall I commit this
> for you?

Yes you can commit the patch, but.

Should I resubmit the patch, with the indentation changes ?


>
>> gcc/
>> 	* gimple-lower-bitint.cc (bitint_large_huge::finish_arith_overflow):
>> 	Take the address of the memmove source operand.
>>
>> diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
>> index 52d0acad249..e36534ba13d 100644
>> --- a/gcc/gimple-lower-bitint.cc
>> +++ b/gcc/gimple-lower-bitint.cc
>> @@ -4594,8 +4594,9 @@ bitint_large_huge::finish_arith_overflow (tree var, tree obj, tree type,
>>   			     build_fold_addr_expr (unshare_expr (obj)), off);
>>   	  g = gimple_build_call (fn, 3,
>>   				 build_fold_addr_expr (unshare_expr (obj)),
>> -				 src, build_int_cst (size_type_node,
>> -						     obj_nelts * m_limb_size));
>> +				 build_fold_addr_expr (src),
>> +				 build_int_cst (size_type_node,
>> +						obj_nelts * m_limb_size));
>>   	  insert_before (g);
>>   	}
>>         if (orig_obj == NULL_TREE && obj)
>> -- 
>> 2.52.0
> 	Jakub
>