[PATCH] D74144: [OPENMP50]Add basic support for array-shaping operation.

[Chi Chun Chen via Phabricator via cfe-commits]

cchen added a comment.

In D74144#2307494 <https://reviews.llvm.org/D74144#2307494>, @ABataev wrote:

> In D74144#2307454 <https://reviews.llvm.org/D74144#2307454>, @cchen wrote:
>
>> @ABataev, the below test is extracted from Sollve test suite and Clang now emit:
>>
>>   test.c:17:35: error: subscripted value is not an array or pointer
>>       #pragma omp target update to( (([N][N])foo)[1:M] )
>>                                     ^~~~~~~~~~~~~
>>   test.c:17:5: error: expected at least one 'to' clause or 'from' clause specified to '#pragma omp target update'
>>       #pragma omp target update to( (([N][N])foo)[1:M] )
>>
>> This error message came from the `ActOnOMPArraySectionExpr` which is called inside `ParsePostfixExpressionSuffix`. The issue is that the base expression in `ActOnOMPArraySectionExpr` looks like:
>>
>>   ParenExpr 0x122859be0 '<OpenMP array shaping type>' lvalue
>>   `-OMPArrayShapingExpr 0x122859b98 '<OpenMP array shaping type>' lvalue
>>     |-IntegerLiteral 0x122859b38 'int' 5
>>     |-IntegerLiteral 0x122859b58 'int' 5
>>     `-DeclRefExpr 0x122859b78 'int *' lvalue Var 0x1228599d0 'foo' 'int *'
>>
>> which is not a base that we would expect in an array section expr. I've tried relaxing the base type check in `ActOnOMPArraySectionExpr` but not sure it's the way to go. (or should I just extract the DeclReExpr from ArrayShapingExpr before calling `ActOnOMPArraySectionExpr`?)
>>
>>   #define N 5
>>   #define M 3
>>   
>>   int main(void) {
>>       int tmp[N][N];
>>       for(int i=0; i<N; i++)
>>           for(int j=0; j<N; j++)
>>               tmp[i][j] = N*i + j;
>>   
>>       int *foo = &tmp[0][0];
>>   
>>       // This compiles just fine
>>       //#pragma omp target update to( ([N][N])foo )
>>   
>>       // This is rejected by the compiler
>>       #pragma omp target update to( (([N][N])foo)[1:M] )
>>   }
>
> I don't think it is allowed by the standard.
>
> According to the standard, The shape-operator can appear only in clauses where it is explicitly allowed.
> In this case, array shaping is used as a base expression of array section (or subscript) expression, which does not meet the standard. Tje array sjaping operation is not used in clause, instead it is used as a base subexpression of another expression.

In OpenMP 5.0 [2.12.6, target update construct, Restrictions, C/C++, p.1] The list items that appear in the to or from clauses may use shape-operators.
Also, in the array shaping section in https://github.com/OpenMP/Examples, the example is also illustrated with the same usage:

  ...
  S-17 // update boundary points (two columns of 2D array) on the host
  S-18 // pointer is shaped to 2D array using the shape-operator
  S-19 #pragma omp target update from( (([nx][ny+2])a)[0:nx][1], (([nx][ny+2])a)[0:nx][ny] )
  ...


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