21.6.4 Transforming Block IF

Consider:

     SUBROUTINE X(A,B,C)
     CHARACTER*(*) A, B, C
     LOGICAL LFUNC
     
     IF (LFUNC (A//B)) THEN
       CALL SUBR1
     ELSE IF (LFUNC (A//C)) THEN
       CALL SUBR2
     ELSE
       CALL SUBR3
     END

The arguments to the two calls to `LFUNC' require dynamic allocation (at run time), but are not required during execution of the CALL statements.

So, the scopes of those temporaries must be within blocks inside the block corresponding to the Fortran IF block.

This cannot be represented “naturally” in vanilla C, nor in GBEL. The if, elseif, else, and endif constructs provided by both languages must, for a given if block, share the same C/GBE block.

Therefore, any temporaries needed during evaluation of `expr' while executing `ELSE IF(expr)' must either have been predeclared at the top of the corresponding IF block, or declared within a new block for that ELSE IF—a block that, since it cannot contain the else or else if itself (due to the above requirement), actually implements the rest of the IF block's ELSE IF and ELSE statements within an inner block.

The FFE takes the latter approach.