This directive associates an alignment attribute with a symbol definition for a register offset. You can use this directive when you know the alignment of the base register. This attribute guarantees to the compiler that the base register has the same alignment, which enables the compiler to generate optimal code. Format .SYMBOL_ALIGNMENT argument-list
1 – Parameters
argument-list One of the arguments listed in the following table: Option Description long Declares longword alignment for any symbol that you declare after this directive. quad Declares quadword alignment for any symbol that you declare after this directive. none Turns off the alignment specified by the preceding .SYMBOL_ALIGNMENT directive.
2 – Description
The .SYMBOL_ALIGNMENT directive is used to associate an alignment attribute with the fields in a structure when you know the base alignment. It is used in pairs. The first .SYMBOL_ALIGNMENT directive associates either longword (long) or quadword (quad) alignment with the symbol or symbols that follow. The second directive, .SYMBOL_ALIGNMENT none, turns it off. Any time a reference is made with a symbol with an alignment attribute, the base register of that reference, in effect, inherits the symbol's alignment. The compiler also resets the base register's alignment to longword for subsequent alignment tracking. This alignment guarantee enables the compiler to produce more efficient code sequences.
3 – Example
OFFSET1 = 4 .SYMBOL_ALIGNMENT LONG OFFSET2 = 8 OFFSET3 = 12 .SYMBOL_ALIGNMENT QUAD OFFSET4 = 16 .SYMBOL_ALIGNMENT NONE OFFSET5 = 20 . . . CLR1 OFFSET2(R8) . . . MOVL R2, OFFSET4(R6) For OFFSET1 and OFFSET5, the compiler will use only its tracking information for deciding if Rn in OFFSET1(Rn) is aligned or not. For the other references, the base register will be treated as longword (OFFSET2 and OFFSET3) or quadword (OFFSET4) aligned. After each use of OFFSET2 or OFFSET4, the base register in the reference is reset to longword alignment. In this example, the alignment of R8 and R6 will be reset to longword, although the reference to OFFSET4 will use the stronger quadword alignment.