Intel® 64 and IA-32 Architectures Optimization Reference Manual

GENERAL OPTIMIZATION GUIDELINES3.5.4.3 Stack OptimizationIn Example 3-22, an input parameter was copied in turn onto the stack and passedto the non-vectorizable routine for processing. The parameter passing from consecutivememory locations can be simplified by a technique shown in Example 3-25.Example 3-25. Stack Optimization Technique to Simplify Parameter Passingcall foomov [ebp+16], eaxadd ebp, 4call foomov [ebp+16], eaxadd ebp, 4call foomov [ebp+16], eaxadd ebp, 4call fooStack Optimization can only be used when:• The serial operations are function calls. The function “foo” is declared as: INTFOO(INT A). The parameter is passed on the stack.• The order of operation on the components is from last to first.Note the call to FOO and the advance of EDP when passing the vector elements toFOO one by one from last to first.3.5.4.4 Tuning ConsiderationsTuning considerations for situations represented by looping of Example 3-22 include• Applying one of more of the following combinations:— choose an alternate packing technique— consider a technique to simply result-passing— consider the stack optimization technique to simplify parameter passing• Minimizing the average number of cycles to execute one iteration of the loop• Minimizing the per-iteration cost of the unpacking and packing operationsThe speed improvement by using the techniques discussed in this section will vary,depending on the choice of combinations implemented and characteristics of thenon-vectorizable routine. For example, if the routine “foo” is short (representative of3-44