On Tue, 25 May 2010 16:28:37 +0800, "Amker.Cheng" wrote: > Hi all, > I compared assembly files of a function compiled by GCC4.3.4 and > GCC3.4.4. > The function focuses on array computation and has no branch, or any > loop structure, > The command line is like "-march=mips32r2 -O3", and here is the > instruction statics: > > total : 1879 : 1534 > addiu : 6 : 6 > addu : 216 : 129 > jr : 1 : 1 > lui : 5 : 5 > lw : 396 : 353 > madd : 41 : 0 > mfhi : 80 : 80 > mflo : 121 : 86 > move : 0 : 21 > mtlo : 39 : 0 > mul : 85 : 0 > mult : 18 : 80 > multu : 64 : 0 > or : 80 : 80 > sll : 80 : 80 > sra : 79 : 47 > srl : 80 : 80 > subu : 80 : 80 > sw : 408 : 406 > > Considering there is no any branch or loop structure ,It seems result > of GCC3.4.4 > is much better, since generating much less instructions. > > secondly, GCC4.3.4 does consume less stack slots(1224 bytes against 1408). > > So, any comments? Thanks in advance. Posting some random numbers without a test-case and precise command line parameters for both compilers makes the numbers useless, IMHO. You also only mention instruction counts. Have you actually benchmarked the resulting code? CPUs are complicated and what you might perceive as worse code might actually be superior thanks to scheduling and internal CPU parallelism etc.
-- VH
