Jonas Maebe wrote: >> The recursive call is usually inside an if anyways so the ssa >> optimizer is lost >> anyways, no? > > For the part inside the if: yes. But not for the part coming before it. > What's more important however is that goto/label not only removes the > usage of SSA, it also means that all register variables are allocated at > the start of the function and only freed at the end. Without goto/label, > register variables are only allocated between their first and last use > (usage in a loop means allocation until the end of that loop).
Practical argument: the assembler code _is_ better for the code I tested and up to as twice as fast as the original one. Theoretical argument: - using the tail goto you've one function with one set of variables being active across the the whole function - using a recursive call you've at least two sets of variables: the caller and the callee ones. Though one set is only active at a limited part of the function, the set of the caller is still in use while the callee is called though they (the caller variables) are spilled. > >> BTW: Does the assembler optimizer track flag usage? Then we could >> remove some of >> the >> >> movl %esi,%eax >> incl %eax >> >> like pairs. > > There's a FlagsUsed field in the ttaiprop record which is set to true if > the flags result of that instruction is used. I guess it could be used to change to code above to leal 1(%esi),%eax ? Or is this slower on some CPUs? _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
