Hi, I am working on gcc-4.1.1 and Itanium architecture. Current now I
have finished instrumenting ld and st instructions before the second
scheduling pass by reserving two global registers at backend. However,
in order to enhance the performance (e.g. make the scheduling better),
I choose to allocate two registers for each instrumentation instead of
using the reserved ones. To identify which registers I can use for
each ld and st instruction, I follow the following idea:
For each insn, I compute its live-in and live-out by starting from the
basic-block:
as we can get the live-in of the basic-block, then, for INSN(N) in the
basic-block,
(1) live-in[ INSN(N) ] = live-out [ INSN(N-1) ]
(2) live-out[ INSN(N) ] = (live-in [ INSN(N) ] U set)
-(REG_DEAD U REG_UNUSED)
where set is the set of registers set by the insn, and REG_DEAD,
REG_UNUSED can be got from the insn notes.
Then, R-( live-in[INSN(N)] U live-out[INSN(N)] ) is the set of
registers I can use to instrument INSN(N). (here R is a set of
registers I specified, for example, all the caller-save global general
registers)
Am I right? or is there any thing I mis-understand, if any, please
point out, thanks!
Further, how to identify SET in (1) ? I have found many of the insns
just before the second scheduling have only one set in it. If this is
hold for all insns, I think I can use the single_set to get SET. Is
there any exception for that? thanks again
Wu
