Hi :
I'm puzzled when looking into speculative scheduling in gcc, the 4.2.4 version.
First, I noticed the document describing IBM haifa instruction
scheduler(as PowerPC Reference Compiler Optimization Project).
It presents that the instruction motion from bb s(dominated by t)
to t is speculative when split_blocks(s, t) not empty.
Second, There is SCED_FLAGS like DO_SPECULATION in codes.
Here goes questions.
1, Does the DO_SPECULATION flag constrol whether do the
mentioned speculative motion or not?
2, For mips target, which has the DO_SPECULATION bit cleared,
gcc still does speculative motion when scheduling(first pass),
so it seems the answer of question 1 is negative, but then
what the DO_SPECULATION flag for?
I must have missed something important, Please help out.
Thanks
--
Best Regards.
