On Wed, 23 Feb 2005, James E Wilson wrote:
Tarun Kawatra wrote:^^^^^^^^^^^^^^^^^^^^^^^During expression hash table construction in gcse pass(gcc vercion 3.4.1), expressions like a*b does not get included into the expression hash table. Such expressions occur in PARALLEL along with clobbers.
You didn't mention the target, or exactly what the mult looks like.
However, this isn't hard to answer just by using the source. hash_scan_set calls want_to_cse_p calls can_assign_to_reg_p calls added_clobbers_hard_reg_p which presumably returns true, which prevents the optimization. This makes sense. If the pattern clobbers a hard reg, then we can't safely insert it at any place in the function. It might be clobbering the hard reg at a point where it holds a useful value.
While looking at this, I noticed can_assign_to_reg_p does something silly.
I could not find this function anywhere in gcc 3.4.1 source. Although FIRST_PSEUDO_REGISTER * 2 is being used in make_insn_raw in want_to_gcse_p directly as follows
if (test_insn == 0)
{
test_insn = make_insn_raw (gen_rtx_SET (VOIDmode, gen_rtx_REG (word_mode,
FIRST_PSEUDO_REGISTER * 2), const0_rtx));
NEXT_INSN (test_insn) = PREV_INSN (test_insn) = 0;
}It uses "FIRST_PSEUDO_REGISTER * 2" to try to generate a test pseudo register, but this can fail if a target has less than 4 registers, or if the set of virtual registers increases in the future. This should probably be LAST_VIRTUAL_REGISTER + 1 as used in another recent patch.
I could not get this point.
-tarun
