regalloc: improve spilling and cleanup

Instead of spilling current interval when running out of registers,
spill the longest-lived active interval with a lower spill cost than
current. Spill costs are estimated based on multiplicative loop depth.
Also cleanup regalloc.c somewhat.
Update todo.txt too.

1 files changed, 2 insertions, 1 deletions

diff --git a/ir/ir.c b/ir/ir.c
index 626311e..b612143 100644
--- a/ir/ir.c
+++ b/ir/ir.c
@@ -479,7 +479,7 @@ insertphi(struct block *blk, enum irclass cls)
    return mkref(RTMP, new);
 }
 
-void
+uint
 numberinstrs(struct function *fn)
 {
    struct block *blk = fn->entry;
@@ -488,6 +488,7 @@ numberinstrs(struct function *fn)
       blk->inumstart = start;
       start += blk->ins.n+2;
    } while ((blk = blk->lnext) != fn->entry);
+   return start-1;
 }
 
 static bool