backend: fix mem2reg & regalloc

they were broken, especially for unstructured control flow. most
significant fix is to register allocator for temporaries that are used
before the first definition in the source order, e.g.:

    @1:
        %x = add %y, 1
        b @3
    @2
        %y = ...
        b @1

it's legal for %x to use %y there (assuming @2 dominates @1) but from
the point of view of the register allocator %y is defined and freed
and then used again, which broke things. the fix is to introduce phis
for this situation:

    @1:
        %y.1 = phi @2 %y
        %x = add %y.1, 1
        b @3
    @2
        %y = ...
        b @1

then regalloc phi handling code makes it work

1 files changed, 1 insertions, 0 deletions

diff --git a/main.c b/main.c
index 6f9e0dc..35d25ac 100644
--- a/main.c
+++ b/main.c
@@ -116,6 +116,7 @@ optparse(char **args)
          case 'p': ccopt.dbg.p = 1; break;
          case 'a': ccopt.dbg.a = 1; break;
          case 'i': ccopt.dbg.i = 1; break;
+         case 'l': ccopt.dbg.l = 1; break;
          case 'r': ccopt.dbg.r = 1; break;
          case 'm': ccopt.dbg.m = 1; break;
          default: warn(NULL, "-d: invalid debug flag %'c", *arg);