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| author | Quentin Carbonneaux <quentin@c9x.me> | 2022-12-18 17:35:19 +0100 |
|---|---|---|
| committer | Quentin Carbonneaux <quentin@c9x.me> | 2022-12-25 16:37:33 +0100 |
| commit | 5e9726946dcb9248dbd34ded1bdd4f7af8dc2d31 (patch) | |
| tree | 9842f9837784911e386357af18b08a2ca1b69896 /fold.c | |
| parent | c5cd65261e05029889450ca27050785504164853 (diff) | |
| download | roux-5e9726946dcb9248dbd34ded1bdd4f7af8dc2d31.tar.gz | |
new UNDEF Ref
Crashing loads of uninitialized memory proved to be a problem when implementing unions using qbe. This patch introduces a new UNDEF Ref to represent data that is known to be uninitialized. Optimization passes can make use of it to eliminate some code. In the last compilation stages, UNDEF is treated as the constant 0xdeaddead.
Diffstat (limited to 'fold.c')
| -rw-r--r-- | fold.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/fold.c b/fold.c index f992b3a..3ff0bc7 100644 --- a/fold.c +++ b/fold.c @@ -1,8 +1,8 @@ #include "all.h" enum { - Bot = -2, /* lattice bottom */ - Top = -1, /* lattice top */ + Bot = -1, /* lattice bottom */ + Top = 0, /* lattice top (matches UNDEF) */ }; typedef struct Edge Edge; @@ -126,7 +126,6 @@ visitjmp(Blk *b, int n, Fn *fn) switch (b->jmp.type) { case Jjnz: l = latval(b->jmp.arg); - assert(l != Top && "ssa invariant broken"); if (l == Bot) { edge[n][1].work = flowrk; edge[n][0].work = &edge[n][1]; @@ -174,7 +173,6 @@ renref(Ref *r) if (rtype(*r) == RTmp) if ((l=val[r->val]) != Bot) { - assert(l != Top && "ssa invariant broken"); *r = CON(l); return 1; } @@ -294,9 +292,13 @@ fold(Fn *fn) for (i=b->ins; i<&b->ins[b->nins]; i++) if (renref(&i->to)) *i = (Ins){.op = Onop}; - else + else { for (n=0; n<2; n++) renref(&i->arg[n]); + if (isstore(i->op)) + if (req(i->arg[0], UNDEF)) + *i = (Ins){.op = Onop}; + } renref(&b->jmp.arg); if (b->jmp.type == Jjnz && rtype(b->jmp.arg) == RCon) { if (iscon(&fn->con[b->jmp.arg.val], 0, 0)) { |