mtag/math: use mtag information
[smatch.git] / unssa.c
blobe7c9154d531a148c23f20030af1cebfceb456001
1 /*
2 * UnSSA - translate the SSA back to normal form.
4 * For now it's done by replacing to set of copies:
5 * 1) For each phi-node, replace all their phisrc by copies to a common
6 * temporary.
7 * 2) Replace all the phi-nodes by copies of the temporaries to the phi-node target.
8 * This is node to preserve the semantic of the phi-node (they should all "execute"
9 * simultaneously on entry in the basic block in which they belong).
11 * This is similar to the "Sreedhar method I" except that the copies to the
12 * temporaries are not placed at the end of the predecessor basic blocks, but
13 * at the place where the phi-node operands are defined.
14 * This is particulary easy since these copies are essentialy already present
15 * as the corresponding OP_PHISOURCE.
17 * While very simple this method create a lot more copies that really necessary.
18 * We eliminate some of these copies but most probably most of them are still
19 * useless.
20 * Ideally, "Sreedhar method III" should be used:
21 * "Translating Out of Static Single Assignment Form", V. C. Sreedhar, R. D.-C. Ju,
22 * D. M. Gillies and V. Santhanam. SAS'99, Vol. 1694 of Lecture Notes in Computer
23 * Science, Springer-Verlag, pp. 194-210, 1999.
24 * But for this we need precise liveness, on each %phi and not only on OP_PHI's
25 * target pseudos.
27 * Copyright (C) 2005 Luc Van Oostenryck
30 #include "lib.h"
31 #include "linearize.h"
32 #include "allocate.h"
33 #include "flow.h"
34 #include <assert.h>
37 static inline int nbr_pseudo_users(pseudo_t p)
39 return ptr_list_size((struct ptr_list *)p->users);
42 static int simplify_phi_node(struct instruction *phi, pseudo_t tmp)
44 pseudo_t target = phi->target;
45 struct pseudo_user *pu;
46 pseudo_t src;
48 // verify if this phi can be simplified
49 FOR_EACH_PTR(phi->phi_list, src) {
50 struct instruction *def = src->def;
52 if (!def)
53 continue;
54 if (def->bb == phi->bb)
55 return 0;
56 } END_FOR_EACH_PTR(src);
58 // no need to make a copy of this one
59 // -> replace the target pseudo by the tmp
60 FOR_EACH_PTR(target->users, pu) {
61 use_pseudo(pu->insn, tmp, pu->userp);
62 } END_FOR_EACH_PTR(pu);
64 phi->bb = NULL;
65 return 1;
68 static void replace_phi_node(struct instruction *phi)
70 pseudo_t tmp;
71 pseudo_t p;
73 tmp = alloc_pseudo(NULL);
74 tmp->type = phi->target->type;
75 tmp->ident = phi->target->ident;
76 tmp->def = NULL; // defined by all the phisrc
78 // can we avoid to make of copy?
79 simplify_phi_node(phi, tmp);
81 // rewrite all it's phi_src to copy to a new tmp
82 FOR_EACH_PTR(phi->phi_list, p) {
83 struct instruction *def = p->def;
84 pseudo_t src;
86 if (p == VOID)
87 continue;
89 assert(def->opcode == OP_PHISOURCE);
91 def->opcode = OP_COPY;
92 def->target = tmp;
94 // can we eliminate the copy?
95 src = def->phi_src;
96 if (src->type != PSEUDO_REG)
97 continue;
98 switch (nbr_pseudo_users(src)) {
99 struct instruction *insn;
100 case 1:
101 insn = src->def;
102 if (!insn)
103 break;
104 insn->target = tmp;
105 case 0:
106 kill_instruction(def);
107 def->bb = NULL;
109 } END_FOR_EACH_PTR(p);
111 if (!phi->bb)
112 return;
114 // rewrite the phi node:
115 // phi %rt, ...
116 // to:
117 // copy %rt, %tmp
118 phi->opcode = OP_COPY;
119 use_pseudo(phi, tmp, &phi->src);
122 static void rewrite_phi_bb(struct basic_block *bb)
124 struct instruction *insn;
126 // Replace all the phi-nodes by copies of a temporary
127 // (which represent the set of all the %phi that feed them).
128 // The target pseudo doesn't change.
129 FOR_EACH_PTR(bb->insns, insn) {
130 if (!insn->bb)
131 continue;
132 if (insn->opcode != OP_PHI)
133 continue;
134 replace_phi_node(insn);
135 } END_FOR_EACH_PTR(insn);
138 int unssa(struct entrypoint *ep)
140 struct basic_block *bb;
142 FOR_EACH_PTR(ep->bbs, bb) {
143 rewrite_phi_bb(bb);
144 } END_FOR_EACH_PTR(bb);
146 return 0;