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/*
* UnSSA - translate the SSA back to normal form.
*
* For now it's done by replacing to set of copies:
* 1) For each phi-node, replace all their phisrc by copies to a common
* temporary.
* 2) Replace all the phi-nodes by copies of the temporaries to the phi-node target.
* This is node to preserve the semantic of the phi-node (they should all "execute"
* simultaneously on entry in the basic block in which they belong).
*
* This is similar to the "Sreedhar method I" except that the copies to the
* temporaries are not placed at the end of the predecessor basic blocks, but
* at the place where the phi-node operands are defined (the same place where the
* phisrc were present).
* Is this a problem?
*
* While very simple this method create a lot more copies that really necessary.
* Ideally, "Sreedhar method III" should be used:
* "Translating Out of Static Single Assignment Form", V. C. Sreedhar, R. D.-C. Ju,
* D. M. Gillies and V. Santhanam. SAS'99, Vol. 1694 of Lecture Notes in Computer
* Science, Springer-Verlag, pp. 194-210, 1999.
*
* Copyright (C) 2005 Luc Van Oostenryck
*/
#include "lib.h"
#include "linearize.h"
#include "allocate.h"
#include <assert.h>
static struct instruction *alloc_copy_insn(struct instruction *phisrc)
{
struct instruction *insn = __alloc_instruction(0);
insn->opcode = OP_COPY;
insn->size = phisrc->size;
insn->pos = phisrc->pos;
return insn;
}
// Is there a better way to do this ???
static void insert_insn_before(struct instruction *old, struct instruction *new)
{
struct instruction *insn;
FOR_EACH_PTR_REVERSE(old->bb->insns, insn) {
if (insn == old)
INSERT_CURRENT(new, insn);
}
END_FOR_EACH_PTR_REVERSE(insn);
}
static void insert_copy(struct instruction *phisrc, pseudo_t tmp)
{
struct instruction *cpy;
assert(phisrc->opcode == OP_PHISOURCE);
cpy = alloc_copy_insn(phisrc);
cpy->target = tmp;
cpy->src = phisrc->phi_src;
cpy->bb = phisrc->bb;
insert_insn_before(phisrc, cpy);
}
static void copy_phi_args(struct instruction *phi, struct pseudo_list **list)
{
pseudo_t tmp, orig = phi->target;
pseudo_t phisrc;
tmp = alloc_pseudo(NULL);
tmp->type = orig->type;
tmp->def = phi; // wrongly set to the phi-node !!!
// but used later
add_pseudo(list, tmp);
FOR_EACH_PTR(phi->phi_list, phisrc) {
if (!phisrc->def)
continue;
insert_copy(phisrc->def, tmp);
} END_FOR_EACH_PTR(phisrc);
}
static void unssa_bb(struct basic_block *bb)
{
struct pseudo_list *list = NULL;
struct pseudo *tmp;
struct instruction *insn;
// copy all the phi nodes arguments to a new temporary pseudo
FOR_EACH_PTR(bb->insns, insn) {
if (insn->opcode != OP_PHI)
continue;
copy_phi_args(insn, &list);
} END_FOR_EACH_PTR(insn);
// now replace all the phi nodes themselves by copies of the
// temporaries to the phi nodes targets
FOR_EACH_PTR(list, tmp) {
struct instruction *phi = tmp->def;
phi->opcode = OP_COPY;
phi->src = tmp;
} END_FOR_EACH_PTR(tmp);
free_ptr_list(&list);
}
int unssa(struct entrypoint *ep)
{
struct basic_block *bb;
FOR_EACH_PTR(ep->bbs, bb) {
unssa_bb(bb);
} END_FOR_EACH_PTR(bb);
return 0;
}
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