diff options
Diffstat (limited to 'lib/msandr/msandr.cc')
| -rw-r--r-- | lib/msandr/msandr.cc | 28 |
1 files changed, 21 insertions, 7 deletions
diff --git a/lib/msandr/msandr.cc b/lib/msandr/msandr.cc index c1faec2e..6c9d7c67 100644 --- a/lib/msandr/msandr.cc +++ b/lib/msandr/msandr.cc @@ -309,17 +309,31 @@ void InstrumentMops(void *drcontext, instrlist_t *bb, instr_t *instr, opnd_t op, opnd_size_t op_size = opnd_get_size(op); CHECK(op_size != OPSZ_NA); uint access_size = opnd_size_in_bytes(op_size); - // TODO: optimize it with check-before-write if (access_size <= 4 || op_size == OPSZ_PTR /* x64 support sign extension */) { - PRE(instr, - mov_st(drcontext, opnd_create_base_disp(R1, DR_REG_NULL, 0, 0, op_size), - opnd_create_immed_int((ptr_int_t) 0, - (op_size == OPSZ_PTR) ? OPSZ_4 : op_size))); + instr_t *label = INSTR_CREATE_label(drcontext); + opnd_t immed; + if (op_size == OPSZ_PTR || op_size == OPSZ_4) + immed = OPND_CREATE_INT32(0); + else + immed = opnd_create_immed_int((ptr_int_t) 0, op_size); + // we check if target is 0 before write to reduce unnecessary memory stores. + PRE(instr, cmp(drcontext, + opnd_create_base_disp(R1, DR_REG_NULL, 0, 0, op_size), + immed)); + PRE(instr, jcc(drcontext, OP_je, opnd_create_instr(label))); + PRE(instr, mov_st(drcontext, + opnd_create_base_disp(R1, DR_REG_NULL, 0, 0, op_size), + immed)); + PREF(instr, label); } else { // FIXME: tail? for (uint ofs = 0; ofs < access_size; ofs += 4) { - PRE(instr, - mov_st(drcontext, OPND_CREATE_MEM32(R1, ofs), OPND_CREATE_INT32(0))); + instr_t *label = INSTR_CREATE_label(drcontext); + opnd_t immed = OPND_CREATE_INT32(0); + PRE(instr, cmp(drcontext, OPND_CREATE_MEM32(R1, ofs), immed)); + PRE(instr, jcc(drcontext, OP_je, opnd_create_instr(label))); + PRE(instr, mov_st(drcontext, OPND_CREATE_MEM32(R1, ofs), immed)); + PREF(instr, label) } } |