NAME 
compilers/imcc/optimizer.c
DESCRIPTION
Optimization occurs in three stages: 1) pre_optimizer -- runs before control flow graph (CFG) is built 2) optimizer -- runs after CFG is built, but before register allocation 3) post_optimizer -- runs after register allocation
pre_optimizer -------------
During pre-optimization we perform optimizations which don't require full knowledge of the control flow graph and the life ranges of each variable. This phase is handled by two functions: pre_optimize() and cfg_optimize().
pre_optimize() runs before the construction of the CFG begins. It calls strength_reduce() to perform simple strength reduction, and if_branch() to rewrite certain if/branch/label constructs (for details, see if_branch() below).
[pre_optimize() may also be called later, during the main optimization phase, but this is not guaranteed.]
cfg_optimize() runs during the construction of the CFG. It calls branch_branch() to perform jump optimization (i.e. branches to branch statements or jumps to jumps are converted into single branches/jumps to the final destination), unused_label() to remove unused labels and dead_code_remove() to remove unreachable code (e.g. basic blocks which are never entered or instructions after and unconditional branch which are never branched to).
cfg_optimize may be called multiple times during the construction of the CFG depending on whether or not it finds anything to optimize.
RT#46277: subst_constants ... rewrite e.g. add_i_ic_ic -- where does this happen?
optimizer ---------
runs with CFG and life info
used_once ... deletes assignments, when LHS is unused loop_optimization ... pulls invariants out of loops RT#46279 e.g. constant_propagation
post_optimizer: currently pcc_optimize in pcc.c ---------------
runs after register alloocation
e.g. eliminate new Px .PerlUndef because Px where different before
Functions
int pre_optimize- Handles optimizations occuring before the construction of the CFG.
int cfg_optimize- Handles optimizations occuring during the construction of the CFG. Returns TRUE if any optimization was performed. Otherwise, returns FALSE.
int optimize- RT#48260: Not yet documented!!!
const char *get_neg_op- Get negated form of operator. If no negated form is known, return NULL.
static int if_branch- Convert if/branch/label constructs of the form:
- to the simpler negated form:
static int strength_reduce- strength_reduce ... rewrites e.g add Ix, Ix, y => add Ix, y
- These are run after constant simplification, so it is guaranteed that one operand is non constant if opsize == 4
static int constant_propagation- Does conservative constant propagation. This code will not propagate constants past labels or saves, even though sometimes it may be safe.
Instruction *IMCC_subst_constants_umix- rewrite e.g. add_n_ic => add_n_nc
static int eval_ins- Run one parrot instruction, registers are filled with the according constants. Thus the result is always ok as the function core evaluates the constants.
Instruction *IMCC_subst_constants- rewrite e.g. add_n_nc_nc => set_n_nc abs_i_ic => set_i_ic eq_ic_ic_ic => branch_ic / delete if_ic_ic => branch_ic / delete
static int branch_branch- if I0 goto L1 => if IO goto L2 ... L1: branch L2
- Returns TRUE if any optimizations were performed. Otherwise, returns FALSE.
static int branch_reorg- branch L2 => ... L1: branch L4 ... L1: branch L3 ... L2: branch L3 ... L5: branch L4 L5:
- Returns TRUE if any optimizations were performed. Otherwise, returns FALSE.
static int branch_cond_loop_swap- RT#48260: Not yet documented!!!
static int branch_cond_loop- start: => start: if cond goto end if cond goto end ... branch start start_post1: end: ... unless cond goto start_post562 end:
- The basic premise is "branch (A) to conditional (B), where B goes to just after A."
- Returns TRUE if any optimizations were performed. Otherwise, returns FALSE.
static int unused_label- Removes unused labels. A label is unused if ... [RT#46287: finish this].
- Returns TRUE if any optimizations were performed. Otherwise, returns FALSE.
static int dead_code_remove- RT#48260: Not yet documented!!!
static int used_once- RT#48260: Not yet documented!!!
static int _is_ins_save- RT#48260: Not yet documented!!!
static int is_ins_save- RT#48260: Not yet documented!!!
int max_loop_depth- RT#48260: Not yet documented!!!
int is_invariant- RT#48260: Not yet documented!!!
Basic_block *find_outer- RT #48260: Not yet documented!!!
int move_ins_out- move the instruction ins before loop in bb
int loop_one- RT#48260: Not yet documented!!!
int loop_optimization- RT#48260: Not yet documented!!!
if cond L1
branch L2
L1
unless cond L2
