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[mono] Don't use recursion in mono_ssa_rename_vars (#61677)
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Implements #60266

Avoid deep recursion in `mono_ssa_rename_vars`, change the way we traverse
dominated bb's. Instead of using recursion, use stack-like array to
store information about stack history and the traversal.

The performance remains the same (or is slightly better) than before.
Times for the compilation of repro from #57141
(JIT time minimum from 5 runs):

Before:

    LLVM output file: './Uno.UI.FluentTheme.dll.bc.tmp'.
    JIT time: 4810 ms, Generation time: 2040 ms, Assembly+Link time: 2 ms.

After:

    LLVM output file: './Uno.UI.FluentTheme.dll.bc.tmp'.
    JIT time: 4781 ms, Generation time: 2017 ms, Assembly+Link time: 2 ms.

* Fix assignment

* Apply suggestions from code review

Co-authored-by: imhameed <[email protected]>

* Remove casts we don't need

Co-authored-by: imhameed <[email protected]>
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@radekdoulik @imhameed
radekdoulik and imhameed authored Nov 23, 2021
1 parent 0f40573 commit b35c0ad
Showing 1 changed file with 133 additions and 75 deletions.
208 changes: 133 additions & 75 deletions src/mono/mono/mini/ssa.c
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Original file line number Diff line number Diff line change
Expand Up @@ -159,24 +159,47 @@ typedef struct {
int idx;
} RenameInfo;

/**
* mono_ssa_rename_vars:
* Implement renaming of SSA variables. Also compute def-use information in parallel.
* \p stack_history points to an area of memory which can be used for storing changes
* made to the stack, so they can be reverted later.
*/
static void
mono_ssa_rename_vars (MonoCompile *cfg, int max_vars, MonoBasicBlock *bb, gboolean *originals_used, MonoInst **stack, guint32 *lvreg_stack, gboolean *lvreg_defined, RenameInfo *stack_history, int stack_history_size)
rename_phi_arguments_in_out_bbs(MonoCompile *cfg, MonoBasicBlock *bb, MonoInst **stack)
{
MonoInst *ins, *new_var;
int i, j, idx;
GSList *tmp;
int stack_history_len = 0;
int i, j;

if (cfg->verbose_level >= 4)
printf ("\nRENAME VARS BLOCK %d:\n", bb->block_num);
for (i = 0; i < bb->out_count; i++) {
MonoBasicBlock *n = bb->out_bb [i];

for (j = 0; j < n->in_count; j++)
if (n->in_bb [j] == bb)
break;

for (ins = n->code; ins; ins = ins->next) {
if (MONO_IS_PHI (ins)) {
int idx = ins->inst_c0;
if (stack [idx])
new_var = stack [idx];
else
new_var = cfg->varinfo [idx];
#ifdef DEBUG_SSA
printf ("FOUND PHI %d (%d, %d)\n", idx, j, new_var->inst_c0);
#endif
ins->inst_phi_args [j + 1] = new_var->dreg;
record_use (cfg, new_var, n, ins);
if (G_UNLIKELY (cfg->verbose_level >= 4))
printf ("\tAdd PHI R%d <- R%d to BB%d\n", ins->dreg, new_var->dreg, n->block_num);
}
else
/* The phi nodes are at the beginning of the bblock */
break;
}
}
}

static int
create_new_vars (MonoCompile *cfg, int max_vars, MonoBasicBlock *bb, gboolean *originals_used, MonoInst **stack, guint32 *lvreg_stack, gboolean *lvreg_defined, RenameInfo **stack_history, int *stack_history_size)
{
MonoInst *ins, *new_var;
int i, stack_history_len = 0;

/* First pass: Create new vars */
for (ins = bb->code; ins; ins = ins->next) {
const char *spec = INS_INFO (ins->opcode);
int num_sregs;
Expand Down Expand Up @@ -233,21 +256,21 @@ mono_ssa_rename_vars (MonoCompile *cfg, int max_vars, MonoBasicBlock *bb, gboole
MonoMethodVar *info;

if (var && !(var->flags & (MONO_INST_VOLATILE|MONO_INST_INDIRECT))) {
idx = var->inst_c0;
int idx = var->inst_c0;
g_assert (idx < max_vars);

if (var->opcode == OP_ARG)
originals_used [idx] = TRUE;

if (stack_history_len + 128 > stack_history_size) {
stack_history_size += 1024;
RenameInfo *new_history = mono_mempool_alloc (cfg->mempool, sizeof (RenameInfo) * stack_history_size);
memcpy (new_history, stack_history, stack_history_len * sizeof (RenameInfo));
stack_history = new_history;
if (stack_history_len + 128 > *stack_history_size) {
*stack_history_size += 1024;
RenameInfo *new_history = mono_mempool_alloc (cfg->mempool, sizeof (RenameInfo) * *stack_history_size);
memcpy (new_history, *stack_history, stack_history_len * sizeof (RenameInfo));
*stack_history = new_history;
}

stack_history [stack_history_len].var = stack [idx];
stack_history [stack_history_len].idx = idx;
(*stack_history) [stack_history_len].var = stack [idx];
(*stack_history) [stack_history_len].idx = idx;
stack_history_len ++;

if (originals_used [idx]) {
Expand Down Expand Up @@ -284,49 +307,102 @@ mono_ssa_rename_vars (MonoCompile *cfg, int max_vars, MonoBasicBlock *bb, gboole
#ifdef DEBUG_SSA
printf ("\tAfter processing "); mono_print_ins (ins);
#endif
}

return stack_history_len;
}

static void
restore_stack (MonoInst **stack, RenameInfo *stack_history, int stack_history_len)
{
int i = stack_history_len;
while (i-- > 0) {
stack [stack_history [i].idx] = stack_history [i].var;
}
}

/* Rename PHI arguments in succeeding bblocks */
for (i = 0; i < bb->out_count; i++) {
MonoBasicBlock *n = bb->out_bb [i];
typedef struct {
GSList *blocks;
RenameInfo *history;
int size;
int len;
} RenameStackInfo;

for (j = 0; j < n->in_count; j++)
if (n->in_bb [j] == bb)
break;

for (ins = n->code; ins; ins = ins->next) {
if (MONO_IS_PHI (ins)) {
idx = ins->inst_c0;
if (stack [idx])
new_var = stack [idx];
else
new_var = cfg->varinfo [idx];
#ifdef DEBUG_SSA
printf ("FOUND PHI %d (%d, %d)\n", idx, j, new_var->inst_c0);
#endif
ins->inst_phi_args [j + 1] = new_var->dreg;
record_use (cfg, new_var, n, ins);
if (G_UNLIKELY (cfg->verbose_level >= 4))
printf ("\tAdd PHI R%d <- R%d to BB%d\n", ins->dreg, new_var->dreg, n->block_num);
/**
* mono_ssa_rename_vars:
* Implement renaming of SSA variables. Also compute def-use information in parallel.
* \p stack_history points to an area of memory which can be used for storing changes
* made to the stack, so they can be reverted later.
*/
static void
mono_ssa_rename_vars (MonoCompile *cfg, int max_vars, MonoBasicBlock *bb)
{
GSList *blocks = NULL;
RenameStackInfo* rename_stack;
int rename_stack_size, rename_stack_idx = 0;
RenameInfo *stack_history;
int stack_history_size;
gboolean *originals;
guint32 *lvreg_stack;
gboolean *lvreg_defined;
MonoInst **stack;

stack = g_newa (MonoInst*, cfg->num_varinfo);
memset (stack, 0, sizeof (MonoInst *) * cfg->num_varinfo);
lvreg_stack = g_new0 (guint32, cfg->next_vreg);
lvreg_defined = g_new0 (gboolean, cfg->next_vreg);
stack_history_size = 10240;
stack_history = g_new (RenameInfo, stack_history_size);
originals = g_new0 (gboolean, cfg->num_varinfo);
rename_stack_size = 16;
rename_stack = g_new (RenameStackInfo, rename_stack_size);

do {
if (G_UNLIKELY (cfg->verbose_level >= 4))
printf ("\nRENAME VARS BLOCK %d:\n", bb->block_num);

int stack_history_len = create_new_vars (cfg, max_vars, bb, originals, stack, lvreg_stack, lvreg_defined, &stack_history, &stack_history_size);
rename_phi_arguments_in_out_bbs (cfg, bb, stack);

if (bb->dominated) {
if (rename_stack_idx >= rename_stack_size - 1) {
rename_stack_size += MIN(rename_stack_size, 1024);
rename_stack = g_realloc(rename_stack, sizeof(RenameStackInfo)*rename_stack_size);
}
else
/* The phi nodes are at the beginning of the bblock */
break;
}
}

if (bb->dominated) {
for (tmp = bb->dominated; tmp; tmp = tmp->next) {
mono_ssa_rename_vars (cfg, max_vars, (MonoBasicBlock *)tmp->data, originals_used, stack, lvreg_stack, lvreg_defined, stack_history + stack_history_len, stack_history_size - stack_history_len);
RenameStackInfo* info = rename_stack + rename_stack_idx;
rename_stack_idx++;
info->blocks = blocks;
info->history = stack_history;
info->size = stack_history_size;
info->len = stack_history_len;
stack_history += stack_history_len;
stack_history_size -= stack_history_len;
blocks = bb->dominated;
} else {
restore_stack (stack, stack_history, stack_history_len);
blocks = blocks->next;

while (!blocks && rename_stack_idx > 0) {
rename_stack_idx--;
RenameStackInfo* info = rename_stack + rename_stack_idx;
blocks = info->blocks ? info->blocks->next : NULL;
stack_history = info->history;
stack_history_size = info->size;
stack_history_len = info->len;
restore_stack (stack, stack_history, stack_history_len);
}
}
}

/* Restore stack */
for (i = stack_history_len - 1; i >= 0; i--) {
stack [stack_history [i].idx] = stack_history [i].var;
}
if (blocks)
bb = (MonoBasicBlock*) blocks->data;
} while (blocks);

g_free (stack_history);
g_free (originals);
g_free (lvreg_stack);
g_free (lvreg_defined);
g_free (rename_stack);
cfg->comp_done |= MONO_COMP_SSA_DEF_USE;
}

Expand All @@ -336,13 +412,8 @@ mono_ssa_compute (MonoCompile *cfg)
int i, j, idx, bitsize;
MonoBitSet *set;
MonoMethodVar *vinfo = g_new0 (MonoMethodVar, cfg->num_varinfo);
MonoInst *ins, **stack;
MonoInst *ins;
guint8 *buf, *buf_start;
RenameInfo *stack_history;
int stack_history_size;
gboolean *originals;
guint32 *lvreg_stack;
gboolean *lvreg_defined;

g_assert (!(cfg->comp_done & MONO_COMP_SSA));

Expand Down Expand Up @@ -464,20 +535,7 @@ mono_ssa_compute (MonoCompile *cfg)
g_free (buf_start);

/* Renaming phase */

stack = g_newa (MonoInst*, cfg->num_varinfo);
memset (stack, 0, sizeof (MonoInst *) * cfg->num_varinfo);

lvreg_stack = g_new0 (guint32, cfg->next_vreg);
lvreg_defined = g_new0 (gboolean, cfg->next_vreg);
stack_history_size = 10240;
stack_history = g_new (RenameInfo, stack_history_size);
originals = g_new0 (gboolean, cfg->num_varinfo);
mono_ssa_rename_vars (cfg, cfg->num_varinfo, cfg->bb_entry, originals, stack, lvreg_stack, lvreg_defined, stack_history, stack_history_size);
g_free (stack_history);
g_free (originals);
g_free (lvreg_stack);
g_free (lvreg_defined);
mono_ssa_rename_vars (cfg, cfg->num_varinfo, cfg->bb_entry);

if (cfg->verbose_level >= 4)
printf ("\nEND COMPUTE SSA.\n\n");
Expand Down

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