From 4cdcfe8b143367fb207824c97c0f84eab21c40c3 Mon Sep 17 00:00:00 2001
From: Andrea Shepard <andrea@persephoneslair.org>
Date: Sun, 20 Nov 2016 03:26:49 +0000
Subject: [PATCH] Implement CHARSET_ACTION_SPLIT and CHARSET_ACTION_BITMAP
---
src/backends/llvm.c | 280 ++++++++++++++++++++++++++++++++++++++++----
1 file changed, 258 insertions(+), 22 deletions(-)
diff --git a/src/backends/llvm.c b/src/backends/llvm.c
index 4174b385..299c74f5 100644
--- a/src/backends/llvm.c
+++ b/src/backends/llvm.c
@@ -157,6 +157,11 @@ typedef enum {
* character.
*/
CHARSET_ACTION_SCAN,
+ /*
+ * Bitmap action; test input char against a bitmap in the IR at fixed
+ * cost.
+ */
+ CHARSET_ACTION_BITMAP,
/*
* Complement action; invert the sense of the charset. This action type
* has one child node, with the bounds unchanged and the portion of the
@@ -191,6 +196,12 @@ struct llvm_charset_exec_plan_s {
};
/* Forward prototypes for charset llvm stuff */
+static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
+ llvm_charset_exec_plan_t *parent, llvm_charset_exec_plan_t *cep,
+ int allow_complement, uint8_t *split_point);
+static llvm_charset_exec_plan_t * h_llvm_build_charset_exec_plan_impl_alloc(
+ HAllocator* mm__, llvm_charset_exec_plan_t *parent, HCharset cs,
+ uint8_t idx_start, uint8_t idx_end, int allow_complement);
static void h_llvm_free_charset_exec_plan(HAllocator* mm__,
llvm_charset_exec_plan_t *cep);
@@ -226,6 +237,164 @@ static int h_llvm_charset_estimate_scan_cost(HCharset cs, uint8_t idx_start, uin
return cost;
}
+/*
+ * Given a skeletal CHARSET_ACTION_SPLIT node from h_llvm_build_charset_exec_plan_impl(),
+ * binary search for the best split point we can find and return the cost metric.
+ * Unfortunately the search space is quite large, so we're going to use some silly
+ * heuristics here such as looking for the longest run of present or absent chars at
+ * one end of a charset, and proposing it as a split, or just trying the midpoint.
+ * It may be possible to do better.
+ */
+
+static int h_llvm_find_best_split(HAllocator* mm__, llvm_charset_exec_plan_t *split) {
+ int rv, best_end_run, isset, i, contiguous;
+ uint8_t best_end_run_split, midpoint;
+ llvm_charset_exec_plan_t *best_left, *best_right, *left, *right;
+ int best_cost, cost;
+
+ /* Sanity-check: we should be a split with a range at least two indices long */
+ if (!split || split->action != CHARSET_ACTION_SPLIT) return -1;
+ if (split->idx_end <= split->idx_start) return -1;
+
+ /* Find the longest end run; split a run of length 1 at the left end as a
+ * fallback, since there's always a run of length 1 at each end. */
+ best_end_run = 1;
+ best_end_run_split = split->idx_start;
+ contiguous = 0;
+ /* Try the low end */
+ i = 0;
+ while (i <= split->idx_end - split->idx_start &&
+ (charset_isset(split->cs, split->idx_start + i) ==
+ charset_isset(split->cs, split->idx_start))) ++i;
+ if (i <= split->idx_end - split->idx_start) {
+ /* This run has length i */
+ if (i > best_end_run) {
+ best_end_run = i;
+ /*
+ * -1 since split points are last index of left child, and i
+ * is first index that wasn't in the run
+ */
+ best_end_run_split = split->idx_start + i - 1;
+ }
+
+ /* Now the same thing from the high end */
+ i = 0;
+ while (i <= split->idx_end - split->idx_start &&
+ (charset_isset(split->cs, split->idx_end - i) ==
+ charset_isset(split->cs, split->idx_end))) ++i;
+ if (i <= split->idx_end - split->idx_start && i > best_end_run) {
+ best_end_run = i;
+ best_end_run_split = split->idx_end - i;
+ }
+ } else {
+ /* Wow, contiguous - any split will turn out well - just use the midpoint */
+ contiguous = 1;
+ }
+
+ /* Initialize, start trying things */
+ best_left = best_right = left = right = NULL;
+ rv = -1;
+
+ /* Try a midpoint split */
+ midpoint = split->idx_start + (split->idx_end - split->idx_start) / 2;
+ left = h_llvm_build_charset_exec_plan_impl_alloc(mm__, split, split->cs,
+ split->idx_start, midpoint, 1);
+ right = h_llvm_build_charset_exec_plan_impl_alloc(mm__, split, split->cs,
+ midpoint + 1, split->idx_end, 1);
+ if (left && right) {
+ /* Cost of the split == 1 + max(left->cost, right->cost) */
+ cost = left->cost;
+ if (right->cost > cost) cost = right->cost;
+ ++cost;
+ /* We haven't tried the end-run one yet, so always accept this */
+ best_left = left;
+ best_right = right;
+ best_cost = cost;
+ left = right = NULL;
+ } else goto err;
+
+ /*
+ * Try an end-run split; if we decided we had a contiguous run earlier,
+ * all are equally good, so don't bother and just use the midpoint
+ */
+
+ if (!contiguous) {
+ /*
+ * Sanity-check the indices; error out if the scanner gave us
+ * something silly
+ */
+ if (best_end_run_split < split->idx_start ||
+ best_end_run_split >= split->idx_end) goto err;
+ left = h_llvm_build_charset_exec_plan_impl_alloc(mm__, split, split->cs,
+ split->idx_start, best_end_run_split, 1);
+ right = h_llvm_build_charset_exec_plan_impl_alloc(mm__, split, split->cs,
+ best_end_run_split + 1, split->idx_end, 1);
+ if (left && right) {
+ /* Cost of the split == 1 + max(left->cost, right->cost) */
+ cost = left->cost;
+ if (right->cost > cost) cost = right->cost;
+ ++cost;
+ /* Check if against what we already have */
+ if (cost < best_cost) {
+ if (best_left) h_llvm_free_charset_exec_plan(mm__, best_left);
+ if (best_right) h_llvm_free_charset_exec_plan(mm__, best_right);
+ best_left = left;
+ best_right = right;
+ best_cost = cost;
+ left = right = NULL;
+ }
+ } else goto err;
+ }
+
+ /* Set up the split node with our best results */
+ split->cost = best_cost;
+ split->children[0] = best_left;
+ split->children[1] = best_right;
+ split->split_point = best_left->idx_end;
+ best_left = best_right = NULL;
+ rv = split->cost;
+
+ err:
+ /* Error/cleanup case */
+ if (left) h_llvm_free_charset_exec_plan(mm__, left);
+ if (right) h_llvm_free_charset_exec_plan(mm__, right);
+ if (best_left) h_llvm_free_charset_exec_plan(mm__, best_left);
+ if (best_right) h_llvm_free_charset_exec_plan(mm__, best_right);
+
+ return rv;
+}
+
+/*
+ * Setup call to h_llvm_build_charset_exec_plan_impl(), while allocating a new
+ * llvm_charset_exec_plan_t.
+ */
+static llvm_charset_exec_plan_t * h_llvm_build_charset_exec_plan_impl_alloc(
+ HAllocator* mm__, llvm_charset_exec_plan_t *parent, HCharset cs,
+ uint8_t idx_start, uint8_t idx_end, int allow_complement) {
+ int cost;
+ llvm_charset_exec_plan_t *cep;
+
+ if (!mm__) return NULL;
+ if (!cs) return NULL;
+ if (idx_start > idx_end) return NULL;
+
+ cep = h_new(llvm_charset_exec_plan_t, 1);
+ memset(cep, 0, sizeof(*cep));
+ cep->cs = copy_charset(mm__, cs);
+ cep->idx_start = idx_start;
+ cep->idx_end = idx_end;
+ charset_restrict_to_range(cep->cs, idx_start, idx_end);
+ cost = h_llvm_build_charset_exec_plan_impl(mm__, cep->cs, parent, cep,
+ allow_complement, NULL);
+ if (cost >= 0) cep->cost = cost;
+ else {
+ h_llvm_free_charset_exec_plan(mm__, cep);
+ cep = NULL;
+ }
+
+ return cep;
+}
+
/*
* Given a charset, optionally its parent containing range restrictions, and
* an allow_complement parameter, search for the best exec plan and write it
@@ -239,9 +408,10 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
int allow_complement, uint8_t *split_point) {
int eligible_for_accept, best_cost;
int estimated_complement_cost, estimated_scan_cost, estimated_split_cost;
+ int estimated_bitmap_cost;
uint8_t idx_start, idx_end;
HCharset complement;
- llvm_charset_exec_plan_t complement_cep;
+ llvm_charset_exec_plan_t complement_cep, split_cep;
llvm_charset_exec_plan_action_t chosen_action;
/* Check args */
@@ -249,9 +419,17 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
/*
* The index bounds come from either the parent or maximal bounds by
- * default.
+ * default. Exception is the case that we are a child of a split, in
+ * which case h_llvm_find_best_split() should have set bounds in cep.
*/
- if (parent) {
+ if (parent && parent->action == CHARSET_ACTION_SPLIT &&
+ ((cep->idx_start == parent->idx_start &&
+ cep->idx_end < parent->idx_end) ||
+ (cep->idx_start > parent->idx_start &&
+ cep->idx_end == parent->idx_end))) {
+ idx_start = cep->idx_start;
+ idx_end = cep->idx_end;
+ } else if (parent) {
idx_start = parent->idx_start;
idx_end = parent->idx_end;
} else {
@@ -267,7 +445,8 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
cep->idx_start = idx_start;
cep->idx_end = idx_end;
cep->split_point = 0;
- cep->cost = 1;
+ /* Acceptance (or rejection, under a complement) is free */
+ cep->cost = 0;
cep->action = CHARSET_ACTION_ACCEPT;
cep->children[0] = NULL;
cep->children[1] = NULL;
@@ -279,6 +458,11 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
* CHARSET_ACTION_COMPLEMENT if we are eligible to use it.
*/
estimated_scan_cost = h_llvm_charset_estimate_scan_cost(cs, idx_start, idx_end);
+ /*
+ * We can always use CHARSET_ACTION_BITMAP; this constant controls how
+ * strongly we prefer it over the compare-and-branch approach.
+ */
+ estimated_bitmap_cost = 6;
/* >= 0 is a flag we have a complement we may need to free later */
estimated_complement_cost = -1;
if (allow_complement) {
@@ -299,20 +483,28 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
memset(complement_cep.children[0], 0, sizeof(llvm_charset_exec_plan_t));
complement_cep.children[1] = NULL;
/*
- * Find the child; the complement itself has cost 1; we set
- * allow_complement = 0 so we never stack two complements
+ * Find the child; the complement has cost 0 since it just swizzles success
+ * and fail output basic blocks; it's important we test for complement last
+ * below then, so we break ties in favor of not stacking complements up. We
+ * set allow_complement = 0 so we never stack two complements.
*/
- complement_cep.cost = 1 +
- h_llvm_build_charset_exec_plan_impl(mm__, child_cs, &complement_cep,
- complement_cep.children[0], 0, NULL);
+ complement_cep.cost = h_llvm_build_charset_exec_plan_impl(mm__, child_cs, &complement_cep,
+ complement_cep.children[0], 0, NULL);
estimated_complement_cost = complement_cep.cost;
h_free(child_cs);
}
- /* Should we just terminate search below a certain scan cost perhaps? */
-
- estimated_split_cost = -1;
- /* TODO splits */
+ /* Set up split node */
+ split_cep.cs = copy_charset(mm__, cs);
+ charset_restrict_to_range(split_cep.cs, idx_start, idx_end);
+ split_cep.idx_start = idx_start;
+ split_cep.idx_end = idx_end;
+ split_cep.split_point = 0;
+ split_cep.action = CHARSET_ACTION_SPLIT;
+ split_cep.cost = -1;
+ split_cep.children[0] = NULL;
+ split_cep.children[1] = NULL;
+ estimated_split_cost = h_llvm_find_best_split(mm__, &split_cep);
/* Pick the action type with the lowest cost */
best_cost = -1;
@@ -322,10 +514,10 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
best_cost = estimated_scan_cost;
}
- if (allow_complement && estimated_complement_cost >= 0 &&
- (best_cost < 0 || estimated_complement_cost < best_cost)) {
- chosen_action = CHARSET_ACTION_COMPLEMENT;
- best_cost = estimated_complement_cost;
+ if (estimated_bitmap_cost >= 0 &&
+ (best_cost < 0 || estimated_bitmap_cost < best_cost)) {
+ chosen_action = CHARSET_ACTION_BITMAP;
+ best_cost = estimated_bitmap_cost;
}
if (estimated_split_cost >= 0 &&
@@ -334,6 +526,12 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
best_cost = estimated_split_cost;
}
+ if (allow_complement && estimated_complement_cost >= 0 &&
+ (best_cost < 0 || estimated_complement_cost < best_cost)) {
+ chosen_action = CHARSET_ACTION_COMPLEMENT;
+ best_cost = estimated_complement_cost;
+ }
+
/* Fill out cep based on the chosen action */
switch (chosen_action) {
case CHARSET_ACTION_SCAN:
@@ -348,6 +546,18 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
cep->children[0] = NULL;
cep->children[1] = NULL;
break;
+ case CHARSET_ACTION_BITMAP:
+ /* Set up a bitmap */
+ cep->cs = copy_charset(mm__, cs);
+ charset_restrict_to_range(cep->cs, idx_start, idx_end);
+ cep->idx_start = idx_start;
+ cep->idx_end = idx_end;
+ cep->split_point = 0;
+ cep->action = CHARSET_ACTION_BITMAP;
+ cep->cost = estimated_bitmap_cost;
+ cep->children[0] = NULL;
+ cep->children[1] = NULL;
+ break;
case CHARSET_ACTION_COMPLEMENT:
/*
* We have a CEP filled out we can just copy over; be sure to set
@@ -359,10 +569,14 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
estimated_complement_cost = -1;
break;
case CHARSET_ACTION_SPLIT:
- /* Not yet supported (TODO) */
- best_cost = -1;
- memset(cep, 0, sizeof(*cep));
- if (split_point) *split_point = 0;
+ /*
+ * We have a CEP filled out we can just copy over; be sure to set
+ * estimated_split_cost = -1 so we know not to free it on the way
+ * out.
+ */
+ memcpy(cep, &split_cep, sizeof(split_cep));
+ memset(&split_cep, 0, sizeof(split_cep));
+ estimated_split_cost = -1;
break;
default:
/* Not supported */
@@ -372,13 +586,31 @@ static int h_llvm_build_charset_exec_plan_impl(HAllocator* mm__, HCharset cs,
}
}
+ /* Free temporary CEPs if needed */
+
if (estimated_complement_cost >= 0) {
- /* We have a complement_cep we ended up not using; free its child */
+ /*
+ * We have a complement_cep we ended up not using; free its child and
+ * charset
+ */
h_llvm_free_charset_exec_plan(mm__, complement_cep.children[0]);
+ h_free(complement_cep.cs);
memset(&complement_cep, 0, sizeof(complement_cep));
estimated_complement_cost = -1;
}
+ if (estimated_split_cost >= 0) {
+ /*
+ * We have a split_cep we ended up not using; free its children and
+ * charset.
+ */
+ h_llvm_free_charset_exec_plan(mm__, split_cep.children[0]);
+ h_llvm_free_charset_exec_plan(mm__, split_cep.children[1]);
+ h_free(split_cep.cs);
+ memset(&split_cep, 0, sizeof(split_cep));
+ estimated_split_cost = -1;
+ }
+
return best_cost;
}
@@ -444,6 +676,7 @@ static bool h_llvm_check_charset_exec_plan(llvm_charset_exec_plan_t *cep) {
switch (cep->action) {
case CHARSET_ACTION_ACCEPT:
case CHARSET_ACTION_SCAN:
+ case CHARSET_ACTION_BITMAP:
/* These are always okay and have no children */
if (cep->children[0] || cep->children[1]) goto done;
consistent = true;
@@ -545,6 +778,9 @@ static void h_llvm_pretty_print_charset_exec_plan_impl(HAllocator *mm__, llvm_ch
case CHARSET_ACTION_SCAN:
action_string = "CHARSET_ACTION_SCAN";
break;
+ case CHARSET_ACTION_BITMAP:
+ action_string = "CHARSET_ACTION_BITMAP";
+ break;
case CHARSET_ACTION_COMPLEMENT:
action_string = "CHARSET_ACTION_COMPLEMENT";
n_children = 1;
--
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