From: Ulya Trofimovich <skvadrik@gmail.com>
Date: Tue, 4 Apr 2017 12:41:41 +0000 (+0100)
Subject: Fixed liveness analysis inside of basic block.
X-Git-Tag: 1.0~39^2~86
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=55853fdc015c2c65a397165c7ef791662f6a063c;p=re2c

Fixed liveness analysis inside of basic block.

Liveness flows backwards through basic block, so it should be
propagated backwards starting with live-out set and applying
commands one by one in reverse order.
---

diff --git a/re2c/src/dfa/cfg/cfg.h b/re2c/src/dfa/cfg/cfg.h
index 1b9613ef..7c314b99 100644
--- a/re2c/src/dfa/cfg/cfg.h
+++ b/re2c/src/dfa/cfg/cfg.h
@@ -31,6 +31,7 @@ struct cfg_t
 	~cfg_t();
 	static tagver_t compact(const cfg_t &cfg, tagver_t *ver2new);
 	static void liveness_analysis(const cfg_t &cfg, bool *live);
+	static void live_through_bblock(const tcmd_t *cmd, bool *live);
 	static void dead_code_elimination(cfg_t &cfg, const bool *live);
 	static void interference(const cfg_t &cfg, const bool *live, bool *interf);
 	static tagver_t variable_allocation(const cfg_t &cfg, const bool *interf, tagver_t *ver2new);
diff --git a/re2c/src/dfa/cfg/dce.cc b/re2c/src/dfa/cfg/dce.cc
index 73f4639e..d4bc2cb8 100644
--- a/re2c/src/dfa/cfg/dce.cc
+++ b/re2c/src/dfa/cfg/dce.cc
@@ -9,6 +9,8 @@ void cfg_t::dead_code_elimination(cfg_t &cfg, const bool *live)
 	// final and fallback tags can't be dead by construction
 	cfg_bb_t *b = cfg.bblocks, *e = b + cfg.nbbarc;
 
+	// ignore possible local liveness inside of bblock:
+	// by construction we have no versions local to bblock
 	for (; b < e; ++b, live += nver) {
 		for (tcmd_t *p, **pp = &b->cmd; (p = *pp);) {
 			if (!live[p->lhs]) {
diff --git a/re2c/src/dfa/cfg/interfere.cc b/re2c/src/dfa/cfg/interfere.cc
index fc4efbc1..a83961f1 100644
--- a/re2c/src/dfa/cfg/interfere.cc
+++ b/re2c/src/dfa/cfg/interfere.cc
@@ -28,25 +28,21 @@ void interfere(const tcmd_t *cmd, const bool *live, bool *interf,
 {
 	// LHS of each command iterferes with all tags that are alive after
 	// this command except its RHS and tags that are are assigned to
-	// the same RHS by subsequent commands.
+	// the same RHS by other commands in this block.
 	memcpy(buf1, live, nver * sizeof(bool));
 	for (const tcmd_t *p = cmd; p; p = p->next) {
 		const tagver_t r = p->rhs;
 
-		// alive after this command: RHSs of subsequent commands
-		// and all tags alive after this basic block
+		// alive after this command
 		memcpy(buf2, buf1, nver * sizeof(bool));
-		for (const tcmd_t *q = p->next; q; q = q->next) {
-			const tagver_t v = q->rhs;
-			if (v != r && tcmd_t::iscopy(v)) {
-				buf2[v] = true;
-			}
-		}
+		cfg_t::live_through_bblock(p->next, buf2);
 
-		// exclude: tags equal to RHS of this command
+		// exclude RHS
 		if (tcmd_t::iscopy(r)) {
 			buf2[r] = false;
 		}
+
+		// exclude tags assigned to the same RHS
 		for (const tcmd_t *q = cmd; q; q = q->next) {
 			if (q->rhs == r) {
 				buf2[q->lhs] = false;
diff --git a/re2c/src/dfa/cfg/liveanal.cc b/re2c/src/dfa/cfg/liveanal.cc
index c88f0ccc..efe65d9e 100644
--- a/re2c/src/dfa/cfg/liveanal.cc
+++ b/re2c/src/dfa/cfg/liveanal.cc
@@ -23,6 +23,19 @@ static cfg_ix_t *postorder(const cfg_t &cfg, bool *done,
 	return ++ord;
 }
 
+void cfg_t::live_through_bblock(const tcmd_t *cmd, bool *live)
+{
+	if (!cmd) return;
+
+	live_through_bblock(cmd->next, live);
+
+	const tagver_t l = cmd->lhs, r = cmd->rhs;
+	if (live[l] && tcmd_t::iscopy(r)) {
+		live[r] = true;
+	}
+	live[l] = false;
+}
+
 void cfg_t::liveness_analysis(const cfg_t &cfg, bool *live)
 {
 	const std::vector<Tag> &tags = cfg.dfa.tags;
@@ -84,15 +97,7 @@ void cfg_t::liveness_analysis(const cfg_t &cfg, bool *live)
 				const tcmd_t *cmd = cfg.bblocks[*j].cmd;
 				memcpy(buf2, l, nver * sizeof(bool));
 
-				// need two passes: same version may occur as both LHS and RHS
-				for (const tcmd_t *p = cmd; p; p = p->next) {
-					buf2[p->lhs] = false;
-				}
-				for (const tcmd_t *p = cmd; p; p = p->next) {
-					if (l[p->lhs] && tcmd_t::iscopy(p->rhs)) {
-						buf2[p->rhs] = true;
-					}
-				}
+				cfg_t::live_through_bblock(cmd, buf2);
 
 				for (size_t v = 0; v < nver; ++v) {
 					buf1[v] |= buf2[v];
@@ -131,12 +136,14 @@ void cfg_t::liveness_analysis(const cfg_t &cfg, bool *live)
 		}
 
 		// need two passes: same version may occur as both LHS and RHS
+		// not the same as backward propagation of liveness through bblock
 		for (const tcmd_t *p = b->cmd; p; p = p->next) {
 			buf1[p->lhs] = false;
 		}
 		for (const tcmd_t *p = b->cmd; p; p = p->next) {
-			if (tcmd_t::iscopy(p->rhs)) {
-				buf1[p->rhs] = true;
+			const tagver_t v = p->rhs;
+			if (tcmd_t::iscopy(v)) {
+				buf1[v] = true;
 			}
 		}