bitpattern: add analysis effort limit, use in proc_rmdead

kernel/bitpattern.h

@@ -25,6 +25,12 @@
 
 YOSYS_NAMESPACE_BEGIN
 
+enum TakeResult {
+	FALSE,
+	TRUE,
+	TOO_BIG
+};
+
 /**
  * This file implements BitPatternPool for efficiently storing and querying
  * sets of fixed-width 2-valued logic constants compressed as "bit patterns".
@@ -39,6 +45,7 @@ YOSYS_NAMESPACE_BEGIN
  */
 struct BitPatternPool
 {
+	size_t limit = SIZE_MAX;
 	int width;
 	struct bits_t {
 		std::vector<RTLIL::State> bitdata;
@@ -167,9 +174,10 @@ struct BitPatternPool
 	 * Taking 011 out of pool({01a}) -> pool({010}), returns true.
 	 * Taking 011 out of pool({010}) does nothing, returns false.
 	 */
-	bool take(RTLIL::SigSpec sig)
+	[[nodiscard]]
+	TakeResult take(RTLIL::SigSpec sig)
 	{
-		bool status = false;
+		TakeResult status = FALSE;
 		bits_t bits = sig2bits(sig);
 		for (auto it = database.begin(); it != database.end();)
 			if (match(*it, bits)) {
@@ -180,12 +188,15 @@ struct BitPatternPool
 					new_pattern.bitdata = it->bitdata;
 					new_pattern[i] = bits[i] == RTLIL::State::S1 ? RTLIL::State::S0 : RTLIL::State::S1;
 					database.insert(new_pattern);
+					if (database.size() > limit)
+						return TOO_BIG;
 				}
 				it = database.erase(it);
-				status = true;
+				status = TRUE;
 				continue;
 			} else
 				++it;
+
 		return status;
 	}
 

passes/proc/proc_mux.cc

@@ -383,7 +383,7 @@ RTLIL::SigSpec signal_to_mux_tree(RTLIL::Module *mod, SnippetSwCache &swcache, d
 					if (!pat.is_fully_const())
 						extra_group_for_next_case = true;
 					else if (!ifxmode)
-						pool.take(pat);
+						log_assert(pool.take(pat) != TakeResult::TOO_BIG);
 			}
 		}
 

passes/proc/proc_rmdead.cc

@@ -54,12 +54,14 @@ struct FullyDefinedPool
 		: max_patterns{signal.size() >= 32 ? 0ul : 1ul << signal.size()}
 	{}
 
-	bool take(RTLIL::SigSpec sig)
+	// Yes, we never return TOO_BIG, since FullyDefinedPool::max_patterns
+	// and BitPatternPool::limits are different concepts
+	TakeResult take(RTLIL::SigSpec sig)
 	{
 		if (default_reached || patterns.count(sig))
-			return false;
+			return FALSE;
 		patterns.insert(sig);
-		return true;
+		return TRUE;
 	}
 
 	void take_all()
@@ -81,20 +83,24 @@ struct FullyDefinedPool
 void proc_rmdead(RTLIL::SwitchRule *sw, int &counter, int &full_case_counter);
 
 template <class Pool>
-static void proc_rmdead_impl(RTLIL::SwitchRule *sw, int &counter, int &full_case_counter)
+static void proc_rmdead_impl(Pool& pool, RTLIL::SwitchRule *sw, int &counter, int &full_case_counter)
 {
-	Pool pool(sw->signal);
-
+	bool is_too_big = false;
 	for (size_t i = 0; i < sw->cases.size(); i++)
 	{
 		bool is_default = GetSize(sw->cases[i]->compare) == 0 && (!pool.empty() || GetSize(sw->signal) == 0);
-
-		for (size_t j = 0; j < sw->cases[i]->compare.size(); j++) {
-			RTLIL::SigSpec sig = sw->cases[i]->compare[j];
-			if (!sig.is_fully_const())
-				continue;
-			if (!pool.take(sig))
-				sw->cases[i]->compare.erase(sw->cases[i]->compare.begin() + (j--));
+		if (!is_too_big) {
+			for (size_t j = 0; j < sw->cases[i]->compare.size(); j++) {
+				RTLIL::SigSpec sig = sw->cases[i]->compare[j];
+				if (!sig.is_fully_const())
+					continue;
+				auto res = pool.take(sig);
+				if (res == TakeResult::TOO_BIG) {
+					is_too_big = true; // Skip the rest of the analysis
+				}
+				if (res == TakeResult::FALSE)
+					sw->cases[i]->compare.erase(sw->cases[i]->compare.begin() + (j--));
+			}
 		}
 
 		if (!is_default) {
@@ -104,8 +110,6 @@ static void proc_rmdead_impl(RTLIL::SwitchRule *sw, int &counter, int &full_case
 				counter++;
 				continue;
 			}
-			// if (pool.empty())
-			// 	sw->cases[i]->compare.clear();
 		}
 
 		for (auto switch_it : sw->cases[i]->switches)
@@ -123,10 +127,14 @@ static void proc_rmdead_impl(RTLIL::SwitchRule *sw, int &counter, int &full_case
 
 void proc_rmdead(RTLIL::SwitchRule *sw, int &counter, int &full_case_counter)
 {
-	if (can_use_fully_defined_pool(sw))
-		proc_rmdead_impl<FullyDefinedPool>(sw, counter, full_case_counter);
-	else
-		proc_rmdead_impl<BitPatternPool>(sw, counter, full_case_counter);
+	if (can_use_fully_defined_pool(sw)) {
+		auto pool = FullyDefinedPool(sw->signal);
+		proc_rmdead_impl<FullyDefinedPool>(pool, sw, counter, full_case_counter);
+	}	else {
+		auto pool = BitPatternPool(sw->signal);
+		pool.limit = 100000;
+		proc_rmdead_impl<BitPatternPool>(pool, sw, counter, full_case_counter);
+	}
 }
 
 struct ProcRmdeadPass : public Pass {

tests/unit/kernel/bitpatternTest.cc

@@ -27,6 +27,12 @@ TEST(BitpatternTest, has)
     // 01a is not covered by 011
     EXPECT_FALSE(BitPatternPool(_011).has_all(_01a));
     EXPECT_FALSE(BitPatternPool(_111).has_all(_01a));
+    // test mutating and analysis effort limits
+    auto pool = BitPatternPool(3);
+    pool.limit = 4;
+    EXPECT_EQ(pool.take(_111), TakeResult::TRUE);
+    EXPECT_EQ(pool.take(_111), TakeResult::FALSE);
+    EXPECT_EQ(pool.take(_01a), TakeResult::TOO_BIG);
 }
 
 YOSYS_NAMESPACE_END