cxxrtl: use CXXRTL_ASSERT for RTL contract violations instead of assert.

RTL contract violations and C++ contract violations are different:
the former depend on the netlist and will never violate memory safety
whereas the latter may. When loading a CXXRTL simulation into another
process, RTL contract violations should generally not crash it, while
C++ contract violations should.

2 files changed, 16 insertions, 2 deletions

diff --git a/backends/cxxrtl/cxxrtl.h b/backends/cxxrtl/cxxrtl.h
index 41089a153..7d3a8485c 100644
--- a/backends/cxxrtl/cxxrtl.h
+++ b/backends/cxxrtl/cxxrtl.h
@@ -53,6 +53,20 @@
 #define CXXRTL_ALWAYS_INLINE inline
 #endif
 
+// CXXRTL uses assert() to check for C++ contract violations (which may result in e.g. undefined behavior
+// of the simulation code itself), and CXXRTL_ASSERT to check for RTL contract violations (which may at
+// most result in undefined simulation results).
+//
+// Though by default, CXXRTL_ASSERT() expands to assert(), it may be overridden e.g. when integrating
+// the simulation into another process that should survive violating RTL contracts.
+#ifndef CXXRTL_ASSERT
+#ifndef CXXRTL_NDEBUG
+#define CXXRTL_ASSERT(x) assert(x)
+#else
+#define CXXRTL_ASSERT(x)
+#endif
+#endif
+
 namespace cxxrtl {
 
 // All arbitrary-width values in CXXRTL are backed by arrays of unsigned integers called chunks. The chunk size
diff --git a/backends/cxxrtl/cxxrtl_backend.cc b/backends/cxxrtl/cxxrtl_backend.cc
index a48ea5b23..23ea57b5a 100644
--- a/backends/cxxrtl/cxxrtl_backend.cc
+++ b/backends/cxxrtl/cxxrtl_backend.cc
@@ -1154,7 +1154,7 @@ struct CxxrtlWorker {
 				// larger program) will never crash the code that calls into it.
 				//
 				// If assertions are disabled, out of bounds reads are defined to return zero.
-				f << indent << "assert(" << valid_index_temp << ".valid && \"out of bounds read\");\n";
+				f << indent << "CXXRTL_ASSERT(" << valid_index_temp << ".valid && \"out of bounds read\");\n";
 				f << indent << "if(" << valid_index_temp << ".valid) {\n";
 				inc_indent();
 					if (writable_memories[memory]) {
@@ -1211,7 +1211,7 @@ struct CxxrtlWorker {
 				// See above for rationale of having both the assert and the condition.
 				//
 				// If assertions are disabled, out of bounds writes are defined to do nothing.
-				f << indent << "assert(" << valid_index_temp << ".valid && \"out of bounds write\");\n";
+				f << indent << "CXXRTL_ASSERT(" << valid_index_temp << ".valid && \"out of bounds write\");\n";
 				f << indent << "if (" << valid_index_temp << ".valid) {\n";
 				inc_indent();
 					f << indent << mangle(memory) << ".update(" << valid_index_temp << ".index, ";