Asserts: Use lambdas to keep assertion code away from the main code path

src/common/assert.h

@@ -4,24 +4,43 @@
 
 #pragma once
 
+#include <cstdlib>
+
 #include "common/common_funcs.h"
 
+// For asserts we'd like to keep all the junk executed when an assert happens away from the
+// important code in the function. One way of doing this is to put all the relevant code inside a
+// lambda and force the compiler to not inline it. Unfortunately, MSVC seems to have no syntax to
+// specify __declspec on lambda functions, so what we do instead is define a noinline wrapper
+// template that calls the lambda. This seems to generate an extra instruction at the call-site
+// compared to the ideal implementation (which wouldn't support ASSERT_MSG parameters), but is good
+// enough for our purposes.
+template <typename Fn>
+#if defined(_MSC_VER)
+    __declspec(noinline, noreturn)
+#elif defined(__GNUC__)
+    __attribute__((noinline, noreturn, cold))
+#endif
+static void assert_noinline_call(const Fn& fn) {
+    fn();
+    Crash();
+    exit(1); // Keeps GCC's mouth shut about this actually returning
+}
+
 // TODO (yuriks) allow synchronous logging so we don't need printf
 #define ASSERT(_a_) \
-    do if (!(_a_)) {\
+    do if (!(_a_)) { assert_noinline_call([] { \
         fprintf(stderr, "Assertion Failed!\n\n  Line: %d\n  File: %s\n  Time: %s\n", \
                      __LINE__, __FILE__, __TIME__); \
-        Crash(); \
-    } while (0)
+    }); } while (0)
 
 #define ASSERT_MSG(_a_, ...) \
-    do if (!(_a_)) {\
+    do if (!(_a_)) { assert_noinline_call([&] { \
         fprintf(stderr, "Assertion Failed!\n\n  Line: %d\n  File: %s\n  Time: %s\n", \
                      __LINE__, __FILE__, __TIME__); \
         fprintf(stderr, __VA_ARGS__); \
         fprintf(stderr, "\n"); \
-        Crash(); \
-    } while (0)
+    }); } while (0)
 
 #define UNREACHABLE() ASSERT_MSG(false, "Unreachable code!")