Add SLANG_ASSUME and use it in release asserts (#2859)

* Remove UNREACHABLE

* formatting

* Remove unused SLANG_EXPECT macros

* Add SLANG_ASSUME and use it in release asserts

* Reassure GCC that we are using memcpy responsibly

---------

Co-authored-by: Yong He <yonghe@outlook.com>

2 files changed, 28 insertions, 11 deletions

diff --git a/source/core/slang-common.h b/source/core/slang-common.h
index cd1490a20..5cf0432f2 100644
--- a/source/core/slang-common.h
+++ b/source/core/slang-common.h
@@ -76,28 +76,43 @@ namespace Slang
     template <typename T>
     SLANG_FORCE_INLINE T* clone(IClonable* clonable) { return (T*)clonable->clone(T::getTypeGuid()); }
 
+}
 
 // TODO: Shouldn't these be SLANG_ prefixed?
 #ifdef _MSC_VER
 #define UNREACHABLE_RETURN(x)
-#define UNREACHABLE(x)
 #else
 #define UNREACHABLE_RETURN(x) return x;
-#define UNREACHABLE(x) x;
 #endif
 
-}
+//
+// Use `SLANG_ASSUME(myBoolExpression);` to inform the compiler that the condition is true.
+// Do not rely on side effects of the condition being performed.
+//
+#if defined(__cpp_assume)
+#    define SLANG_ASSUME(X) [[assume(X)]]
+#elif SLANG_GCC
+#    define SLANG_ASSUME(X) do{if(!(X)) __builtin_unreachable();} while(0)
+#elif SLANG_CLANG
+#    define SLANG_ASSUME(X) __builtin_assume(X)
+#elif SLANG_VC
+#    define SLANG_ASSUME(X) __assume(X)
+#else
+     [[noreturn]] inline void invokeUndefinedBehaviour() {}
+#    define SLANG_ASSUME(X) do{if(!(X)) invokeUndefinedBehaviour();} while(0)
+#endif
 
+//
+// Assertions abort in debug builds, but inform the compiler of true
+// assumptions in release builds
+//
 #ifdef _DEBUG
-#define SLANG_EXPECT(VALUE, MSG) if(VALUE) {} else SLANG_ASSERT_FAILURE(MSG)
-#define SLANG_ASSERT(VALUE) SLANG_EXPECT(VALUE, #VALUE)
+#define SLANG_ASSERT(VALUE) do{if(!(VALUE)) SLANG_ASSERT_FAILURE(#VALUE);} while(0)
 #else
-#define SLANG_EXPECT(VALUE, MSG) do {} while(0)
-#define SLANG_ASSERT(VALUE) do {} while(0)
+#define SLANG_ASSERT(VALUE) SLANG_ASSUME(VALUE)
 #endif
 
 #define SLANG_RELEASE_ASSERT(VALUE) if(VALUE) {} else SLANG_ASSERT_FAILURE(#VALUE)
-#define SLANG_RELEASE_EXPECT(VALUE, WHAT) if(VALUE) {} else SLANG_UNEXPECTED(WHAT)
 
 template<typename T> void slang_use_obj(T&) {}
 
diff --git a/source/core/slang-io.cpp b/source/core/slang-io.cpp
index 81f0cbf87..8a2243b15 100644
--- a/source/core/slang-io.cpp
+++ b/source/core/slang-io.cpp
@@ -124,9 +124,11 @@ namespace Slang
         builder << "/tmp/" << inPrefix << "-XXXXXX";
 
         List<char> buffer;
-        buffer.setCount(builder.getLength() + 1);
-        ::memcpy(buffer.getBuffer(), builder.getBuffer(), builder.getLength());
-        buffer[builder.getLength()] = 0;
+        auto copySize = builder.getLength();
+        buffer.setCount(copySize + 1);
+        SLANG_ASSERT(copySize < PTRDIFF_MAX); // Shhh gcc, it's ok, we're not copying 9000 Petabytes
+        ::memcpy(buffer.getBuffer(), builder.getBuffer(), copySize);
+        buffer[copySize] = 0;
 
         int handle = mkstemp(buffer.getBuffer());
         if (handle == -1)