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>

4 files changed, 35 insertions, 18 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)
diff --git a/source/slang/slang-emit-hlsl.cpp b/source/slang/slang-emit-hlsl.cpp
index 434f0803e..96b751789 100644
--- a/source/slang/slang-emit-hlsl.cpp
+++ b/source/slang/slang-emit-hlsl.cpp
@@ -1168,7 +1168,7 @@ void HLSLSourceEmitter::emitMeshOutputModifiersImpl(IRInst* varInst)
             : as<IRIndicesDecoration>(modifier)    ? "indices "
             : as<IRPrimitivesDecoration>(modifier) ? "primitives "
             : nullptr;
-        SLANG_EXPECT(s, "Unhandled type of mesh output decoration");
+        SLANG_ASSERT(s && "Unhandled type of mesh output decoration");
         m_writer->emit(s);
     }
 }
diff --git a/source/slang/slang-ir-glsl-legalize.cpp b/source/slang/slang-ir-glsl-legalize.cpp
index 8181deb1b..f6df7aa23 100644
--- a/source/slang/slang-ir-glsl-legalize.cpp
+++ b/source/slang/slang-ir-glsl-legalize.cpp
@@ -952,7 +952,7 @@ ScalarizedVal createSimpleGLSLGlobalVarying(
             // It's legal to declare these as unsized arrays, but by sizing
             // them by the (max) max size GLSL allows us to index into them
             // with variable index.
-            SLANG_EXPECT(dd->elementCount, "Mesh output declarator didn't specify element count");
+            SLANG_ASSERT(dd->elementCount && "Mesh output declarator didn't specify element count");
             auto arrayType = builder->getArrayType(type, dd->elementCount);
 
             IRArrayTypeLayout::Builder arrayTypeLayoutBuilder(builder, typeLayout);
@@ -1737,7 +1737,7 @@ void legalizeMeshOutputParam(
 {
     auto builder = context->getBuilder();
     auto stage = context->getStage();
-    SLANG_EXPECT(stage == Stage::Mesh, "legalizing mesh output, but we're not a mesh shader");
+    SLANG_ASSERT(stage == Stage::Mesh && "legalizing mesh output, but we're not a mesh shader");
     IRBuilderInsertLocScope locScope{builder};
     builder->setInsertInto(func);
 
@@ -1814,7 +1814,7 @@ void legalizeMeshOutputParam(
     traverseUsers(g, [&](IRInst* u)
     {
         auto l = as<IRLoad>(u);
-        SLANG_EXPECT(l, "Mesh Output sentinel parameter wasn't used in a load");
+        SLANG_ASSERT(l && "Mesh Output sentinel parameter wasn't used in a load");
 
         std::function<void(ScalarizedVal&, IRInst*)> assignUses =
             [&](ScalarizedVal& d, IRInst* a)
@@ -1838,7 +1838,7 @@ void legalizeMeshOutputParam(
                 if(auto m = as<IRFieldAddress>(s))
                 {
                     auto key = as<IRStructKey>(m->getField());
-                    SLANG_EXPECT(key, "Result of getField wasn't a struct key");
+                    SLANG_ASSERT(key && "Result of getField wasn't a struct key");
 
                     auto d_ = extractField(builder, d, kMaxUInt, key);
                     assignUses(d_, m);
@@ -1880,7 +1880,7 @@ void legalizeMeshOutputParam(
                     // best we can hope for without going and
                     // specializing foo.
                     auto ptr = as<IRPtrTypeBase>(a->getFullType());
-                    SLANG_EXPECT(ptr, "Mesh output parameter was passed by value");
+                    SLANG_ASSERT(ptr && "Mesh output parameter was passed by value");
                     auto t = ptr->getValueType();
                     auto tmp = builder->emitVar(t);
                     for(UInt i = 0; i < c->getOperandCount(); i++)
@@ -2045,7 +2045,7 @@ void legalizeMeshOutputParam(
         traverseUsers(builtin.param, [&](IRInst* u)
         {
             auto p = as<IRGetElementPtr>(u);
-            SLANG_EXPECT(p, "Mesh Output sentinel parameter wasn't used as an array");
+            SLANG_ASSERT(p && "Mesh Output sentinel parameter wasn't used as an array");
 
             IRBuilderInsertLocScope locScope{builder};
             builder->setInsertBefore(p);