simd fix; generator fix

src/llvm_abi.cpp

@@ -726,13 +726,19 @@ namespace lbAbiAmd64SysV {
 	gb_internal bool is_aggregate(LLVMTypeRef type) {
 		// A single-member wrapper is passed like its member, but only while that
 		// member still fits one eightbyte. `struct{i128}` needs two registers and
-		// goes to memory when they are gone, where a bare `i128` does not -- clang
-		// emits `byval align 16` for the struct and a plain `i128` for the scalar.
+		// goes to memory when they are gone. A bare `i128` does not; clang emits
+		// `byval align 16` for the struct and a plain `i128` for the scalar.
 		LLVMTypeKind kind = LLVMGetTypeKind(type);
 		switch (kind) {
 		case LLVMStructTypeKind:
 			if (LLVMCountStructElementTypes(type) == 1) {
 				LLVMTypeRef elem = LLVMStructGetTypeAtIndex(type, 0);
+				// A VECTOR member keeps the wrapper an aggregate whatever its size:
+				// LLVM gives a vector its own oversized stack slot, so an unwrapped
+				// `struct{#simd[2]f32}` takes 16 bytes where the ABI wants 8.
+				if (LLVMGetTypeKind(elem) == LLVMVectorTypeKind) {
+					return true;
+				}
 				return lb_sizeof(elem) > 8 || is_aggregate(elem);
 			}
 			return true;