Correct debug information logic for procedure parameters

src/llvm_backend.hpp

@@ -232,6 +232,7 @@ struct lbTargetList {
 
 enum lbProcedureFlag : u32 {
 	lbProcedureFlag_WithoutMemcpyPass = 1<<0,
+	lbProcedureFlag_DebugAllocaCopy = 1<<1,
 };
 
 struct lbCopyElisionHint {

src/llvm_backend_debug.cpp

@@ -965,6 +965,77 @@ void lb_add_debug_local_variable(lbProcedure *p, LLVMValueRef ptr, Type *type, T
 	LLVMDIBuilderInsertDeclareBefore(m->debug_builder, storage, var_info, llvm_expr, llvm_debug_loc, instr);
 }
 
+
+void lb_add_debug_param_variable(lbProcedure *p, LLVMValueRef ptr, Type *type, Token const &token, unsigned arg_number) {
+	if (p->debug_info == nullptr) {
+		return;
+	}
+	if (type == nullptr) {
+		return;
+	}
+	if (type == t_invalid) {
+		return;
+	}
+	if (p->body == nullptr) {
+		return;
+	}
+
+	lbModule *m = p->module;
+	String const &name = token.string;
+	if (name == "" || name == "_") {
+		return;
+	}
+
+	if (lb_get_llvm_metadata(m, ptr) != nullptr) {
+		// Already been set
+		return;
+	}
+
+
+	AstFile *file = p->body->file();
+
+	LLVMMetadataRef llvm_scope = lb_get_current_debug_scope(p);
+	LLVMMetadataRef llvm_file = lb_get_llvm_metadata(m, file);
+	GB_ASSERT(llvm_scope != nullptr);
+	if (llvm_file == nullptr) {
+		llvm_file = LLVMDIScopeGetFile(llvm_scope);
+	}
+
+	if (llvm_file == nullptr) {
+		return;
+	}
+
+	LLVMDIFlags flags = LLVMDIFlagZero;
+	LLVMBool always_preserve = build_context.optimization_level == 0;
+
+	LLVMMetadataRef debug_type = lb_debug_type(m, type);
+
+	LLVMMetadataRef var_info = LLVMDIBuilderCreateParameterVariable(
+		m->debug_builder, llvm_scope,
+		cast(char const *)name.text, cast(size_t)name.len,
+		arg_number,
+		llvm_file, token.pos.line,
+		debug_type,
+		always_preserve, flags
+	);
+
+	LLVMValueRef storage = ptr;
+	LLVMValueRef instr = ptr;
+	LLVMBasicBlockRef block = p->decl_block->block;
+	LLVMMetadataRef llvm_debug_loc = lb_debug_location_from_token_pos(p, token.pos);
+	LLVMMetadataRef llvm_expr = LLVMDIBuilderCreateExpression(m->debug_builder, nullptr, 0);
+	lb_set_llvm_metadata(m, ptr, llvm_expr);
+	if (LLVMIsAAllocaInst(instr)) {
+		LLVMDIBuilderInsertDeclareBefore(m->debug_builder, storage, var_info, llvm_expr, llvm_debug_loc, instr);
+	} else {
+		// NOTE(bill, 2022-02-01): For parameter values, you must insert them at the end of the decl block
+		// The reason is that if the parameter is at index 0 and a pointer, there is not such things as an
+		// instruction "before" it.
+		LLVMDIBuilderInsertDeclareAtEnd(m->debug_builder, storage, var_info, llvm_expr, llvm_debug_loc, block);
+	}
+}
+
+
 void lb_add_debug_context_variable(lbProcedure *p, lbAddr const &ctx) {
 	if (!p->debug_info || !p->body) {
 		return;

src/llvm_backend_proc.cpp

@@ -473,6 +473,8 @@ void lb_begin_procedure_body(lbProcedure *p) {
 				}
 
 				lbArgType *arg_type = &ft->args[param_index];
+				defer (param_index += 1);
+
 				if (arg_type->kind == lbArg_Ignore) {
 					continue;
 				} else if (arg_type->kind == lbArg_Direct) {
@@ -487,20 +489,19 @@ void lb_begin_procedure_body(lbProcedure *p) {
 						param.type = e->type;
 
 						lbValue ptr = lb_address_from_load_or_generate_local(p, param);
+						GB_ASSERT(LLVMIsAAllocaInst(ptr.value));
 						lb_add_entity(p->module, e, ptr);
-						// lb_add_debug_local_variable(p, ptr.value, e->type, e->token);
+						lb_add_debug_param_variable(p, ptr.value, e->type, e->token, param_index+1);
 					}
 				} else if (arg_type->kind == lbArg_Indirect) {
 					if (e->token.string.len != 0 && !is_blank_ident(e->token.string)) {
 						lbValue ptr = {};
 						ptr.value = LLVMGetParam(p->value, param_offset+param_index);
 						ptr.type = alloc_type_pointer(e->type);
-
 						lb_add_entity(p->module, e, ptr);
-						// lb_add_debug_local_variable(p, ptr.value, e->type, e->token);
+						lb_add_debug_param_variable(p, ptr.value, e->type, e->token, param_index+1);
 					}
 				}
-				param_index += 1;
 			}
 		}