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Support taking extern pointers at comptime

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This commit makes it possible to obtain pointers to `extern` variables
at comptime.

 - `ir_get_var_ptr` employs several checks to determine if the given
   variable is eligible for obtaining its pointer at comptime. This
   commit alters these checks to consider `extern` variables, which have
   runtime values, as eligible.

 - After this change, it's now possible for `render_const_val` to be
   called for `extern` variables. This commit modifies
   `render_const_val` to suppress the value generation for `extern`
   variables.

 - `do_code_gen` now creates `ZigValue::llvm_global` of `extern`
   variables before iterating through module-level variables so that
   other module-level variables can refer to them.

This solution is incomplete since there are several cases still
failing:

 - `global_var.array[n..m]`
 - `&global_var.array[i]`
 - `&global_var.inner_struct.value`
 - `&global_array[i]`

Closes #5349
This commit is contained in:
yvt
2020-05-15 18:28:58 +09:00
committed by Andrew Kelley
parent 3b26e50863
commit d3ebd42865
8 changed files with 284 additions and 47 deletions
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70
src/codegen.cpp
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@@ -7754,6 +7754,13 @@ static LLVMValueRef gen_const_val(CodeGen *g, ZigValue *const_val, const char *n
}
static void render_const_val(CodeGen *g, ZigValue *const_val, const char *name) {
if (const_val->special == ConstValSpecialRuntime) {
// `const_val` refers to an extern variable. Don't generate an `LLVMValueRef` for
// the variable. We shouldn't call `LLVMSetInitializer` on it either.
assert(const_val->llvm_global);
return;
}
if (!const_val->llvm_value)
const_val->llvm_value = gen_const_val(g, const_val, name);
@@ -7762,6 +7769,13 @@ static void render_const_val(CodeGen *g, ZigValue *const_val, const char *name)
}
static void render_const_val_global(CodeGen *g, ZigValue *const_val, const char *name) {
if (const_val->special == ConstValSpecialRuntime) {
// `const_val` refers to an extern variable. `llvm_global` should already
// have been created by an earlier codegen pass.
assert(const_val->llvm_global);
return;
}
if (!const_val->llvm_global) {
LLVMTypeRef type_ref = const_val->llvm_value ?
LLVMTypeOf(const_val->llvm_value) : get_llvm_type(g, const_val->type);
@@ -7891,6 +7905,39 @@ static void do_code_gen(CodeGen *g) {
generate_error_name_table(g);
// Create extern variables
for (size_t i = 0; i < g->global_vars.length; i += 1) {
TldVar *tld_var = g->global_vars.at(i);
ZigVar *var = tld_var->var;
bool externally_initialized = var->decl_node->data.variable_declaration.expr == nullptr;
if (!externally_initialized) {
continue;
}
assert(var->decl_node->data.variable_declaration.is_extern);
const char *symbol_name = var->name;
LLVMValueRef global_value;
LLVMValueRef existing_llvm_var = LLVMGetNamedGlobal(g->module, symbol_name);
if (existing_llvm_var) {
global_value = LLVMConstBitCast(existing_llvm_var,
LLVMPointerType(get_llvm_type(g, var->var_type), 0));
} else {
global_value = LLVMAddGlobal(g->module, get_llvm_type(g, var->var_type), symbol_name);
// TODO debug info for the extern variable
LLVMSetLinkage(global_value, LLVMExternalLinkage);
maybe_import_dll(g, global_value, GlobalLinkageIdStrong);
LLVMSetAlignment(global_value, var->align_bytes);
LLVMSetGlobalConstant(global_value, var->gen_is_const);
set_global_tls(g, var, global_value);
}
var->value_ref = global_value;
var->const_value->llvm_global = global_value;
}
// Generate module level variables
for (size_t i = 0; i < g->global_vars.length; i += 1) {
TldVar *tld_var = g->global_vars.at(i);
@@ -7956,28 +8003,12 @@ static void do_code_gen(CodeGen *g) {
linkage = global_export->linkage;
}
LLVMValueRef global_value;
bool externally_initialized = var->decl_node->data.variable_declaration.expr == nullptr;
if (externally_initialized) {
LLVMValueRef existing_llvm_var = LLVMGetNamedGlobal(g->module, symbol_name);
if (existing_llvm_var) {
global_value = LLVMConstBitCast(existing_llvm_var,
LLVMPointerType(get_llvm_type(g, var->var_type), 0));
} else {
global_value = LLVMAddGlobal(g->module, get_llvm_type(g, var->var_type), symbol_name);
// TODO debug info for the extern variable
LLVMSetLinkage(global_value, to_llvm_linkage(linkage));
maybe_import_dll(g, global_value, GlobalLinkageIdStrong);
LLVMSetAlignment(global_value, var->align_bytes);
LLVMSetGlobalConstant(global_value, var->gen_is_const);
set_global_tls(g, var, global_value);
}
} else {
if (!externally_initialized) {
bool exported = (linkage != GlobalLinkageIdInternal);
render_const_val(g, var->const_value, symbol_name);
render_const_val_global(g, var->const_value, symbol_name);
global_value = var->const_value->llvm_global;
LLVMValueRef global_value = var->const_value->llvm_global;
if (exported) {
LLVMSetLinkage(global_value, to_llvm_linkage(linkage));
@@ -7997,10 +8028,9 @@ static void do_code_gen(CodeGen *g) {
LLVMSetGlobalConstant(global_value, var->gen_is_const);
set_global_tls(g, var, global_value);
var->value_ref = global_value;
}
var->value_ref = global_value;
for (size_t export_i = 1; export_i < var->export_list.length; export_i += 1) {
GlobalExport *global_export = &var->export_list.items[export_i];
LLVMAddAlias(g->module, LLVMTypeOf(var->value_ref), var->value_ref, buf_ptr(&global_export->name));