compiler: improve Value handling and expression evaluator

AST values:
* add `getValue()` type methods for literal expr nodes, returning a `Value`
* add `Value.castAs()` type method
* add `ValueKind.Error` for invalid result and evaluation errors
* add `Value` factories for unsigned, signed, float, boolean and error

Simplify ctv_analyser:
* remove hard coded strings in `Limits` array
* dispatch to more `getValue()` handlers
* improve conversion checker: refine arithmetic operations
* use expression evaluator from ast_evaluator for Ctv expressions

Expression/Function evaluator:
* add statement evaluator
* move generator/c/c_generator_pure_call.c2 to ast/ast_evaluator.c2
* add function address to evaluate some external function calls
* support indirect pure functions calls including recursive and external

Improve C generator:
* add `Generator.need_const_expr`, used for static intializers
* add `Generator.emitConstExpr()` to force pure function calls evaluation
* simplify initializer generation
* pass Diags object for code generation errors

Author: chqrlie

analyser/conversion_checker_expr.c2

@@ -23,19 +23,17 @@ type ExprWidth struct {
     bool is_signed;
 }
 
-fn ExprWidth ExprWidth.mergeSmaller(ExprWidth* w1, ExprWidth* w2) {
+fn ExprWidth ExprWidth.mergeSmaller(ExprWidth w1, ExprWidth w2) {
     ExprWidth result;
-    if (w2.width < w1.width) result.width = w2.width;
-    else result.width = w1.width;
-    result.is_signed = w1.is_signed || w2.is_signed;
+    result.width = (w1.width < w2.width) ? w1.width : w2.width;
+    result.is_signed = w1.is_signed | w2.is_signed;
     return result;
 }
 
-fn ExprWidth ExprWidth.mergeWider(ExprWidth* w1, ExprWidth* w2) {
+fn ExprWidth ExprWidth.mergeWider(ExprWidth w1, ExprWidth w2) {
     ExprWidth result;
-    if (w2.width > w1.width) result.width = w2.width;
-    else result.width = w1.width;
-    result.is_signed = w1.is_signed || w2.is_signed;
+    result.width = (w1.width > w2.width) ? w1.width : w2.width;
+    result.is_signed = w1.is_signed | w2.is_signed;
     return result;
 }
 
@@ -44,13 +42,8 @@ fn ExprWidth getExprWidth(const Expr* e) {
 
     if (e.isCtv()) {
         Value v = ctv_analyser.get_value(e);
-        if (v.isNegative()) {
-            result.width = v.getWidth();
-            result.is_signed = true;
-        } else {
-            result.width = v.getWidth();
-            result.is_signed = false;
-        }
+        result.width = v.getWidth();
+        result.is_signed = v.isNegative();
         return result;
     }
 
@@ -63,26 +56,13 @@ fn ExprWidth getExprWidth(const Expr* e) {
     case Nil:
         break;
     case Identifier:
-        QualType qt = e.getType();
-        qt = qt.getCanonicalType();
-        if (qt.isBuiltin()) {
-            BuiltinType* bi = qt.getBuiltin();
-            result.width = cast<u8>(bi.getWidth());
-            result.is_signed = bi.isSigned();
-        } else {
-            // pointer or something
-            result.width = cast<u8>(ast.getWordSize() * 8);
-            result.is_signed = true;
-        }
-        return result;
+        return getTypeWidth(e.getType());
     case Type:
         break;
     case Call:
         return getTypeWidth(e.getType());
     case InitList:
-        break;
     case FieldDesignatedInit:
-        break;
     case ArrayDesignatedInit:
         break;
     case BinaryOperator:
@@ -92,27 +72,19 @@ fn ExprWidth getExprWidth(const Expr* e) {
     case ConditionalOperator:
         return getCondOpWidth(cast<ConditionalOperator*>(e));
     case Builtin:
+        // TODO ToContainer -> width = 64
         break;
     case ArraySubscript:
+        // TODO BitOffset -> specific width
     case Member:
-        QualType qt = e.getType();
-        qt = qt.getCanonicalType();
-        if (qt.isPointer()) {
-            result.width = 64; // TODO or 32
-            result.is_signed = false;
-            return result;
-        }
-        assert(qt.isBuiltin());
-        BuiltinType* bi = qt.getBuiltin();
-        result.width = cast<u8>(bi.getWidth());
-        result.is_signed = bi.isSigned();
-        return result;
+        return getTypeWidth(e.getType());
     case Paren:
         const ParenExpr* p = cast<ParenExpr*>(e);
         return getExprWidth(p.getInner());
     case BitOffset:
         break;
     case ExplicitCast:
+        // TODO: explicit cast may reduce signed values
         QualType qt = e.getType();
         qt = qt.getCanonicalType();
         assert(qt.isBuiltin());
@@ -127,7 +99,7 @@ fn ExprWidth getExprWidth(const Expr* e) {
         RangeExpr* b = cast<RangeExpr*>(e);
         ExprWidth lhs = getExprWidth(b.getLHS());
         ExprWidth rhs = getExprWidth(b.getRHS());
-        return ExprWidth.mergeWider(&lhs, &rhs);
+        return ExprWidth.mergeWider(lhs, rhs);
     }
 
     e.dump();
@@ -138,7 +110,7 @@ fn ExprWidth getExprWidth(const Expr* e) {
 fn ExprWidth getCondOpWidth(const ConditionalOperator* c) {
     ExprWidth lhs = getExprWidth(c.getLHS());
     ExprWidth rhs = getExprWidth(c.getRHS());
-    return ExprWidth.mergeWider(&lhs, &rhs);
+    return ExprWidth.mergeWider(lhs, rhs);
 }
 
 fn ExprWidth getUnaryOpWidth(const UnaryOperator* u) {
@@ -183,37 +155,36 @@ fn ExprWidth getBinOpWidth(const BinaryOperator* b) {
     case Multiply:
         break;
     case Divide:
-        break;
+        return getExprWidth(b.getLHS());
     case Remainder:
-        // TODO special
-        break;
+        return getExprWidth(b.getRHS());
     case Add:
-        break;
     case Subtract:
         break;
     case ShiftLeft:
-        break;
+        ExprWidth result = getExprWidth(b.getLHS());
+        if (result.width < 31) { result.width = 31; result.is_signed = true; }
+        return result;
     case ShiftRight:
-        break;
+        return getExprWidth(b.getLHS());
     case LessThan:
     case GreaterThan:
     case LessEqual:
     case GreaterEqual:
     case Equal:
     case NotEqual:
-        ExprWidth result = { 1, 0 }
+        ExprWidth result = { .width = 1, .is_signed = false }
         return result;
     case And:
         ExprWidth l = getExprWidth(b.getLHS());
         ExprWidth r = getExprWidth(b.getRHS());
-        return ExprWidth.mergeSmaller(&l, &r);
+        return ExprWidth.mergeSmaller(l, r);
     case Xor:
-        break;
     case Or:
         break;
     case LAnd:
     case LOr:
-        ExprWidth result = { 1, 0 }
+        ExprWidth result = { .width = 1, .is_signed = false }
         return result;
     case Assign:
     case MulAssign:
@@ -226,25 +197,29 @@ fn ExprWidth getBinOpWidth(const BinaryOperator* b) {
     case AndAssign:
     case XorAssign:
     case OrAssign:
+        // TODO: refine this
         return getExprWidth(b.getLHS());
     }
 
     ExprWidth lhs = getExprWidth(b.getLHS());
     ExprWidth rhs = getExprWidth(b.getRHS());
-    return ExprWidth.mergeWider(&lhs, &rhs);
+    return ExprWidth.mergeWider(lhs, rhs);
 }
 
 fn ExprWidth getTypeWidth(QualType qt) {
-    if (qt.isPointer()) {
-        // TODO or 32
-        ExprWidth result = { .width = 64, .is_signed = false }
+    qt = qt.getCanonicalType();
+    if (qt.isEnum()) {
+        EnumType* et = qt.getEnumType();
+        qt = et.getImplType();
+    }
+    if (qt.isBuiltin()) {
+        const BuiltinType* bi = qt.getBuiltin();
+        ExprWidth result = { .width = cast<u8>(bi.getWidth()), .is_signed = bi.isSigned() }
         return result;
     }
-    assert(qt.isBuiltin());
-    const BuiltinType* bi = qt.getBuiltin();
-    ExprWidth result;
-    result.width = cast<u8>(bi.getWidth());
-    result.is_signed = bi.isSigned();
+    // pointer or something
+    // TODO or 32
+    ExprWidth result = { .width = cast<u8>(ast.getWordSize() * 8), .is_signed = false }
     return result;
 }