optimized some BASIC string expressions

Author: totalspectrum

Changelog.txt

@@ -3,6 +3,7 @@ Version 6.1.6
 - Implemented flush() for FATFS files (thanks to Ada)
 - Improved some error messages
 - In C++ output, treat unknown types in prints as generic
+- Optimized a few BASIC string expressions 
 - Revised BASIC use of + operator on strings
 
 Version 6.1.5

ast.c

@@ -519,9 +519,63 @@ AstStringLen(AST *list)
         }
         list = list->right;
     }
+    if (list && list->kind == AST_STRING) {
+        len += strlen(list->d.string);
+    }
     return len;
 }
 
+static char *
+CopyString(char *p, AST *list)
+{
+    list = list->left;
+    while (list && list->kind == AST_EXPRLIST) {
+        if (!list->left) continue;
+        if (list->left->kind == AST_STRING) {
+            strcpy(p, list->left->d.string);
+            p += strlen(list->left->d.string);
+        } else {
+            *p++ = list->left->d.ival;
+        }
+        list = list->right;
+    }
+    if (list && list->kind == AST_STRING) {
+        strcpy(p, list->d.string);
+        p += strlen(list->d.string);
+    }
+    return p;
+}
+
+/* merge two AST string pointers */
+AST *
+AstMergeStrings(AST *left, AST *right)
+{
+    int newLen = 1;
+    if (left) {
+        if (left->kind != AST_STRINGPTR) {
+            ERROR(left, "Internal errors, expected string");
+            return left;
+        }
+        newLen += AstStringLen(left);
+    }
+    if (right) {
+        if (right->kind != AST_STRINGPTR) {
+            ERROR(right, "Internal errors, expected string");
+            return left;
+        }
+        newLen += AstStringLen(right);
+    }
+    char *newBuf = malloc(newLen);
+    char *p = newBuf;
+    if (left) {
+        p = CopyString(p, left);
+    }
+    if (right) {
+        p = CopyString(p, right);
+    }
+    return AstStringPtr(newBuf);
+}
+
 /* return length of an AST list; data is on left, ptr to next on right */
 int
 AstListLen(AST *list)

ast.h

@@ -309,6 +309,9 @@ int AstListLen(AST *a);
 /* length of an AST stringptr list */
 int AstStringLen(AST *a);
 
+/* merge two AST string lists */
+AST *AstMergeStrings(AST *lhs, AST *rhs);
+
 /* mark new ASTs to be created to have the same line as AST old */
 /* used when we're transforming ASTs */
 void AstReportAs(AST *old, ASTReportInfo *save);

frontends/basic/basiclang.c

@@ -924,12 +924,25 @@ doBasicTransform(AST **astptr, bool transformFuncall)
     case AST_FUNCCALL:
         doBasicTransform(&ast->left, transformFuncall);
         doBasicTransform(&ast->right, transformFuncall);
-        if (transformFuncall)
-        {
+        if (transformFuncall) {
             // the parser treats a(x) as a function call (always), but in
             // fact it may be an array reference; change it to one if applicable
             adjustFuncCall(ast);
         }
+        // check for some special cases like chr$(65)
+        if (ast->kind == AST_FUNCCALL && IsIdentifier(ast->left)) {
+            const char *funcName = GetIdentifierName(ast->left);
+            if (!strcasecmp(funcName, "chr$")) {
+                AST *arg = ast->right->left;
+                if (arg && ast->right->right == NULL && IsConstExpr(arg)) {
+                    int n = EvalConstExpr(arg);
+                    char *s = malloc(2);
+                    s[0] = n;
+                    s[1] = 0;
+                    *ast = *AstStringPtr(s);
+                }
+            }
+        }
         break;
     case AST_METHODREF:
         doBasicTransform(&ast->left, transformFuncall);

frontends/types.c

@@ -162,7 +162,14 @@ MakeOperatorCall(AST *func, AST *left, AST *right, AST *extraArg)
     if (extraArg) {
         params = AddToList(params, NewAST(AST_EXPRLIST, extraArg, NULL));
     }
-    call = NewAST(AST_FUNCCALL, func, params);
+
+    // do some optimizations on constant values
+    if (func == string_concat && left && right && left->kind == AST_STRINGPTR && right->kind == AST_STRINGPTR)
+    {
+        call = AstMergeStrings(left, right);
+    } else {
+        call = NewAST(AST_FUNCCALL, func, params);
+    }
     AstReportDone(&saveinfo);
     return call;
 }