Made array index warnings conditional on -Warray-index

Author: totalspectrum

cmdline.c

@@ -616,7 +616,7 @@ static FlagTable warnflag[] = {
     { "hide-members", WARN_HIDE_MEMBERS },
     { "init-vars", WARN_UNINIT_VARS },
     { "language-extensions", WARN_LANG_EXTENSIONS },
-    
+    { "array-index", WARN_ARRAY_INDEX },
     { "all", WARN_ALL },
 };
 

doc/general.md

@@ -253,13 +253,17 @@ function for "warn(!init-vars)" myfunc()
 
 Multiple warnings may be given, separated by commas. To turn a warning off, prefix it with `!` or with `~`. To enable all warnings, use the word `all`.
 
-Thus, a Spin function with `{++opt(!all,hide-members)}` will always be compiled with no warnings except for uninitialzed variables.
+Thus, a Spin function with `{++opt(!all,hide-members)}` will always be compiled with no warnings except for uninitialized variables.
 
 ### Warning control on the command line
 
 Multiple `-W` options may be given, or combined separated by commas. So for example to compile with all warnings except uninitialized variables, one would give `-Wall,!init-vars`.
 
 
+### Array index warnings (-Warray-index) (enabled by default)
+
+Warns when a constant array index is out of range. Note that this only applies to explicit constants; the warning will not be issued for computed indices, even when the computation is "obvious".
+
 ### Assembler usage warnings (-Wasm-usage) (enabled by default)
 
 Warns about some common issues in assembly code, for example forgetting to put `wc` or `wz` on a `cmp` instruction. This option is only available on the command line, it is generally ignored on a per-function basis (even for functions with inline assembly) because assembly parsing is handled specially.

frontends/common.h

@@ -213,10 +213,11 @@ extern int gl_warn_flags;     /* flags for warnings */
 #define WARN_ASM_USAGE          0x000004
 #define WARN_UNINIT_VARS        0x000008
 #define WARN_C_CONST_STRING     0x000010
+#define WARN_ARRAY_INDEX        0x000020
 #define WARN_ASM_FIRST_PASS     0x800000      
 #define WARN_ALL                0xFFFFFF
 
-#define DEFAULT_WARN_FLAGS (WARN_ASM_USAGE | WARN_UNINIT_VARS | WARN_ASM_FIRST_PASS)
+#define DEFAULT_WARN_FLAGS (WARN_ASM_USAGE | WARN_UNINIT_VARS | WARN_ASM_FIRST_PASS | WARN_ARRAY_INDEX)
 
 extern int gl_list_options;   /* options for listing files */
 #define LIST_INCLUDE_CONSTANTS  0x0001

frontends/types.c

@@ -1971,16 +1971,18 @@ static AST *doCheckTypes(AST *ast)
             if (IsConstExpr(ast->right)) {
                 int idx = EvalConstExpr(ast->right);
                 int low = 0;
+                unsigned warn_flags = curfunc ? curfunc->warn_flags : gl_warn_flags;
                 if (!base || IsConstExpr(base)) {
                     low = base ? EvalConstExpr(base) : 0;
-                    if (idx < low) {
+                    if (idx < low && 0 != (warn_flags & WARN_ARRAY_INDEX)) {
                         WARNING(ast, "Array index %d is less than array start (%d)", idx, low);
                     }
                 }
                 AST *aSize = GetArraySize(lefttype);
                 if (IsConstExpr(aSize)) {
-                    int high = EvalConstExpr(aSize) + low - 1;
-                    if (idx > high) {
+                    int len = EvalConstExpr(aSize);
+                    int high = len + low - 1;
+                    if (idx > high && len > 0 && 0 != (warn_flags & WARN_ARRAY_INDEX)) {
                         WARNING(ast, "Array index %d is above end of array (%d)", idx, high);
                     }
                 }