Handle for loops with constant indices but byte or word variables

Author: totalspectrum

Changelog.txt

@@ -1,6 +1,7 @@
 Version 6.6.2
 - Added warning (-Warray-index) for constant array indices out of bounds
 - Allow warnings and optimizations to be turned off with a `no-` prefix (so `warn(no-init-vars)` is like `warn(!init-vars)`).
+- Added some peephole optimizations to remove unnecessary sign extension
 
 Version 6.6.1
 - Changed type of `dat` array in C++ output to `unsigned char`

Test/Expect/stest305.pasm

@@ -0,0 +1,21 @@
+pub main
+  coginit(0, @entry, 0)
+dat
+	org	0
+entry
+
+_blah
+	rdword	_var01, arg01
+	and	_var01, #7
+	wrword	_var01, arg01
+_blah_ret
+	ret
+
+COG_BSS_START
+	fit	496
+	org	COG_BSS_START
+_var01
+	res	1
+arg01
+	res	1
+	fit	496

Test/stest305.c

@@ -0,0 +1,3 @@
+void blah(short *x) {
+    *x &= 7;
+}

loops.c

@@ -1030,9 +1030,25 @@ CheckSimpleIncrementLoop(AST *stmt)
     } else {
         return;
     }
-    if (!AstMatchName(updateVar, condtest->left))
-        return;
-
+    if (!AstMatchName(updateVar, condtest->left)) {
+        // special case sign extension
+        bool isOK = false;
+        if (condtest->left && condtest->left->kind == AST_OPERATOR && (condtest->left->d.ival == K_SIGNEXTEND || condtest->left->d.ival == K_ZEROEXTEND) ) {
+            if (IsConstExpr(condtest->left->right) && AstMatchName(updateVar, condtest->left->left) && IsConstExpr(finalValue)) {
+                int32_t finalVal = EvalConstExpr(finalValue);
+                int32_t extendVal = EvalConstExpr(condtest->left->right);
+                extendVal = 1<<(extendVal & 0x1f);
+                if (condtest->left->d.ival == K_SIGNEXTEND) {
+                    extendVal = extendVal >> 1;
+                }
+                isOK = (finalVal >= 0) &&  (finalVal < extendVal);
+            }
+        }
+        if (!isOK) {
+            return;
+        }
+    }
+    
     /* check that the update is i++, and the variable is not used anywhere else */
     while (update->kind == AST_SEQUENCE) {
         if (AstUsesName(update->right, updateVar)) {