str[index] and list[index] done

src/main/java/chocopy/pa3/CodeGenImpl.java

@@ -967,8 +967,52 @@ public class CodeGenImpl extends CodeGenBase {
             return null;
         }
 
+        @Override
+        public Void analyze(IndexExpr node) {
+            node.list.dispatch(this);
+            node.index.dispatch(this);
+            RiscVBackend.Register listReg = T6, indexReg = T5, lenReg = A7;
+            betterBackend.emitPop(indexReg, "IndexExpr: Get Index");
+            betterBackend.emitPop(listReg, "IndexExpr: Get List/str ptr");
+            backend.emitLW(lenReg, listReg, 3*backend.getWordSize(), "IndexExpr: Get List/str length");
+            backend.emitADDI(listReg, listReg, 4*backend.getWordSize(), "IndexExpr: listPtr = list.data");
+
+            String labelPrefix = getLabelPrefix();
+            Label skipTranslateNegIndex = new Label(labelPrefix + ".fuckNegIndexEnd");
+
+            // Get real index.
+            backend.emitBGEZ(indexReg, skipTranslateNegIndex, "IndexExpr: Skip neg index op");
+            backend.emitADD(indexReg, indexReg, lenReg, "IndexExpr: Add length to negative index.");
+            backend.emitBLTZ(indexReg, errorOob, "IndexExpr: Exception: negative index still negative after adding length. FUCK IT!!!");
+
+            backend.emitLocalLabel(skipTranslateNegIndex, "IndexExpr: DO REAL ACCESS");
+            // Do real access!
+            backend.emitBGE(indexReg, lenReg, errorOob, "IndexExpr: Exception: index larger than length. FUCK IT.");
+            if(!node.list.getInferredType().equals(SymbolType.STR_TYPE)) {
+                assert backend.getWordSize() == 4;
+                backend.emitSLLI(indexReg, indexReg, 2, "IndexExpr: for list, element size = 4 char, so: indexReg *= 4");
+            }
+            backend.emitADD(listReg, listReg, indexReg, "IndexExpr: listPtr += index");
+            backend.emitLW(listReg, listReg, 0, "IndexExpr: result = *listPtr (reuse listPtr)");
+            // listReg,indexReg,lenReg die. listReg => elementReg.
+            if(node.list.getInferredType().equals(SymbolType.STR_TYPE)) {
+                // lenReg => newStrLenReg
+                backend.emitANDI(listReg, listReg, 0x000000FF, "IndexExpr: for string element, wipe higher 3 chars, leave only 1 char");
+                backend.emitLI(lenReg, 1+4, "IndexExpr: result string object size = 4+1 = 5");
+
+                betterBackend.emitAllocPrototype(SymbolType.STR_TYPE, lenReg);
+
+                backend.emitLI(lenReg, 1, "IndexExpr: result string len = 1");
+                backend.emitSW(lenReg, A0, 3*backend.getWordSize(), "IndexExpr: result string.len");
+                backend.emitSW(listReg, A0, 4*backend.getWordSize(), "IndexExpr: result string.data");
+
+                backend.emitMV(listReg, A0, "IndexExpr: move result string to resultReg");
+            }
+            // listReg => resultReg.
+            betterBackend.emitPush(listReg, "IndexExpr: push result!");
+            return null;
+        }
 
-        // FIXME: More, of course.
 
     }