feat(translate): implement EXIT word and fix UNLOOP for early loop exit

lib/Translation/ForthToMLIR/ForthToMLIR.cpp

@@ -588,7 +588,38 @@ LogicalResult ForthParser::parseBody(Value &stack) {
           return emitError("UNLOOP without matching DO");
         }
 
-        (void)loopStack.pop_back_val();
+        // No-op: loop control uses CFG blocks and a memref counter, not the
+        // Forth stack, so there is nothing to discard. We keep the loopStack
+        // intact so that LOOP can still find its matching DO.
+
+        //=== EXIT ===
+      } else if (word == "EXIT") {
+        consume();
+
+        if (!inWordDefinition) {
+          return emitError("EXIT outside word definition");
+        }
+
+        Region *parentRegion = builder.getInsertionBlock()->getParent();
+
+        // Create a block that performs the return.
+        auto *returnBlock = createStackBlock(parentRegion, loc);
+        {
+          OpBuilder::InsertionGuard guard(builder);
+          builder.setInsertionPointToStart(returnBlock);
+          builder.create<func::ReturnOp>(loc, returnBlock->getArgument(0));
+        }
+
+        // Use a dummy cond_br to keep the dead block structurally reachable,
+        // matching the pattern used by LEAVE.
+        auto *deadBlock = createStackBlock(parentRegion, loc);
+        Value cond = builder.create<arith::ConstantOp>(
+            loc, builder.getI1Type(), builder.getBoolAttr(true));
+        builder.create<cf::CondBranchOp>(loc, cond, returnBlock,
+                                         ValueRange{stack}, deadBlock,
+                                         ValueRange{stack});
+        builder.setInsertionPointToStart(deadBlock);
+        stack = deadBlock->getArgument(0);
 
         //=== DO ===
       } else if (word == "DO") {

test/Pipeline/exit.forth

@@ -0,0 +1,6 @@
+\ RUN: %warpforth-translate --forth-to-mlir %s | %warpforth-opt --warpforth-pipeline | %FileCheck %s
+\ CHECK: gpu.binary @warpforth_module
+
+PARAM DATA 4
+: DO-EXIT 1 IF EXIT THEN 42 ;
+DO-EXIT DATA 0 CELLS + !

test/Pipeline/unloop-exit.forth

@@ -0,0 +1,6 @@
+\ RUN: %warpforth-translate --forth-to-mlir %s | %warpforth-opt --warpforth-pipeline | %FileCheck %s
+\ CHECK: gpu.binary @warpforth_module
+
+PARAM DATA 4
+: FIND-FIVE  10 0 DO I 5 = IF UNLOOP EXIT THEN LOOP 0 ;
+FIND-FIVE DATA 0 CELLS + !

test/Translation/Forth/exit-outside-word-error.forth

@@ -0,0 +1,3 @@
+\ RUN: %not %warpforth-translate --forth-to-mlir %s 2>&1 | %FileCheck %s
+\ CHECK: EXIT outside word definition
+EXIT

test/Translation/Forth/exit.forth

@@ -0,0 +1,13 @@
+\ RUN: %warpforth-translate --forth-to-mlir %s | %FileCheck %s
+
+\ CHECK: func.func private @EARLY_EXIT(%[[A:.*]]: !forth.stack) -> !forth.stack
+\ CHECK:   cf.cond_br %{{.*}}, ^[[THEN:bb.*]](%{{.*}}), ^[[JOIN:bb.*]](%{{.*}})
+\ CHECK: ^[[THEN]](%[[T:.*]]: !forth.stack):
+\ CHECK:   cf.cond_br %true, ^[[RET:bb.*]](%[[T]]{{.*}}), ^[[DEAD:bb.*]](%[[T]]
+\ CHECK: ^[[JOIN]](%{{.*}}: !forth.stack):
+\ CHECK:   return %{{.*}} : !forth.stack
+\ CHECK: ^[[RET]](%[[R:.*]]: !forth.stack):
+\ CHECK:   return %[[R]] : !forth.stack
+
+: EARLY-EXIT 1 IF EXIT THEN 42 ;
+EARLY-EXIT

test/Translation/Forth/unloop-exit.forth

@@ -0,0 +1,21 @@
+\ RUN: %warpforth-translate --forth-to-mlir %s | %FileCheck %s
+
+\ Verify the UNLOOP EXIT idiom: early return from a DO LOOP inside a word.
+
+\ CHECK: func.func private @FIND_FIVE(%{{.*}}: !forth.stack) -> !forth.stack
+\ CHECK: memref.alloca
+\ CHECK: cf.br ^bb[[#CHECK:]]
+\ CHECK: ^bb[[#CHECK]](%{{.*}}: !forth.stack):
+\ CHECK: cf.cond_br %{{.*}}, ^bb[[#BODY:]](%{{.*}}), ^bb[[#EXIT:]](%{{.*}})
+\ CHECK: ^bb[[#BODY]](%{{.*}}: !forth.stack):
+\ CHECK: forth.eq
+\ CHECK: cf.cond_br %{{.*}}, ^bb[[#THEN:]](%{{.*}}), ^bb[[#ENDIF:]](%{{.*}})
+\ CHECK: ^bb[[#EXIT]](%{{.*}}: !forth.stack):
+\ CHECK: return
+\ CHECK: ^bb[[#THEN]](%[[T:.*]]: !forth.stack):
+\ CHECK: cf.cond_br %true, ^bb[[#RET:]](%[[T]]{{.*}})
+\ CHECK: ^bb[[#RET]](%[[R:.*]]: !forth.stack):
+\ CHECK: return %[[R]] : !forth.stack
+
+: FIND-FIVE  10 0 DO I 5 = IF UNLOOP EXIT THEN LOOP 0 ;
+FIND-FIVE