Fix ICE with continue/break/return in while condition

Fixes #3977

The predicate expression must be evaluated before type checking
to ensure side effects occur even when the predicate has never type.
This prevents skipping function calls, panics, or other side effects
in diverging predicates.

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): Always
	evaluate predicate expression before checking for never type
	to preserve side effects in while loop conditions.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3977.rs: New test.

Signed-off-by: Harishankar <harishankarpp7@gmail.com>

Author: Harishankar14

gcc/rust/backend/rust-compile-expr.cc

@@ -803,7 +803,18 @@ CompileExpr::visit (HIR::WhileLoopExpr &expr)
   ctx->add_statement (loop_begin_label_decl);
   ctx->push_loop_begin_label (loop_begin_label);
 
-  tree condition = CompileExpr::Compile (expr.get_predicate_expr (), ctx);
+  HIR::Expr &predicate = expr.get_predicate_expr ();
+  TyTy::BaseType *predicate_type = nullptr;
+  bool ok
+    = ctx->get_tyctx ()->lookup_type (predicate.get_mappings ().get_hirid (),
+				      &predicate_type);
+  rust_assert (ok && predicate_type != nullptr);
+  tree condition = CompileExpr::Compile (predicate, ctx);
+  if (predicate_type->get_kind () == TyTy::TypeKind::NEVER)
+    {
+      ctx->add_statement (condition);
+      condition = boolean_true_node;
+    }
   tree exit_condition = fold_build1_loc (expr.get_locus (), TRUTH_NOT_EXPR,
 					 boolean_type_node, condition);
   tree exit_expr = Backend::exit_expression (exit_condition, expr.get_locus ());

gcc/rust/typecheck/rust-hir-type-check-expr.cc

@@ -1543,25 +1543,11 @@ TypeCheckExpr::visit (HIR::WhileLoopExpr &expr)
   context->push_new_while_loop_context (expr.get_mappings ().get_hirid ());
   TyTy::BaseType *predicate_type
     = TypeCheckExpr::Resolve (expr.get_predicate_expr ());
-  if (predicate_type->get_kind () == TyTy::TypeKind::ERROR)
-    {
-      infered = TyTy::TupleType::get_unit_type ();
-      context->pop_loop_context ();
-      return;
-    }
-  if (predicate_type->get_kind () == TyTy::TypeKind::NEVER)
-    {
-      rust_error_at (expr.get_predicate_expr ().get_locus (),
-		     "expected boolean expression in %<while%> condition");
-      infered = TyTy::TupleType::get_unit_type ();
-      context->pop_loop_context ();
-      return;
-    }
-  if (predicate_type->get_kind () != TyTy::TypeKind::BOOL)
+  if (predicate_type->get_kind () != TyTy::TypeKind::BOOL
+      && predicate_type->get_kind () != TyTy::TypeKind::NEVER)
     {
       rust_error_at (expr.get_predicate_expr ().get_locus (),
 		     "expected boolean expression in %<while%> condition");
-      infered = TyTy::TupleType::get_unit_type ();
       context->pop_loop_context ();
       return;
     }
@@ -1571,13 +1557,6 @@ TypeCheckExpr::visit (HIR::WhileLoopExpr &expr)
       rust_error_at (expr.get_loop_block ().get_locus (),
 		     "expected %<()%> got %s",
 		     block_expr->as_string ().c_str ());
-      infered = TyTy::TupleType::get_unit_type ();
-      context->pop_loop_context ();
-      return;
-    }
-  if (block_expr->get_kind () == TyTy::TypeKind::ERROR)
-    {
-      infered = TyTy::TupleType::get_unit_type ();
       context->pop_loop_context ();
       return;
     }
@@ -1630,7 +1609,6 @@ TypeCheckExpr::visit (HIR::ContinueExpr &expr)
 		     "%<continue%> outside of a loop");
       return;
     }
-
   infered = new TyTy::NeverType (expr.get_mappings ().get_hirid ());
 }
 

gcc/testsuite/rust/compile/issue-3977.rs

@@ -1,72 +1,65 @@
-// Test for issue #3977: ICE in fold_convert_loc with diverging expressions in while conditions
-// { dg-excess-errors "expected boolean expression" }
+// Test for issue #3977 - ICE with continue/break/return in while condition
+
+fn diverge() -> ! {
+    loop {}
+}
 
 fn test_continue() {
     loop {
-        while continue {} // { dg-error "expected boolean expression in 'while' condition" }
+        while continue {}
     }
 }
 
-fn test_break() {
+fn test_break() {      
     loop {
-        while break {} // { dg-error "expected boolean expression in 'while' condition" }
+        while break {}
     }
 }
 
 fn test_return() {
-    while return {} // { dg-error "expected boolean expression in 'while' condition" }
-}
-
-fn test_return_with_value() {
-    while return 42 {} // { dg-error "expected boolean expression in 'while' condition" }
-}
-
-fn test_infinite_loop() {
-    while loop {} {} // { dg-error "expected boolean expression in 'while' condition" }
-}
-
-fn test_nested_continue() {
     loop {
-        loop {
-            while continue {} // { dg-error "expected boolean expression in 'while' condition" }
-        }
+        while return {}
     }
 }
 
 fn test_labeled_break() {
     'outer: loop {
-        while break 'outer {} // { dg-error "expected boolean expression in 'while' condition" }
+        loop {
+            while break 'outer {}
+        }
     }
 }
 
 fn test_labeled_continue() {
     'outer: loop {
-        while continue 'outer {} // { dg-error "expected boolean expression in 'while' condition" }
+        loop {
+            while continue 'outer {}
+        }
     }
 }
 
-// Valid cases that should NOT error
-fn test_valid_boolean() {
-    while true {}
-    while false {}
-}
-
-fn test_valid_expression() {
-    let x = 5;
-    while x > 0 {}
+fn test_complex_if_else() {
+    loop {
+        while if true { continue } else { break } {}
+    }
 }
 
-fn test_valid_function_call() -> bool {
-    fn condition() -> bool { true }
-    while condition() {}
-    true
+fn foo() {
+    while diverge() {
+        break
+    }
+    let _x = 5;
 }
 
 fn main() {
-    test_valid_boolean();
-    test_valid_expression();
-    test_valid_function_call();
-    
-    // The error cases would cause compilation to fail
-    // so they're tested separately
+    // Just reference them so they're "used"
+    if false {
+        test_continue();
+        test_break();
+        test_return();
+        test_labeled_break();
+        test_labeled_continue();
+        test_complex_if_else();
+        foo();
+    }
 }