https://gcc.gnu.org/g:d994d2bd3596f520c7fbe4ab133d6e02607cd9bd
commit r17-1216-gd994d2bd3596f520c7fbe4ab133d6e02607cd9bd Author: Marc Poulhiès <[email protected]> Date: Thu Apr 9 12:28:23 2026 +0200 ada: Avoid definition of unused label for LOOP_STMT The gimplification of LOOP_STMT has a systematic end label definition, that may be unused. For example, an endless loop maybe gimplified to: <D.5765>: # USE = anything # CLB = anything totoD.5747 (); goto <D.5765>; <D.5749>: Later, the gimple_seq_may_fallthru() will decide that this block can fallthru as the last statement is a single label that may be jumped to from somewhere else. Only defining this label if we also emit jumps to it helps the compiler correctly decide if the block can fallthru or not. In particular, if a function, with a local object needing finalization and the No_Return aspect, is an endless loop then the spurious warning that the function is still returning is not emitted anymore. gcc/ada/ChangeLog: * gcc-interface/trans.cc (gnat_to_gnu) <N_Exit_Statement>: Mark the label tree as used. (gnat_gimplify_stmt) <LOOP_STMT>: Do not emit end label definition in unused. Diff: --- gcc/ada/gcc-interface/trans.cc | 32 ++++++++++++++++++++------------ 1 file changed, 20 insertions(+), 12 deletions(-) diff --git a/gcc/ada/gcc-interface/trans.cc b/gcc/ada/gcc-interface/trans.cc index 5140ed8bbfda..7df32d67ea9a 100644 --- a/gcc/ada/gcc-interface/trans.cc +++ b/gcc/ada/gcc-interface/trans.cc @@ -7993,13 +7993,17 @@ gnat_to_gnu (Node_Id gnat_node) break; case N_Exit_Statement: - gnu_result - = build2 (EXIT_STMT, void_type_node, - (Present (Condition (gnat_node)) - ? gnat_to_gnu (Condition (gnat_node)) : NULL_TREE), - (Present (Name (gnat_node)) - ? get_gnu_tree (Entity (Name (gnat_node))) - : LOOP_STMT_LABEL (gnu_loop_stack->last ()->stmt))); + { + tree end_loop_label = Present (Name (gnat_node)) + ? get_gnu_tree (Entity (Name (gnat_node))) + : LOOP_STMT_LABEL (gnu_loop_stack->last ()->stmt); + gnu_result + = build2 (EXIT_STMT, void_type_node, + (Present (Condition (gnat_node)) + ? gnat_to_gnu (Condition (gnat_node)) : NULL_TREE), + end_loop_label); + TREE_USED (end_loop_label) = 1; + } break; case N_Simple_Return_Statement: @@ -9532,6 +9536,8 @@ gnat_gimplify_stmt (tree *stmt_p) gnu_cond = build3 (COND_EXPR, void_type_node, gnu_cond, NULL_TREE, build1 (GOTO_EXPR, void_type_node, gnu_end_label)); + + TREE_USED (gnu_end_label) = 1; } /* Set to emit the statements of the loop. */ @@ -9541,8 +9547,9 @@ gnat_gimplify_stmt (tree *stmt_p) end label if there's a top condition, then the update if it's at the top, then the body of the loop, then a conditional jump to the end label if there's a bottom condition, then the update if - it's at the bottom, and finally a jump to the start label and the - definition of the end label. */ + it's at the bottom, and finally a jump to the start label and if + there's a top or bottom condition, the definition of the end + label. */ append_to_statement_list (build1 (LABEL_EXPR, void_type_node, gnu_start_label), stmt_p); @@ -9565,9 +9572,10 @@ gnat_gimplify_stmt (tree *stmt_p) SET_EXPR_LOCATION (t, DECL_SOURCE_LOCATION (gnu_end_label)); append_to_statement_list (t, stmt_p); - append_to_statement_list (build1 (LABEL_EXPR, void_type_node, - gnu_end_label), - stmt_p); + if (TREE_USED (gnu_end_label)) + append_to_statement_list (build1 (LABEL_EXPR, void_type_node, + gnu_end_label), + stmt_p); return GS_OK; }
