https://gcc.gnu.org/g:c6781f5558bdb4f241a3597c528ed7020a5cfce7
commit r16-4014-gc6781f5558bdb4f241a3597c528ed7020a5cfce7 Author: Andrew Pinski <[email protected]> Date: Fri Sep 19 12:23:57 2025 -0700 fab: Remove forced label check from optimize_unreachable Since optimize_unreachable does not directly remove the bb, we can still remove the condition that goes to a block containing a forced label. This is a small cleanup from the original patch which added optimize_unreachable. The review of the original patch missed that the bb was not being removed by the pass but later on by cleanupcfg; https://gcc.gnu.org/pipermail/gcc-patches/2012-July/343239.html. Which is why this is allowed to be done. I added another testcase to check that the `if` is removed too. Bootstrapped and tested on x86_64-linux-gnu. gcc/ChangeLog: * tree-ssa-ccp.cc (optimize_unreachable): Don't check for forced labels. gcc/testsuite/ChangeLog: * gcc.dg/builtin-unreachable-7.c: New test. Signed-off-by: Andrew Pinski <[email protected]> Diff: --- gcc/testsuite/gcc.dg/builtin-unreachable-7.c | 24 +++++++++++++++++++++++ gcc/tree-ssa-ccp.cc | 29 ++++++---------------------- 2 files changed, 30 insertions(+), 23 deletions(-) diff --git a/gcc/testsuite/gcc.dg/builtin-unreachable-7.c b/gcc/testsuite/gcc.dg/builtin-unreachable-7.c new file mode 100644 index 000000000000..a6c078fef285 --- /dev/null +++ b/gcc/testsuite/gcc.dg/builtin-unreachable-7.c @@ -0,0 +1,24 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-fab1 -fno-tree-dominator-opts -fno-tree-vrp" } */ +/* { dg-require-effective-target label_values } */ + +void foo (int b, int c) +{ + __label__ lab; + __label__ lab2; + static void *x[2] = {&&lab, &&lab2}; + if (b == c) + { +lab: + __builtin_unreachable (); + } +lab2: + goto *x[c!=0]; +} + +/* Fab should still able to remove the conditional but leave the bb there. */ + +/* { dg-final { scan-tree-dump-times "lab:" 1 "fab1" } } */ +/* { dg-final { scan-tree-dump-times "__builtin_unreachable" 1 "fab1" } } */ +/* { dg-final { scan-tree-dump-not "if " "fab1" } } */ + diff --git a/gcc/tree-ssa-ccp.cc b/gcc/tree-ssa-ccp.cc index f16b37f193e2..546cafbf7c69 100644 --- a/gcc/tree-ssa-ccp.cc +++ b/gcc/tree-ssa-ccp.cc @@ -3260,29 +3260,12 @@ optimize_unreachable (gimple_stmt_iterator i) if (flag_sanitize & SANITIZE_UNREACHABLE) return false; - - for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) - { - stmt = gsi_stmt (gsi); - - if (is_gimple_debug (stmt)) - continue; - - if (glabel *label_stmt = dyn_cast <glabel *> (stmt)) - { - /* Verify we do not need to preserve the label. */ - if (FORCED_LABEL (gimple_label_label (label_stmt))) - return false; - - continue; - } - - /* Only handle the case that __builtin_unreachable is the first statement - in the block. We rely on DCE to remove stmts without side-effects - before __builtin_unreachable. */ - if (gsi_stmt (gsi) != gsi_stmt (i)) - return false; - } + gsi = gsi_start_nondebug_after_labels_bb (bb); + /* Only handle the case that __builtin_unreachable is the first + statement in the block. We rely on DCE to remove stmts + without side-effects before __builtin_unreachable. */ + if (*gsi != *i) + return false; ret = false; FOR_EACH_EDGE (e, ei, bb->preds)
