[Bug target/124137] [16 Regression] build doesn't finish after 4h+

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124137

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
A testcase could be reduced with

diff --git a/gcc/config/i386/i386-features.cc
b/gcc/config/i386/i386-features.cc
index 8e277843f23..df04decda7f 100644
--- a/gcc/config/i386/i386-features.cc
+++ b/gcc/config/i386/i386-features.cc
@@ -4042,7 +4042,9 @@ ix86_emit_tls_call (rtx tls_set, x86_cse_kind kind,
basic_block bb,
              /* Place the call before all FLAGS_REG setting BBs since
                 we can't place a call before nor after a conditional
                 jump.  */
-             bb = ix86_get_dominator_for_reg (FLAGS_REG, bb);
+             auto bb1 = ix86_get_dominator_for_reg (FLAGS_REG, bb);
+             gcc_assert (bb1 != bb);
+             bb = bb1;

              /* Start over again.  */
              repeat = true;