compiler: Require mir_opt_level > 1 for SingleUseConsts

To make `tests/debuginfo/basic-stepping.rs` pass.

Note that we must keep `SingleUseConsts` enabled for
`tests/ui-fulldeps/rustc_public/check_allocation.rs` since its
`fn collect_consts()` assumes that:

    VarDebugInfo {
        name: "_false",
        [...]
        value: Place(
            _5,
        ),
    }

is transformed into which is what `SingleUseConsts` does:

    VarDebugInfo {
        name: "_false",
        [...]
        value: Const(
            [...]
        ),
    }

Author: Enselic

compiler/rustc_mir_transform/src/single_use_consts.rs

@@ -23,7 +23,7 @@ pub(super) struct SingleUseConsts;
 
 impl<'tcx> crate::MirPass<'tcx> for SingleUseConsts {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() > 0
+        sess.mir_opt_level() > 1
     }
 
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {

tests/debuginfo/basic-stepping.rs

@@ -10,23 +10,19 @@
 // Debugger tests need debuginfo
 //@ compile-flags: -g
 
-// FIXME(#128945): SingleUseConsts shouldn't need to be disabled.
-//@ revisions: default-mir-passes no-SingleUseConsts-mir-pass
-//@ [no-SingleUseConsts-mir-pass] compile-flags: -Zmir-enable-passes=-SingleUseConsts
-
 //@ gdb-command: run
 // FIXME(#97083): Should we be able to break on initialization of zero-sized types?
 // FIXME(#97083): Right now the first breakable line is:
 //@ gdb-check:   let mut c = 27;
 //@ gdb-command: next
 //@ gdb-check:   let d = c = 99;
 //@ gdb-command: next
-//@ [no-SingleUseConsts-mir-pass] gdb-check:   let e = "hi bob";
-//@ [no-SingleUseConsts-mir-pass] gdb-command: next
-//@ [no-SingleUseConsts-mir-pass] gdb-check:   let f = b"hi bob";
-//@ [no-SingleUseConsts-mir-pass] gdb-command: next
-//@ [no-SingleUseConsts-mir-pass] gdb-check:   let g = b'9';
-//@ [no-SingleUseConsts-mir-pass] gdb-command: next
+//@ gdb-check:   let e = "hi bob";
+//@ gdb-command: next
+//@ gdb-check:   let f = b"hi bob";
+//@ gdb-command: next
+//@ gdb-check:   let g = b'9';
+//@ gdb-command: next
 //@ gdb-check:   let h = ["whatever"; 8];
 //@ gdb-command: next
 //@ gdb-check:   let i = [1,2,3,4];

tests/debuginfo/macro-stepping.rs

@@ -15,9 +15,6 @@
 extern crate macro_stepping; // exports new_scope!()
 
 //@ compile-flags: -g
-// FIXME(#128945): SingleUseConsts shouldn't need to be disabled.
-//@ revisions: default-mir-passes no-SingleUseConsts-mir-pass
-//@ [no-SingleUseConsts-mir-pass] compile-flags: -Zmir-enable-passes=-SingleUseConsts
 
 // === GDB TESTS ===================================================================================
 
@@ -50,7 +47,7 @@ extern crate macro_stepping; // exports new_scope!()
 //@ gdb-check:[...]#inc-loc2[...]
 //@ gdb-command:next
 //@ gdb-command:frame
-//@ [no-SingleUseConsts-mir-pass] gdb-check:[...]#inc-loc3[...]
+//@ gdb-check:[...]#inc-loc3[...]
 
 // === LLDB TESTS ==================================================================================
 

tests/ui-fulldeps/rustc_public/check_allocation.rs

@@ -209,6 +209,7 @@ fn main() {
     generate_input(&path).unwrap();
     let args = &[
         "rustc".to_string(),
+        "-Zmir-enable-passes=+SingleUseConsts".to_string(), // Needed for `fn collect_consts()`
         "--edition=2021".to_string(),
         "--crate-name".to_string(),
         CRATE_NAME.to_string(),