Auto merge of #101152 - Dylan-DPC:rollup-v4iw8ux, r=Dylan-DPC

Rollup of 8 pull requests

Successful merges:

 - #98304 (Add MaybeUninit memset test)
 - #98801 (Add a `File::create_new` constructor)
 - #99821 (Remove separate indexing of early-bound regions)
 - #100239 (remove an ineffective check in const_prop)
 - #100337 (Stabilize `std::io::read_to_string`)
 - #100819 (Make use of `[wrapping_]byte_{add,sub}`)
 - #100934 (Remove a panicking branch from `fmt::builders::PadAdapter`)
 - #101000 (Separate CountIsStar from CountIsParam in rustc_parse_format.)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 53 insertions, 32 deletions

diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs
index 5c9f4f57243..53f33a7a0ba 100644
--- a/compiler/rustc_mir_transform/src/const_prop.rs
+++ b/compiler/rustc_mir_transform/src/const_prop.rs
@@ -243,24 +243,6 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
         throw_machine_stop_str!("pointer arithmetic or comparisons aren't supported in ConstProp")
     }
 
-    fn access_local<'a>(
-        frame: &'a Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>,
-        local: Local,
-    ) -> InterpResult<'tcx, &'a interpret::Operand<Self::Provenance>> {
-        let l = &frame.locals[local];
-
-        if matches!(
-            l.value,
-            LocalValue::Live(interpret::Operand::Immediate(interpret::Immediate::Uninit))
-        ) {
-            // For us "uninit" means "we don't know its value, might be initiailized or not".
-            // So stop here.
-            throw_machine_stop_str!("tried to access alocal with unknown value ")
-        }
-
-        l.access()
-    }
-
     fn access_local_mut<'a>(
         ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
         frame: usize,
@@ -431,7 +413,13 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
 
     fn get_const(&self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {
         let op = match self.ecx.eval_place_to_op(place, None) {
-            Ok(op) => op,
+            Ok(op) => {
+                if matches!(*op, interpret::Operand::Immediate(Immediate::Uninit)) {
+                    // Make sure nobody accidentally uses this value.
+                    return None;
+                }
+                op
+            }
             Err(e) => {
                 trace!("get_const failed: {}", e);
                 return None;
@@ -643,6 +631,14 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         if rvalue.needs_subst() {
             return None;
         }
+        if !rvalue
+            .ty(&self.ecx.frame().body.local_decls, *self.ecx.tcx)
+            .is_sized(self.ecx.tcx, self.param_env)
+        {
+            // the interpreter doesn't support unsized locals (only unsized arguments),
+            // but rustc does (in a kinda broken way), so we have to skip them here
+            return None;
+        }
 
         if self.tcx.sess.mir_opt_level() >= 4 {
             self.eval_rvalue_with_identities(rvalue, place)
@@ -660,18 +656,20 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         self.use_ecx(|this| match rvalue {
             Rvalue::BinaryOp(op, box (left, right))
             | Rvalue::CheckedBinaryOp(op, box (left, right)) => {
-                let l = this.ecx.eval_operand(left, None);
-                let r = this.ecx.eval_operand(right, None);
+                let l = this.ecx.eval_operand(left, None).and_then(|x| this.ecx.read_immediate(&x));
+                let r =
+                    this.ecx.eval_operand(right, None).and_then(|x| this.ecx.read_immediate(&x));
 
                 let const_arg = match (l, r) {
-                    (Ok(ref x), Err(_)) | (Err(_), Ok(ref x)) => this.ecx.read_immediate(x)?,
-                    (Err(e), Err(_)) => return Err(e),
-                    (Ok(_), Ok(_)) => return this.ecx.eval_rvalue_into_place(rvalue, place),
+                    (Ok(x), Err(_)) | (Err(_), Ok(x)) => x, // exactly one side is known
+                    (Err(e), Err(_)) => return Err(e),      // neither side is known
+                    (Ok(_), Ok(_)) => return this.ecx.eval_rvalue_into_place(rvalue, place), // both sides are known
                 };
 
                 if !matches!(const_arg.layout.abi, abi::Abi::Scalar(..)) {
                     // We cannot handle Scalar Pair stuff.
-                    return this.ecx.eval_rvalue_into_place(rvalue, place);
+                    // No point in calling `eval_rvalue_into_place`, since only one side is known
+                    throw_machine_stop_str!("cannot optimize this")
                 }
 
                 let arg_value = const_arg.to_scalar().to_bits(const_arg.layout.size)?;
@@ -696,7 +694,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                             this.ecx.write_immediate(*const_arg, &dest)
                         }
                     }
-                    _ => this.ecx.eval_rvalue_into_place(rvalue, place),
+                    _ => throw_machine_stop_str!("cannot optimize this"),
                 }
             }
             _ => this.ecx.eval_rvalue_into_place(rvalue, place),
@@ -1073,7 +1071,11 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
                 if let Some(ref value) = self.eval_operand(&cond) {
                     trace!("assertion on {:?} should be {:?}", value, expected);
                     let expected = Scalar::from_bool(*expected);
-                    let value_const = self.ecx.read_scalar(&value).unwrap();
+                    let Ok(value_const) = self.ecx.read_scalar(&value) else {
+                        // FIXME should be used use_ecx rather than a local match... but we have
+                        // quite a few of these read_scalar/read_immediate that need fixing.
+                        return
+                    };
                     if expected != value_const {
                         // Poison all places this operand references so that further code
                         // doesn't use the invalid value
diff --git a/compiler/rustc_mir_transform/src/const_prop_lint.rs b/compiler/rustc_mir_transform/src/const_prop_lint.rs
index 74b146833d0..082d6c9f07e 100644
--- a/compiler/rustc_mir_transform/src/const_prop_lint.rs
+++ b/compiler/rustc_mir_transform/src/const_prop_lint.rs
@@ -6,6 +6,7 @@ use crate::const_prop::ConstPropMachine;
 use crate::const_prop::ConstPropMode;
 use crate::MirLint;
 use rustc_const_eval::const_eval::ConstEvalErr;
+use rustc_const_eval::interpret::Immediate;
 use rustc_const_eval::interpret::{
     self, InterpCx, InterpResult, LocalState, LocalValue, MemoryKind, OpTy, Scalar, StackPopCleanup,
 };
@@ -229,7 +230,13 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
 
     fn get_const(&self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {
         let op = match self.ecx.eval_place_to_op(place, None) {
-            Ok(op) => op,
+            Ok(op) => {
+                if matches!(*op, interpret::Operand::Immediate(Immediate::Uninit)) {
+                    // Make sure nobody accidentally uses this value.
+                    return None;
+                }
+                op
+            }
             Err(e) => {
                 trace!("get_const failed: {}", e);
                 return None;
@@ -515,6 +522,14 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         if rvalue.needs_subst() {
             return None;
         }
+        if !rvalue
+            .ty(&self.ecx.frame().body.local_decls, *self.ecx.tcx)
+            .is_sized(self.ecx.tcx, self.param_env)
+        {
+            // the interpreter doesn't support unsized locals (only unsized arguments),
+            // but rustc does (in a kinda broken way), so we have to skip them here
+            return None;
+        }
 
         self.use_ecx(source_info, |this| this.ecx.eval_rvalue_into_place(rvalue, place))
     }
@@ -624,7 +639,11 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
                 if let Some(ref value) = self.eval_operand(&cond, source_info) {
                     trace!("assertion on {:?} should be {:?}", value, expected);
                     let expected = Scalar::from_bool(*expected);
-                    let value_const = self.ecx.read_scalar(&value).unwrap();
+                    let Ok(value_const) = self.ecx.read_scalar(&value) else {
+                        // FIXME should be used use_ecx rather than a local match... but we have
+                        // quite a few of these read_scalar/read_immediate that need fixing.
+                        return
+                    };
                     if expected != value_const {
                         enum DbgVal<T> {
                             Val(T),
@@ -641,9 +660,9 @@ impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
                         let mut eval_to_int = |op| {
                             // This can be `None` if the lhs wasn't const propagated and we just
                             // triggered the assert on the value of the rhs.
-                            self.eval_operand(op, source_info).map_or(DbgVal::Underscore, |op| {
-                                DbgVal::Val(self.ecx.read_immediate(&op).unwrap().to_const_int())
-                            })
+                            self.eval_operand(op, source_info)
+                                .and_then(|op| self.ecx.read_immediate(&op).ok())
+                                .map_or(DbgVal::Underscore, |op| DbgVal::Val(op.to_const_int()))
                         };
                         let msg = match msg {
                             AssertKind::DivisionByZero(op) => {