Merge from rustc

Author: The rustc-dev-guide Cronjob Bot

src/concurrency/data_race.rs

@@ -717,7 +717,7 @@ pub trait EvalContextExt<'tcx>: MiriInterpCxExt<'tcx> {
         // The program didn't actually do a read, so suppress the memory access hooks.
         // This is also a very special exception where we just ignore an error -- if this read
         // was UB e.g. because the memory is uninitialized, we don't want to know!
-        let old_val = this.run_for_validation(|this| this.read_scalar(dest)).discard_err();
+        let old_val = this.run_for_validation_mut(|this| this.read_scalar(dest)).discard_err();
         this.allow_data_races_mut(move |this| this.write_scalar(val, dest))?;
         this.validate_atomic_store(dest, atomic)?;
         this.buffered_atomic_write(val, dest, atomic, old_val)

src/intrinsics/mod.rs

@@ -411,9 +411,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 };
                 let res = this.binary_op(op, &a, &b)?;
                 // `binary_op` already called `generate_nan` if needed.
-                // Apply a relative error of 16ULP to simulate non-deterministic precision loss
+                // Apply a relative error of 4ULP to simulate non-deterministic precision loss
                 // due to optimizations.
-                let res = apply_random_float_error_to_imm(this, res, 4 /* log2(16) */)?;
+                let res = apply_random_float_error_to_imm(this, res, 2 /* log2(4) */)?;
                 this.write_immediate(*res, dest)?;
             }
 
@@ -464,9 +464,9 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 if !float_finite(&res)? {
                     throw_ub_format!("`{intrinsic_name}` intrinsic produced non-finite value as result");
                 }
-                // Apply a relative error of 16ULP to simulate non-deterministic precision loss
+                // Apply a relative error of 4ULP to simulate non-deterministic precision loss
                 // due to optimizations.
-                let res = apply_random_float_error_to_imm(this, res, 4 /* log2(16) */)?;
+                let res = apply_random_float_error_to_imm(this, res, 2 /* log2(4) */)?;
                 this.write_immediate(*res, dest)?;
             }