Auto merge of rust-lang#109521 - tmiasko:const-prop-validation, r=wesleywiser

Don't validate constants in const propagation

Validation is neither necessary nor desirable.

The constant validation is already omitted at mir-opt-level >= 3, so there there are not changes in MIR test output (the propagation of invalid constants is covered by an existing test in tests/mir-opt/const_prop/invalid_constant.rs).

Author: bors

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -38,16 +38,14 @@ macro_rules! throw_validation_failure {
             msg.push_str(", but expected ");
             write!(&mut msg, $($expected_fmt)*).unwrap();
         )?
-        let path = rustc_middle::ty::print::with_no_trimmed_paths!({
-            let where_ = &$where;
-            if !where_.is_empty() {
-                let mut path = String::new();
-                write_path(&mut path, where_);
-                Some(path)
-            } else {
-                None
-            }
-        });
+        let where_ = &$where;
+        let path = if !where_.is_empty() {
+            let mut path = String::new();
+            write_path(&mut path, where_);
+            Some(path)
+        } else {
+            None
+        };
         throw_ub!(ValidationFailure { path, msg })
     }};
 }

compiler/rustc_mir_transform/src/const_prop.rs

@@ -21,9 +21,9 @@ use rustc_target::spec::abi::Abi as CallAbi;
 
 use crate::MirPass;
 use rustc_const_eval::interpret::{
-    self, compile_time_machine, AllocId, ConstAllocation, ConstValue, CtfeValidationMode, Frame,
-    ImmTy, Immediate, InterpCx, InterpResult, LocalValue, MemoryKind, OpTy, PlaceTy, Pointer,
-    Scalar, StackPopCleanup,
+    self, compile_time_machine, AllocId, ConstAllocation, ConstValue, Frame, ImmTy, Immediate,
+    InterpCx, InterpResult, LocalValue, MemoryKind, OpTy, PlaceTy, Pointer, Scalar,
+    StackPopCleanup,
 };
 
 /// The maximum number of bytes that we'll allocate space for a local or the return value.
@@ -464,16 +464,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
 
                 return None;
             }
-            // Do not try creating references, nor any types with potentially-complex
-            // invariants. This avoids an issue where checking validity would do a
-            // bunch of work generating a nice message about the invariant violation,
-            // only to not show it to anyone (since this isn't the lint).
-            Rvalue::Cast(CastKind::Transmute, op, dst_ty) if !dst_ty.is_primitive() => {
-                trace!("skipping Transmute of {:?} to {:?}", op, dst_ty);
-
-                return None;
-            }
-
             // There's no other checking to do at this time.
             Rvalue::Aggregate(..)
             | Rvalue::Use(..)
@@ -591,18 +581,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         }
 
         trace!("attempting to replace {:?} with {:?}", rval, value);
-        if let Err(e) = self.ecx.const_validate_operand(
-            value,
-            vec![],
-            // FIXME: is ref tracking too expensive?
-            // FIXME: what is the point of ref tracking if we do not even check the tracked refs?
-            &mut interpret::RefTracking::empty(),
-            CtfeValidationMode::Regular,
-        ) {
-            trace!("validation error, attempt failed: {:?}", e);
-            return;
-        }
-
         // FIXME> figure out what to do when read_immediate_raw fails
         let imm = self.ecx.read_immediate_raw(value).ok();
 

tests/mir-opt/const_prop/transmute.from_char.ConstProp.diff renamed to tests/mir-opt/const_prop/transmute.from_char.ConstProp.32bit.diff

@@ -0,0 +1,15 @@
+- // MIR for `from_char` before ConstProp
++ // MIR for `from_char` after ConstProp
+  
+  fn from_char() -> i32 {
+      let mut _0: i32;                     // return place in scope 0 at $DIR/transmute.rs:+0:23: +0:26
+      scope 1 {
+      }
+  
+      bb0: {
+-         _0 = const 'R' as i32 (Transmute); // scope 1 at $DIR/transmute.rs:+1:14: +1:28
++         _0 = const 82_i32;               // scope 1 at $DIR/transmute.rs:+1:14: +1:28
+          return;                          // scope 0 at $DIR/transmute.rs:+2:2: +2:2
+      }
+  }
+  

tests/mir-opt/const_prop/transmute.from_char.ConstProp.64bit.diff

@@ -7,7 +7,8 @@
       }
 
       bb0: {
-          _0 = const -1_i8 as bool (Transmute); // scope 1 at $DIR/transmute.rs:+1:14: +1:30
+-         _0 = const -1_i8 as bool (Transmute); // scope 1 at $DIR/transmute.rs:+1:14: +1:30
++         _0 = const {transmute(0xff): bool}; // scope 1 at $DIR/transmute.rs:+1:14: +1:30
           return;                          // scope 0 at $DIR/transmute.rs:+2:2: +2:2
       }
   }

tests/mir-opt/const_prop/transmute.invalid_bool.ConstProp.diff renamed to tests/mir-opt/const_prop/transmute.invalid_bool.ConstProp.32bit.diff

@@ -0,0 +1,15 @@
+- // MIR for `invalid_bool` before ConstProp
++ // MIR for `invalid_bool` after ConstProp
+  
+  fn invalid_bool() -> bool {
+      let mut _0: bool;                    // return place in scope 0 at $DIR/transmute.rs:+0:33: +0:37
+      scope 1 {
+      }
+  
+      bb0: {
+-         _0 = const -1_i8 as bool (Transmute); // scope 1 at $DIR/transmute.rs:+1:14: +1:30
++         _0 = const {transmute(0xff): bool}; // scope 1 at $DIR/transmute.rs:+1:14: +1:30
+          return;                          // scope 0 at $DIR/transmute.rs:+2:2: +2:2
+      }
+  }
+  

tests/mir-opt/const_prop/transmute.invalid_bool.ConstProp.64bit.diff

@@ -7,7 +7,8 @@
       }
 
       bb0: {
-          _0 = const _ as char (Transmute); // scope 1 at $DIR/transmute.rs:+1:14: +1:33
+-         _0 = const _ as char (Transmute); // scope 1 at $DIR/transmute.rs:+1:14: +1:33
++         _0 = const {transmute(0x7fffffff): char}; // scope 1 at $DIR/transmute.rs:+1:14: +1:33
           return;                          // scope 0 at $DIR/transmute.rs:+2:2: +2:2
       }
   }

tests/mir-opt/const_prop/transmute.invalid_char.ConstProp.diff renamed to tests/mir-opt/const_prop/transmute.invalid_char.ConstProp.32bit.diff

@@ -0,0 +1,15 @@
+- // MIR for `invalid_char` before ConstProp
++ // MIR for `invalid_char` after ConstProp
+  
+  fn invalid_char() -> char {
+      let mut _0: char;                    // return place in scope 0 at $DIR/transmute.rs:+0:33: +0:37
+      scope 1 {
+      }
+  
+      bb0: {
+-         _0 = const _ as char (Transmute); // scope 1 at $DIR/transmute.rs:+1:14: +1:33
++         _0 = const {transmute(0x7fffffff): char}; // scope 1 at $DIR/transmute.rs:+1:14: +1:33
+          return;                          // scope 0 at $DIR/transmute.rs:+2:2: +2:2
+      }
+  }
+  

tests/mir-opt/const_prop/transmute.invalid_char.ConstProp.64bit.diff

@@ -0,0 +1,23 @@
+- // MIR for `less_as_i8` before ConstProp
++ // MIR for `less_as_i8` after ConstProp
+  
+  fn less_as_i8() -> i8 {
+      let mut _0: i8;                      // return place in scope 0 at $DIR/transmute.rs:+0:24: +0:26
+      let mut _1: std::cmp::Ordering;      // in scope 0 at $DIR/transmute.rs:+1:24: +1:48
+      scope 1 {
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 1 at $DIR/transmute.rs:+1:24: +1:48
+-         _1 = Less;                       // scope 1 at $DIR/transmute.rs:+1:24: +1:48
+-         _0 = move _1 as i8 (Transmute);  // scope 1 at $DIR/transmute.rs:+1:14: +1:49
++         _1 = const Less;                 // scope 1 at $DIR/transmute.rs:+1:24: +1:48
++                                          // mir::Constant
++                                          // + span: no-location
++                                          // + literal: Const { ty: std::cmp::Ordering, val: Value(Scalar(0xff)) }
++         _0 = const -1_i8;                // scope 1 at $DIR/transmute.rs:+1:14: +1:49
+          StorageDead(_1);                 // scope 1 at $DIR/transmute.rs:+1:48: +1:49
+          return;                          // scope 0 at $DIR/transmute.rs:+2:2: +2:2
+      }
+  }
+