Rollup merge of rust-lang#54702 - RalfJung:fn-ptr-promotion, r=oli-obk

do not promote comparing function pointers

This *could* break existing code that relied on fn ptr comparison getting promoted to `'static` lifetime.

Fixes rust-lang#54696

src/librustc_mir/transform/qualify_consts.rs

@@ -750,7 +750,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
  }
 
  Rvalue::BinaryOp(op, ref lhs, _) => {
- if let ty::RawPtr(_) = lhs.ty(self.mir, self.tcx).sty {
+ if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.mir, self.tcx).sty {
  assert!(op == BinOp::Eq || op == BinOp::Ne ||
  op == BinOp::Le || op == BinOp::Lt ||
  op == BinOp::Ge || op == BinOp::Gt ||

src/librustc_passes/rvalue_promotion.rs

@@ -348,7 +348,7 @@ fn check_expr_kind<'a, 'tcx>(
  return NotPromotable;
  }
  match v.tables.node_id_to_type(lhs.hir_id).sty {
- ty::RawPtr(_) => {
+ ty::RawPtr(_) | ty::FnPtr(..) => {
  assert!(op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne ||
  op.node == hir::BinOpKind::Le || op.node == hir::BinOpKind::Lt ||
  op.node == hir::BinOpKind::Ge || op.node == hir::BinOpKind::Gt);

src/test/run-pass/issues/issue-54696.rs

@@ -0,0 +1,8 @@
+// run-pass
+
+fn main() {
+ // We shouldn't promote this
+ &(main as fn() == main as fn());
+ // Also check nested case
+ &(&(main as fn()) == &(main as fn()));
+}

src/test/ui/consts/const-eval/promoted_raw_ptr_ops.nll.stderr

@@ -14,7 +14,7 @@ error[E0716]: temporary value dropped while borrowed
  |
 LL | let y: &'static usize = &(&1 as *const i32 as usize + 1); //~ ERROR does not live long enough
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
-LL | let z: &'static i32 = &(unsafe { *(42 as *const i32) }); //~ ERROR does not live long enough
+...
 LL | }
  | - temporary value is freed at the end of this statement
  |
@@ -25,11 +25,22 @@ error[E0716]: temporary value dropped while borrowed
  |
 LL | let z: &'static i32 = &(unsafe { *(42 as *const i32) }); //~ ERROR does not live long enough
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
+LL | let a: &'static bool = &(main as fn() == main as fn()); //~ ERROR does not live long enough
+LL | }
+ | - temporary value is freed at the end of this statement
+ |
+ = note: borrowed value must be valid for the static lifetime...
+
+error[E0716]: temporary value dropped while borrowed
+ --> $DIR/promoted_raw_ptr_ops.rs:18:29
+ |
+LL | let a: &'static bool = &(main as fn() == main as fn()); //~ ERROR does not live long enough
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
 LL | }
  | - temporary value is freed at the end of this statement
  |
  = note: borrowed value must be valid for the static lifetime...
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0716`.

src/test/ui/consts/const-eval/promoted_raw_ptr_ops.rs

@@ -15,4 +15,5 @@ fn main() {
  //~^ ERROR does not live long enough
  let y: &'static usize = &(&1 as *const i32 as usize + 1); //~ ERROR does not live long enough
  let z: &'static i32 = &(unsafe { *(42 as *const i32) }); //~ ERROR does not live long enough
+ let a: &'static bool = &(main as fn() == main as fn()); //~ ERROR does not live long enough
 }

src/test/ui/consts/const-eval/promoted_raw_ptr_ops.stderr

@@ -14,7 +14,7 @@ error[E0597]: borrowed value does not live long enough
  |
 LL | let y: &'static usize = &(&1 as *const i32 as usize + 1); //~ ERROR does not live long enough
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ temporary value does not live long enough
-LL | let z: &'static i32 = &(unsafe { *(42 as *const i32) }); //~ ERROR does not live long enough
+...
 LL | }
  | - temporary value only lives until here
  |
@@ -25,11 +25,22 @@ error[E0597]: borrowed value does not live long enough
  |
 LL | let z: &'static i32 = &(unsafe { *(42 as *const i32) }); //~ ERROR does not live long enough
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ temporary value does not live long enough
+LL | let a: &'static bool = &(main as fn() == main as fn()); //~ ERROR does not live long enough
+LL | }
+ | - temporary value only lives until here
+ |
+ = note: borrowed value must be valid for the static lifetime...
+
+error[E0597]: borrowed value does not live long enough
+ --> $DIR/promoted_raw_ptr_ops.rs:18:29
+ |
+LL | let a: &'static bool = &(main as fn() == main as fn()); //~ ERROR does not live long enough
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ temporary value does not live long enough
 LL | }
  | - temporary value only lives until here
  |
  = note: borrowed value must be valid for the static lifetime...
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0597`.