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Rollup merge of #82176 - RalfJung:mir-fn-ptr-pretty, r=oli-obk

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fix MIR fn-ptr pretty-printing

An uninitialized function pointer would get printed as `{{uninit  fn()}` (notice the unbalanced parentheses), and a dangling fn ptr would ICE. This fixes both of that.

However, I have no idea how to add tests for this.

Also, I don't understand this MIR pretty-printing code. Somehow the print function `pretty_print_const_scalar` actually *returns* a transformed form of the const (but there is no doc comment explaining what is being returned); some match arms do `p!` while others do `self =`, and there's a wild mixture of `p!` and `write!`... all very mysterious and confusing.^^

r? ``@oli-obk``
This commit is contained in:
Guillaume Gomez 2021-02-20 20:37:00 +01:00 committed by GitHub
commit 2d39300e2f
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2 changed files with 13 additions and 10 deletions
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21
compiler/rustc_middle/src/ty/print/pretty.rs
View File

@ -1018,7 +1018,7 @@ pub trait PrettyPrinter<'tcx>:
p!(write("{:?}", char::try_from(int).unwrap()))
}
// Raw pointers
(Scalar::Int(int), ty::RawPtr(_)) => {
(Scalar::Int(int), ty::RawPtr(_) | ty::FnPtr(_)) => {
let data = int.assert_bits(self.tcx().data_layout.pointer_size);
self = self.typed_value(
|mut this| {
@ -1030,15 +1030,18 @@ pub trait PrettyPrinter<'tcx>:
)?;
}
(Scalar::Ptr(ptr), ty::FnPtr(_)) => {
// FIXME: this can ICE when the ptr is dangling or points to a non-function.
// We should probably have a helper method to share code with the "Byte strings"
// FIXME: We should probably have a helper method to share code with the "Byte strings"
// printing above (which also has to handle pointers to all sorts of things).
let instance = self.tcx().global_alloc(ptr.alloc_id).unwrap_fn();
self = self.typed_value(
|this| this.print_value_path(instance.def_id(), instance.substs),
|this| this.print_type(ty),
" as ",
)?;
match self.tcx().get_global_alloc(ptr.alloc_id) {
Some(GlobalAlloc::Function(instance)) => {
self = self.typed_value(
|this| this.print_value_path(instance.def_id(), instance.substs),
|this| this.print_type(ty),
" as ",
)?;
}
_ => self = self.pretty_print_const_pointer(ptr, ty, print_ty)?,
}
}
// For function type zsts just printing the path is enough
(Scalar::Int(int), ty::FnDef(d, s)) if int == ScalarInt::ZST => {

2
compiler/rustc_mir/src/interpret/operand.rs
View File

@ -112,7 +112,7 @@ impl<Tag: Copy> std::fmt::Display for ImmTy<'tcx, Tag> {
}
ScalarMaybeUninit::Uninit => cx.typed_value(
|mut this| {
this.write_str("{uninit ")?;
this.write_str("uninit ")?;
Ok(this)
},
|this| this.print_type(ty),