mirror of https://github.com/rust-lang/rust
79611d90b6
Added "copy" to Debug fmt for copy operands
In MIR's debug mode (--emit mir) the printing for Operands is slightly inconsistent.
The RValues - values on the right side of an Assign - are usually printed with their Operand when they are Places.
Example:
_2 = move _3
But for arguments, the operand is omitted.
_2 = _1
I propose a change be made, to display the place with the operand.
_2 = copy _1
Move and copy have different semantics, meaning this difference is important and helpful to the user. It also adds consistency to the pretty printing.
-- EDIT --
Consider this example Rust program and its MIR output with the **updated pretty printer.**
This was generated with the arguments --emit mir --crate-type lib -Zmir-opt-level=0 (Otherwise, it's optimised away since it's a junk program).
```rust
fn main(foo: i32) {
let v = 10;
if v == 20 {
foo;
}
else {
v;
}
}
```
```MIR
// WARNING: This output format is intended for human consumers only
// and is subject to change without notice. Knock yourself out.
fn main(_1: i32) -> () {
debug foo => _1;
let mut _0: ();
let _2: i32;
let mut _3: bool;
let mut _4: i32;
let _5: i32;
let _6: i32;
scope 1 {
debug v => _2;
}
bb0: {
StorageLive(_2);
_2 = const 10_i32;
StorageLive(_3);
StorageLive(_4);
_4 = copy _2;
_3 = Eq(move _4, const 20_i32);
switchInt(move _3) -> [0: bb2, otherwise: bb1];
}
bb1: {
StorageDead(_4);
StorageLive(_5);
_5 = copy _1;
StorageDead(_5);
_0 = const ();
goto -> bb3;
}
bb2: {
StorageDead(_4);
StorageLive(_6);
_6 = copy _2;
StorageDead(_6);
_0 = const ();
goto -> bb3;
}
bb3: {
StorageDead(_3);
StorageDead(_2);
return;
}
}
```
In this example program, we can see that when we move a place, it is preceded by "move". e.g. ``` _3 = Eq(move _4, const 20_i32);```. However, when we copy a place such as ```_5 = _1;```, it is not preceded by the operand in the original printout. I propose to change the print to include the copy ```_5 = copy _1``` as in this example.
Regarding the arguments part. When I originally submitted this PR, I was under the impression this only affected the print for arguments to a function, but actually, it affects anything that uses a copy. This is preferable anyway with regard to consistency. The PR is about making ```copy``` explicit.
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| .. | ||
| bool_compare.eq_false.InstSimplify-after-simplifycfg.diff | ||
| bool_compare.eq_true.InstSimplify-after-simplifycfg.diff | ||
| bool_compare.false_eq.InstSimplify-after-simplifycfg.diff | ||
| bool_compare.false_ne.InstSimplify-after-simplifycfg.diff | ||
| bool_compare.ne_false.InstSimplify-after-simplifycfg.diff | ||
| bool_compare.ne_true.InstSimplify-after-simplifycfg.diff | ||
| bool_compare.rs | ||
| bool_compare.true_eq.InstSimplify-after-simplifycfg.diff | ||
| bool_compare.true_ne.InstSimplify-after-simplifycfg.diff | ||
| casts.redundant.InstSimplify-after-simplifycfg.diff | ||
| casts.roundtrip.InstSimplify-after-simplifycfg.diff | ||
| casts.rs | ||
| combine_array_len.norm2.InstSimplify-after-simplifycfg.panic-abort.diff | ||
| combine_array_len.norm2.InstSimplify-after-simplifycfg.panic-unwind.diff | ||
| combine_array_len.rs | ||
| combine_clone_of_primitives.rs | ||
| combine_clone_of_primitives.{impl#0}-clone.InstSimplify-after-simplifycfg.panic-abort.diff | ||
| combine_clone_of_primitives.{impl#0}-clone.InstSimplify-after-simplifycfg.panic-unwind.diff | ||
| combine_transmutes.adt_transmutes.InstSimplify-after-simplifycfg.diff | ||
| combine_transmutes.identity_transmutes.InstSimplify-after-simplifycfg.diff | ||
| combine_transmutes.integer_transmutes.InstSimplify-after-simplifycfg.diff | ||
| combine_transmutes.rs | ||
| duplicate_switch_targets.assert_zero.InstSimplify-after-simplifycfg.diff | ||
| duplicate_switch_targets.rs | ||
| intrinsic_asserts.generic.InstSimplify-after-simplifycfg.diff | ||
| intrinsic_asserts.generic_ref.InstSimplify-after-simplifycfg.diff | ||
| intrinsic_asserts.panics.InstSimplify-after-simplifycfg.diff | ||
| intrinsic_asserts.removable.InstSimplify-after-simplifycfg.diff | ||
| intrinsic_asserts.rs | ||
| ref_of_deref.pointers.InstSimplify-after-simplifycfg.diff | ||
| ref_of_deref.references.InstSimplify-after-simplifycfg.diff | ||
| ref_of_deref.rs | ||
| ub_check.rs | ||
| ub_check.unwrap_unchecked.InstSimplify-after-simplifycfg.diff | ||