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.
The mir-opt test format emits MIR to extra files that you can automatically update by specifying
--bless on the command line (just like ui tests updating .stderr files).
--blessable test format
By default 32 bit and 64 bit targets use the same dump files, which can be problematic in the
presence of pointers in constants or other bit width dependent things. In that case you can add
// EMIT_MIR_FOR_EACH_BIT_WIDTH
to your test, causing separate files to be generated for 32bit and 64bit systems.
Testing a particular MIR pass
If you are only testing the behavior of a particular mir-opt pass on some specific input (as is
usually the case), you should add
//@ test-mir-pass: PassName
to the top of the file. This makes sure that other passes don't run which means you'll get the input
you expected and your test won't break when other code changes. This also lets you test passes
that are disabled by default.
Emit a diff of the mir for a specific optimization
This is what you want most often when you want to see how an optimization changes the MIR.
// EMIT_MIR $file_name_of_some_mir_dump.diff
Emit mir after a specific optimization
Use this if you are just interested in the final state after an optimization.
// EMIT_MIR $file_name_of_some_mir_dump.after.mir
Emit mir before a specific optimization
This exists mainly for completeness and is rarely useful.
The LLVM FileCheck tool is used to verify the contents of output MIR against CHECK directives
present in the test file. This works on the runtime MIR, generated by --emit=mir, and not
on the output of a individual passes.
Use // skip-filecheck to prevent FileCheck from running.
To check MIR for function foo, start with a // CHECK-LABEL fn foo( directive.
{{regex}} syntax allows to match regex.
[[name:regex]] syntax allows to bind name to a string matching regex, and refer to it
as [[name]] in later directives, regex should be written not to match a leading space.
Use [[my_local:_.*]] to name a local, and [[my_bb:bb.*]] to name a block.
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