Convert Const to Allocation in smir #114587

ouz-a · 2023-08-07T15:35:20Z

Continuation of previous pr #114466

cc rust-lang/project-stable-mir#15

r? @oli-obk

rustbot · 2023-08-07T15:35:29Z

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

This PR changes Stable MIR

cc @oli-obk, @celinval, @spastorino

oli-obk · 2023-08-07T15:43:40Z

compiler/rustc_smir/src/stable_mir/ty.rs

+                .align;
+            Allocation::new_empty_allocation(align.abi)
+        }
+        ConstValue::Slice { data, start: _, end: _ } => data.0.stable(tables),


this is wrong. the allocation refers to what the slice points to, not to the slice pointer itself. maybe just make the entire thing opaque?

oli-obk · 2023-08-07T15:44:02Z

compiler/rustc_smir/src/stable_mir/ty.rs

+            Allocation::new_empty_allocation(align.abi)
+        }
+        ConstValue::Slice { data, start: _, end: _ } => data.0.stable(tables),
+        ConstValue::ByRef { alloc, offset: _ } => alloc.0.stable(tables),


you lost the offset. You only want the bytes starting at offset

oli-obk · 2023-08-07T15:45:23Z

compiler/rustc_smir/src/stable_mir/ty.rs

+            let size = scalar.size();
+            let align = tables
+                .tcx
+                .layout_of(rustc_middle::ty::ParamEnv::empty().and(const_kind.ty()))


Suggested change

.layout_of(rustc_middle::ty::ParamEnv::empty().and(const_kind.ty()))

.layout_of(rustc_middle::ty::ParamEnv::reveal_all().and(const_kind.ty()))

compiler/rustc_smir/src/stable_mir/ty.rs

RalfJung · 2023-08-07T15:48:33Z

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -326,7 +326,7 @@ impl<Prov: Provenance, Bytes: AllocBytes> Allocation<Prov, (), Bytes> {
    }

    /// Try to create an Allocation of `size` bytes, panics if there is not enough memory
-    /// available to the compiler to do so.
+    /// available to the compiler to do so. Also used for creating dummy `Allocation`.


What's a dummy allocation?

The comment change is confusing me.

Maybe I should documented as

can be used for creating allocations out of Scalar values,

because from the current doc I couldn't understand I could do that I had to ask oli about it. It's very hard to understand what functions do or when to use them when you are foreign some part of the compiler.

edit:tl;dr: my intention is to make the doc more beginner friendly.

I think what you are asking for is a complete tutorial on the data model of the CTFE interpreter and its memory. That's reasonable, this should ideally be documented somewhere, but fn uninit is not the right place for that.

There's nothing specific about uninit that makes it more or less suited for "dummy" allocations so I think this comment change should be removed. Also note that "converting a Scalar to an Allocation" is an extremely uncommon usecase, so it might not be a good idea to gear the documentation towards that.

You could say something general like, "To obtain an allocation filled with specific data, first call this function and then call write_scalar to fill in the right data."

Now on second thought, you are right maybe someone could explain these topics in depth in rustc dev guide

bors · 2023-08-07T19:06:19Z

☔ The latest upstream changes (presumably #114585) made this pull request unmergeable. Please resolve the merge conflicts.

oli-obk · 2023-08-08T10:22:53Z

compiler/rustc_smir/src/stable_mir/ty.rs

+        }
+        ConstValue::ByRef { alloc, offset } => {
+            let size = alloc.0.size();
+            let bytes = alloc.0.get_bytes_unchecked(alloc_range(offset, offset + size));


for a 10 element slice at offset 4 this is now going to take elements 4..14, which don't exist.

Also, I just remembered that you may want to use the type size, instead of everything from offset to the end.

compiler/rustc_smir/src/stable_mir/ty.rs

oli-obk · 2023-08-09T13:23:28Z

compiler/rustc_smir/src/stable_mir/ty.rs

+                .layout_of(rustc_middle::ty::ParamEnv::reveal_all().and(const_kind.ty()))
+                .unwrap()
+                .size;
+            let bytes = alloc.0.get_bytes_unchecked(alloc_range(offset, ty_size));


This loses the initialization information and the relocation information. It may be easier to pull out the logic of the stable method for Allocation to be able to call it with arbitrary allocation ranges (and have the stable method always take the entire range). For the initialization information, nothing would change, your existing logic would work if the ranges in the for loop are adjusted. For relocations you'd need to remap the offsets and remove all things that are out of range.

oli-obk · 2023-08-09T18:11:53Z

@bors r+

bors · 2023-08-09T18:11:55Z

📌 Commit 8f1ea57 has been approved by oli-obk

It is now in the queue for this repository.

oli-obk · 2023-08-09T18:12:28Z

@bors rollup

spastorino · 2023-08-09T19:13:03Z

#114599 is already approved and was rolled up too.

This PR won't merge cleanly in a rollup with #114599.

@bors rollup-

I can do a rollup again once #114599 is merged in a rollup or if a rollup is not created before this one is in the top of the queue, this one is going to be merged first :).

…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#110435 (rustdoc-json: Add test for field ordering.) - rust-lang#111891 (feat: `riscv-interrupt-{m,s}` calling conventions) - rust-lang#114377 (test_get_dbpath_for_term(): handle non-utf8 paths (fix FIXME)) - rust-lang#114469 (Detect method not found on arbitrary self type with different mutability) - rust-lang#114587 (Convert Const to Allocation in smir) - rust-lang#114670 (Don't use `type_of` to determine if item has intrinsic shim) Failed merges: - rust-lang#114599 (Add impl trait declarations to SMIR) r? `@ghost` `@rustbot` modify labels: rollup

Make Const more useful in smir Since rust-lang#114587 is merged, we can make use of what we built and make Const more useful by making it not `Opaque` r? `@spastorino`

Add stable for Constant in smir Previously rust-lang#114587 we covered much of the groundwork needed to cover Const in smir, so there is no reason keep `Constant` as String. r? `@spastorino`

Add stable for Constant in smir Previously rust-lang/rust#114587 we covered much of the groundwork needed to cover Const in smir, so there is no reason keep `Constant` as String. r? `@spastorino`

…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#110435 (rustdoc-json: Add test for field ordering.) - rust-lang#111891 (feat: `riscv-interrupt-{m,s}` calling conventions) - rust-lang#114377 (test_get_dbpath_for_term(): handle non-utf8 paths (fix FIXME)) - rust-lang#114469 (Detect method not found on arbitrary self type with different mutability) - rust-lang#114587 (Convert Const to Allocation in smir) - rust-lang#114670 (Don't use `type_of` to determine if item has intrinsic shim) Failed merges: - rust-lang#114599 (Add impl trait declarations to SMIR) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned oli-obk Aug 7, 2023

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ouz-a force-pushed the smir_allocation branch from 87ce945 to 17355c4 Compare August 7, 2023 19:44

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Convert Const to Allocation in smir

c41339a

ouz-a force-pushed the smir_allocation branch from f7d2d66 to c41339a Compare August 9, 2023 12:00

oli-obk reviewed Aug 9, 2023

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only allocate bytes within AllocRange

8f1ea57

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 9, 2023

ouz-a mentioned this pull request Aug 9, 2023

Add constants to smir #114342

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matthiaskrgr mentioned this pull request Aug 9, 2023

Rollup of 6 pull requests #114673

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bors merged commit bbc1109 into rust-lang:master Aug 10, 2023
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rustbot added this to the 1.73.0 milestone Aug 10, 2023

ouz-a mentioned this pull request Aug 11, 2023

Make Const more useful in smir #114745

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ouz-a mentioned this pull request Aug 25, 2023

Add stable for Constant in smir #115202

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Convert Const to Allocation in smir #114587

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	.layout_of(rustc_middle::ty::ParamEnv::empty().and(const_kind.ty()))
	.layout_of(rustc_middle::ty::ParamEnv::reveal_all().and(const_kind.ty()))

Convert Const to Allocation in smir #114587

Convert Const to Allocation in smir #114587

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