refactor to remove trans::adt and make rustc::ty::layout authoritative #36151

ahicks92 · 2016-08-30T22:54:51Z

I asked on IRC about optimizing struct layout by reordering fields from most-aligned to least-aligned and somehow ended up getting talked into doing this. The goal here is to make layout authoritative and to remove adt. The former has been accomplished by reimplementing represent_type_uncached and the latter is in progress. @eddyb thought I should make the PR now.

My plan is to reserve the actual optimization for a second PR, as this work is useful by itself.

rust-highfive · 2016-08-30T22:54:58Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @arielb1 (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

eddyb · 2016-08-30T22:56:06Z

r? @eddyb

eddyb · 2016-08-31T11:15:54Z

src/librustc_trans/adt.rs

+                               from: &layout::Struct,
+                               size: layout::Size,
+                               variant: Option<ty::VariantDef<'tcx>>,
+                               substs: &Substs<'tcx>)->Struct<'tcx> {


The arguments should be indented 4 more to the right (to align with tcx: ...) and there should be spaces around ->.

ahicks92 · 2016-08-31T16:45:09Z

I've incorporated the stylistic fixes from @eddyb. For some reason, make tidy is insisting that all source files are binary, so we'll see if the buildbot does that again. I need to find out what it's looking for. This did pick up a few lines that were too long. I'll try to be more careful about indentation in future.

The Case struct has now died.

I'm going to continue by trying to get debuginfo to use layout instead of adt, but may need help. I tripped on it yesterday, but I think that I started trying to refactor it from the wrong place. This then caused one small change to it to actually be rather large in scope. I think that starting from somewhere different might allow me to do it without having to keep the whole module in my head.

I can't continue this until either late this evening or tomorrow.

arielb1 · 2016-08-31T16:51:31Z

src/librustc/ty/layout.rs

@@ -939,10 +939,8 @@ impl<'a, 'gcx, 'tcx> Layout {
                    }
                }

-                if def.variants.len() == 1 {
+                if def.variants.len() == 1 && hint == attr::ReprAny{


nit: missing space after attr::ReprAny

ahicks92 · 2016-09-13T00:57:54Z

@arielb1
I'll look at the overflow stuff. @eddyb told me he thought layout was already handling the case of types that are too big to fit in the address space.

ahicks92 · 2016-09-13T01:00:11Z

@arielb1
Nevermind, I'm being an idiot. I see what you mean in regards to not catching it. I suppose that the solution here is to spit out a compiler error. Where do I need to look to understand how to go about doing this?

eddyb · 2016-09-13T01:03:19Z

@camlorn Look for how we check for size overflows when computing the LLVM types.
CrateContext::layout_of needs to do that error reporting, AFAICT.

arielb1 · 2016-09-14T15:50:56Z

Needs rebase

arielb1 · 2016-09-14T15:51:37Z

src/librustc/ty/context.rs

@@ -496,6 +496,9 @@ pub struct GlobalCtxt<'tcx> {
    /// Cache for layouts computed from types.
    pub layout_cache: RefCell<FnvHashMap<Ty<'tcx>, &'tcx Layout>>,

+    //Used to prevent layout from recursing too deeply.


nit: don't put random mutable parameters on the tcx. Use a LayoutContext.

You can't, because the recursion doesn't go through a dedicated context. You might be able to put it in TargetDataLayout, I guess, but that's about it.

Space after //. Also, /// should be used (signifying doc comments).

eddyb · 2016-09-18T10:33:27Z

src/librustc_trans/adt.rs

+                layout::Size::from_bytes(i*element_size.bytes())
+            }).collect::<Vec<_>>();
+            let contents = build_const_struct(ccx, &offsets[..], vals, true);
+            C_struct(ccx, &contents[..], true)


It shouldn't be C_struct but rather a LLVM vector type.

It was C_struct before, as layout::Vector went to Repr::Univariant. I'll see if I can figure out how to change this. But I half-suspect it'll cause all the simd tests to start failing (presumably LLVM treats vector types differently and presumably other stuff still assumes it's whatever C_struct does).

It shouldn't have gone through Repr, I don't think. Ah, but it's fine because of the way we handle constants, that is, we cast a pointer to a location holding the constant, because enum variants aren't the type of the enum (and in this case, structs instead of vectors).

Are you saying leave it or change it? I follow your explanation, but I'm not sure if you still consider it a problem worthy of being fixed.

It's fine to leave it as it was before, however, it may actually cleaner to use a (LLVM) vector and not generate the Vec of field types.

eddyb · 2016-09-20T08:30:14Z

src/librustc_trans/adt.rs

+        1 => Type::array(&Type::i8(cx), align_units),
+        2 => Type::array(&Type::i16(cx), align_units),
+        4 => Type::array(&Type::i32(cx), align_units),
+        8 if machine::llalign_of_min(cx, Type::i64(cx)) == 8 =>


This can use cx.tcx().data_layout.i64_align.abi() - in fact, look in ty::layout for how a similar match (for enums) was turned into a more general thing (e.g. there are architectures where i32 doesn't have an alignment of 4).

bors · 2016-09-22T02:20:01Z

☔ The latest upstream changes (presumably #36496) made this pull request unmergeable. Please resolve the merge conflicts.

ahicks92 · 2016-09-23T03:22:27Z

Repr is dead.

Don't merge this yet. generic_type_of still needs cleanup. I may also go after Disr, but haven't looked to see how bad that is as of yet.

adt probably needs splitting, reorganization, and maybe outright elimination. I am open to suggestions as to what module(s) to create from it, but am perfectly fine with leaving it as it is (this PR now technically meets the goal of making layout authoritative and enabling us to more easily add optimizations).

Throw your comments in for additional cleanup, and I'll incorporate them. At this point, I'm not sure what all I should try to kill still, or if there's anything else I'm not getting an unused warning about that's not being called.

eddyb · 2016-09-23T09:06:25Z

src/librustc_trans/adt.rs

    }
 }

 fn struct_field_ptr<'blk, 'tcx>(bcx: &BlockAndBuilder<'blk, 'tcx>,
-                                st: &Struct<'tcx>, val: MaybeSizedValue,
+                                st: &layout::Struct, fields: &Vec<Ty<'tcx>>, val: MaybeSizedValue,


Creating vectors is expensive. This function should use the layout::Struct to get the offset of the last field instead.

…ith it.

…rements

eddyb

Great job! Mostly only formatting nitpicks left.

eddyb · 2016-09-25T03:39:36Z

src/librustc/ty/layout.rs

@@ -328,6 +328,43 @@ pub enum Integer {
 }

 impl Integer {
+


Extra newline.

eddyb · 2016-09-25T03:40:06Z

src/librustc/ty/layout.rs

+    }
+
+    pub fn to_ty<'a, 'tcx>(&self, tcx: &ty::TyCtxt<'a, 'tcx, 'tcx>,
+                       signed: bool) -> Ty<'tcx> {


signed is aligned 4 spaces to the left of where it should be.

eddyb · 2016-09-25T03:40:52Z

src/librustc/ty/layout.rs

@@ -350,6 +387,18 @@ impl Integer {
        }
    }

+    //Find the smallest integer with the given alignment.


Space after // and use ///.

eddyb · 2016-09-25T03:42:47Z

src/librustc/ty/layout.rs

@@ -1003,6 +1061,16 @@ impl<'a, 'gcx, 'tcx> Layout {
                    }
                }

+                if def.variants.len() == 1 && hint == attr::ReprAny{


Missing space before {. Also, this will never be reached, maybe you meant to put the hint == attr::ReprAny in the previous if?

eddyb · 2016-09-25T03:43:33Z

src/librustc_trans/adt.rs

+//Given an enum, struct, closure, or tuple, extracts fields.
+//treats closures as a struct with one variant.
+//`empty_if_no_variants` is a switch to deal with empty enums.
+//if true, `variant_index` is disregarded and an empty Vec returned in this case.


Same: space after // and make it /// for doc comments.

eddyb · 2016-09-25T03:48:03Z

src/librustc_trans/adt.rs

-        General(ity, _) => {
-            C_integral(ll_inttype(bcx.ccx(), ity), discr.0, true)
+        layout::RawNullablePointer { .. } |
+layout::StructWrappedNullablePointer { .. } => {


Missing alignment on this line.

eddyb · 2016-09-25T03:51:20Z

src/librustc_trans/adt.rs

+    for (&val, target_offset) in
+        vals.iter().zip(
+        offset_after_field.iter().map(|i| i.bytes())
+    ) {


You can put the second iterator in a target_offsets variable to recover the original look.

eddyb · 2016-09-25T03:52:44Z

src/librustc_trans/debuginfo/metadata.rs

@@ -1292,11 +1291,15 @@ impl<'tcx> EnumMemberDescriptionFactory<'tcx> {
    fn create_member_descriptions<'a>(&self, cx: &CrateContext<'a, 'tcx>)
                                      -> Vec<MemberDescription> {
        let adt = &self.enum_type.ty_adt_def().unwrap();
+        let substs = match self.enum_type.sty {
+            ty::TyAdt(def, ref s) if def.adt_kind() == AdtKind::Enum => s,
+            ref t @ _ => bug!("{} is not an enum", t)


Print self.enum_type instead of the sty.

eddyb · 2016-09-25T03:54:28Z

src/librustc_trans/mir/constant.rs

@@ -735,7 +733,12 @@ impl<'a, 'tcx> MirConstContext<'a, 'tcx> {

                let base = match tr_lvalue.base {
                    Base::Value(llval) => {
-                        let align = type_of::align_of(self.ccx, ty);
+                        //Fixme: may be wrong for &*(&simd_vec as &fmt::Debug)


Space after // and FIXME.

eddyb · 2016-09-25T03:55:24Z

src/librustc_trans/type_.rs

+        }
+    }
+
+    pub fn from_primitive(ccx: &CrateContext, p: layout::Primitive)->Type {


Same -> thing here.

eddyb · 2016-09-26T00:16:22Z

@bors r+

bors · 2016-09-26T00:16:23Z

📌 Commit 467454b has been approved by eddyb

bors · 2016-09-26T01:47:01Z

⌛ Testing commit 467454b with merge 9966397...

@eddyb

refactor to remove trans::adt and make rustc::ty::layout authoritative I asked on IRC about optimizing struct layout by reordering fields from most-aligned to least-aligned and somehow ended up getting talked into doing this. The goal here is to make `layout` authoritative and to remove `adt`. The former has been accomplished by reimplementing `represent_type_uncached` and the latter is in progress. @eddyb thought I should make the PR now. My plan is to reserve the actual optimization for a second PR, as this work is useful by itself.

bors · 2016-09-26T05:03:26Z

rust-highfive assigned arielb1 Aug 30, 2016

rust-highfive assigned eddyb and unassigned arielb1 Aug 30, 2016

eddyb reviewed Aug 31, 2016
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ahicks92 force-pushed the struct_layout_optimization branch 2 times, most recently from 8036624 to f76321e Compare August 31, 2016 16:35

arielb1 reviewed Aug 31, 2016
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arielb1 reviewed Sep 14, 2016
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ahicks92 force-pushed the struct_layout_optimization branch from 1094330 to 0561f6f Compare September 16, 2016 20:46

eddyb reviewed Sep 18, 2016

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eddyb suggested changes Sep 20, 2016

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ahicks92 force-pushed the struct_layout_optimization branch from 1d6e735 to cfadf74 Compare September 23, 2016 00:14

eddyb reviewed Sep 23, 2016

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ahicks92 added 3 commits September 24, 2016 18:21

Completely kill represent_type and the adt::Repr type that goes w…

f16068e

…ith it.

Optimize struct_field_ptr

4038189

Clean up matches that determine integers for specific alignment requi…

12ff05f

…rements

ahicks92 force-pushed the struct_layout_optimization branch from c2f8e12 to 12ff05f Compare September 24, 2016 22:26

ahicks92 mentioned this pull request Sep 25, 2016

make tidy: skip check for binaries if /proc/version contains the string Microsoft #36706

Closed

Update codegen/link_section.rs.

f2f7ace

eddyb suggested changes Sep 25, 2016

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Incorporate review comments.

467454b

ahicks92 force-pushed the struct_layout_optimization branch from aa83877 to 467454b Compare September 26, 2016 00:14

eddyb approved these changes Sep 26, 2016

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bors merged commit 467454b into rust-lang:master Sep 26, 2016

ahicks92 deleted the struct_layout_optimization branch September 26, 2016 15:11

TimNN mentioned this pull request Oct 16, 2016

ICE on with #[repr(..)] for single-variant enum #34571

Closed

refactor to remove trans::adt and make rustc::ty::layout authoritative #36151

refactor to remove trans::adt and make rustc::ty::layout authoritative #36151

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ahicks92 commented Aug 30, 2016

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eddyb commented Sep 26, 2016

bors commented Sep 26, 2016

bors commented Sep 26, 2016

bors commented Sep 26, 2016

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