Auto merge of #59397 - kennytm:rollup, r=kennytm

Rollup of 7 pull requests

Successful merges:

 - #59213 (Track changes to robots.txt)
 - #59239 (Remove inline assembly from hint::spin_loop)
 - #59251 (Use a valid name for graphviz graphs)
 - #59296 (Do not encode gensymed imports in metadata)
 - #59328 (Implement specialized nth_back() for Box and Windows.)
 - #59355 (Fix ICE with const generic param in struct)
 - #59377 (Correct minimum system LLVM version in tests)

Author: bors

src/doc/robots.txt

@@ -0,0 +1,19 @@
+# NB: This file is not automatically deployed. After changes, it needs to be uploaded manually to doc.rust-lang.org
+User-agent: *
+Disallow: /0.3/
+Disallow: /0.4/
+Disallow: /0.5/
+Disallow: /0.6/
+Disallow: /0.7/
+Disallow: /0.8/
+Disallow: /0.9/
+Disallow: /0.10/
+Disallow: /0.11.0/
+Disallow: /0.12.0/
+Disallow: /1.0.0-alpha/
+Disallow: /1.0.0-alpha.2/
+Disallow: /1.0.0-beta/
+Disallow: /1.0.0-beta.2/
+Disallow: /1.0.0-beta.3/
+Disallow: /1.0.0-beta.4/
+Disallow: /1.0.0-beta.5/

src/liballoc/boxed.rs

@@ -677,6 +677,9 @@ impl<I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<I> {
     fn next_back(&mut self) -> Option<I::Item> {
         (**self).next_back()
     }
+    fn nth_back(&mut self, n: usize) -> Option<I::Item> {
+        (**self).nth_back(n)
+    }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I> {

src/liballoc/lib.rs

@@ -115,6 +115,7 @@
 #![feature(maybe_uninit, maybe_uninit_slice, maybe_uninit_array)]
 #![feature(alloc_layout_extra)]
 #![feature(try_trait)]
+#![feature(iter_nth_back)]
 
 // Allow testing this library
 

src/libcore/hint.rs

@@ -62,13 +62,32 @@ pub unsafe fn unreachable_unchecked() -> ! {
 #[inline]
 #[unstable(feature = "renamed_spin_loop", issue = "55002")]
 pub fn spin_loop() {
-    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
-    unsafe {
-        asm!("pause" ::: "memory" : "volatile");
+    #[cfg(
+        all(
+            any(target_arch = "x86", target_arch = "x86_64"),
+            target_feature = "sse2"
+        )
+    )] {
+        #[cfg(target_arch = "x86")] {
+            unsafe { crate::arch::x86::_mm_pause() };
+        }
+
+        #[cfg(target_arch = "x86_64")] {
+            unsafe { crate::arch::x86_64::_mm_pause() };
+        }
     }
 
-    #[cfg(target_arch = "aarch64")]
-    unsafe {
-        asm!("yield" ::: "memory" : "volatile");
+    #[cfg(
+        any(
+            target_arch = "aarch64",
+            all(target_arch = "arm", target_feature = "v6")
+        )
+    )] {
+        #[cfg(target_arch = "aarch64")] {
+            unsafe { crate::arch::aarch64::__yield() };
+        }
+        #[cfg(target_arch = "arm")] {
+            unsafe { crate::arch::arm::__yield() };
+        }
     }
 }

src/libcore/slice/mod.rs

@@ -3867,6 +3867,19 @@ impl<'a, T> DoubleEndedIterator for Windows<'a, T> {
             ret
         }
     }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        let (end, overflow) = self.v.len().overflowing_sub(n);
+        if end < self.size || overflow {
+            self.v = &[];
+            None
+        } else {
+            let ret = &self.v[end-self.size..end];
+            self.v = &self.v[..end-1];
+            Some(ret)
+        }
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]

src/libcore/tests/slice.rs

@@ -578,6 +578,19 @@ fn test_windows_nth() {
     assert_eq!(c2.next(), None);
 }
 
+#[test]
+fn test_windows_nth_back() {
+    let v: &[i32] = &[0, 1, 2, 3, 4, 5];
+    let mut c = v.windows(2);
+    assert_eq!(c.nth_back(2).unwrap()[0], 2);
+    assert_eq!(c.next_back().unwrap()[1], 2);
+
+    let v2: &[i32] = &[0, 1, 2, 3, 4];
+    let mut c2 = v2.windows(4);
+    assert_eq!(c2.nth_back(1).unwrap()[1], 1);
+    assert_eq!(c2.next_back(), None);
+}
+
 #[test]
 fn test_windows_last() {
     let v: &[i32] = &[0, 1, 2, 3, 4, 5];

src/librustc_codegen_llvm/debuginfo/metadata.rs

@@ -1156,12 +1156,14 @@ fn prepare_union_metadata(
 // Enums
 //=-----------------------------------------------------------------------------
 
-// DWARF variant support is only available starting in LLVM 7.
+// DWARF variant support is only available starting in LLVM 8.
 // Although the earlier enum debug info output did not work properly
 // in all situations, it is better for the time being to continue to
 // sometimes emit the old style rather than emit something completely
-// useless when rust is compiled against LLVM 6 or older.  This
-// function decides which representation will be emitted.
+// useless when rust is compiled against LLVM 6 or older. LLVM 7
+// contains an early version of the DWARF variant support, and will
+// crash when handling the new debug info format. This function
+// decides which representation will be emitted.
 fn use_enum_fallback(cx: &CodegenCx<'_, '_>) -> bool {
     // On MSVC we have to use the fallback mode, because LLVM doesn't
     // lower variant parts to PDB.

src/librustc_driver/pretty.rs

@@ -633,10 +633,20 @@ fn print_flowgraph<'a, 'tcx, W: Write>(variants: Vec<borrowck_dot::Variant>,
     let body = tcx.hir().body(body_id);
     let cfg = cfg::CFG::new(tcx, &body);
     let labelled_edges = mode != PpFlowGraphMode::UnlabelledEdges;
+    let hir_id = code.id();
+    // We have to disassemble the hir_id because name must be ASCII
+    // alphanumeric. This does not appear in the rendered graph, so it does not
+    // have to be user friendly.
+    let name = format!(
+        "hir_id_{}_{}_{}",
+        hir_id.owner.address_space().index(),
+        hir_id.owner.as_array_index(),
+        hir_id.local_id.index(),
+    );
     let lcfg = LabelledCFG {
         tcx,
         cfg: &cfg,
-        name: format!("node_{}", code.id()),
+        name,
         labelled_edges,
     };
 

src/librustc_mir/borrow_check/mod.rs

@@ -156,7 +156,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
     let mut flow_inits = FlowAtLocation::new(do_dataflow(
         tcx,
         mir,
-        id,
+        def_id,
         &attributes,
         &dead_unwinds,
         MaybeInitializedPlaces::new(tcx, mir, &mdpe),
@@ -191,7 +191,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
     let flow_borrows = FlowAtLocation::new(do_dataflow(
         tcx,
         mir,
-        id,
+        def_id,
         &attributes,
         &dead_unwinds,
         Borrows::new(tcx, mir, regioncx.clone(), &borrow_set),
@@ -200,7 +200,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
     let flow_uninits = FlowAtLocation::new(do_dataflow(
         tcx,
         mir,
-        id,
+        def_id,
         &attributes,
         &dead_unwinds,
         MaybeUninitializedPlaces::new(tcx, mir, &mdpe),
@@ -209,7 +209,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
     let flow_ever_inits = FlowAtLocation::new(do_dataflow(
         tcx,
         mir,
-        id,
+        def_id,
         &attributes,
         &dead_unwinds,
         EverInitializedPlaces::new(tcx, mir, &mdpe),

src/librustc_mir/dataflow/graphviz.rs

@@ -1,20 +1,22 @@
 //! Hook into libgraphviz for rendering dataflow graphs for MIR.
 
-use rustc::hir::HirId;
+use rustc::hir::def_id::DefId;
 use rustc::mir::{BasicBlock, Mir};
 
 use std::fs;
 use std::io;
 use std::marker::PhantomData;
 use std::path::Path;
 
+use crate::util::graphviz_safe_def_name;
+
 use super::{BitDenotation, DataflowState};
 use super::DataflowBuilder;
 use super::DebugFormatted;
 
 pub trait MirWithFlowState<'tcx> {
     type BD: BitDenotation<'tcx>;
-    fn hir_id(&self) -> HirId;
+    fn def_id(&self) -> DefId;
     fn mir(&self) -> &Mir<'tcx>;
     fn flow_state(&self) -> &DataflowState<'tcx, Self::BD>;
 }
@@ -23,7 +25,7 @@ impl<'a, 'tcx, BD> MirWithFlowState<'tcx> for DataflowBuilder<'a, 'tcx, BD>
     where BD: BitDenotation<'tcx>
 {
     type BD = BD;
-    fn hir_id(&self) -> HirId { self.hir_id }
+    fn def_id(&self) -> DefId { self.def_id }
     fn mir(&self) -> &Mir<'tcx> { self.flow_state.mir() }
     fn flow_state(&self) -> &DataflowState<'tcx, Self::BD> { &self.flow_state.flow_state }
 }
@@ -47,8 +49,8 @@ pub(crate) fn print_borrowck_graph_to<'a, 'tcx, BD, P>(
     let g = Graph { mbcx, phantom: PhantomData, render_idx };
     let mut v = Vec::new();
     dot::render(&g, &mut v)?;
-    debug!("print_borrowck_graph_to path: {} hir_id: {}",
-           path.display(), mbcx.hir_id);
+    debug!("print_borrowck_graph_to path: {} def_id: {:?}",
+           path.display(), mbcx.def_id);
     fs::write(path, v)
 }
 
@@ -69,9 +71,8 @@ impl<'a, 'tcx, MWF, P> dot::Labeller<'a> for Graph<'a, 'tcx, MWF, P>
     type Node = Node;
     type Edge = Edge;
     fn graph_id(&self) -> dot::Id<'_> {
-        dot::Id::new(format!("graph_for_node_{}",
-                             self.mbcx.hir_id()))
-            .unwrap()
+        let name = graphviz_safe_def_name(self.mbcx.def_id());
+        dot::Id::new(format!("graph_for_def_id_{}", name)).unwrap()
     }
 
     fn node_id(&self, n: &Node) -> dot::Id<'_> {