code coverage foundation for hash and num_counters

Replaced dummy values for hash and num_counters with computed values,
and refactored InstrumentCoverage pass to simplify injecting more
counters per function in upcoming versions.

Improved usage documentation and error messaging.

src/librustc_codegen_llvm/intrinsic.rs

@@ -16,6 +16,7 @@ use rustc_codegen_ssa::common::TypeKind;
 use rustc_codegen_ssa::glue;
 use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
 use rustc_codegen_ssa::mir::place::PlaceRef;
+use rustc_codegen_ssa::mir::FunctionCx;
 use rustc_codegen_ssa::traits::*;
 use rustc_codegen_ssa::MemFlags;
 use rustc_hir as hir;
@@ -23,7 +24,6 @@ use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt};
 use rustc_middle::ty::{self, Ty};
 use rustc_middle::{bug, span_bug};
 use rustc_span::Span;
-use rustc_span::Symbol;
 use rustc_target::abi::{self, HasDataLayout, LayoutOf, Primitive};
 use rustc_target::spec::PanicStrategy;
 
@@ -82,14 +82,14 @@ fn get_simple_intrinsic(cx: &CodegenCx<'ll, '_>, name: &str) -> Option<&'ll Valu
 }
 
 impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
-    fn codegen_intrinsic_call(
+    fn codegen_intrinsic_call<'b, Bx: BuilderMethods<'b, 'tcx>>(
         &mut self,
+        fx: &FunctionCx<'b, 'tcx, Bx>,
         instance: ty::Instance<'tcx>,
         fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
         args: &[OperandRef<'tcx, &'ll Value>],
         llresult: &'ll Value,
         span: Span,
-        caller_instance: ty::Instance<'tcx>,
     ) {
         let tcx = self.tcx;
         let callee_ty = instance.monomorphic_ty(tcx);
@@ -141,26 +141,17 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
                 self.call(llfn, &[], None)
             }
             "count_code_region" => {
-                if let ty::InstanceDef::Item(fn_def_id) = caller_instance.def {
-                    let caller_fn_path = tcx.def_path_str(fn_def_id);
-                    debug!(
-                        "count_code_region to llvm.instrprof.increment(fn_name={})",
-                        caller_fn_path
-                    );
-
-                    // FIXME(richkadel): (1) Replace raw function name with mangled function name;
-                    // (2) Replace hardcoded `1234` in `hash` with a computed hash (as discussed in)
-                    // the MCP (compiler-team/issues/278); and replace the hardcoded `1` for
-                    // `num_counters` with the actual number of counters per function (when the
-                    // changes are made to inject more than one counter per function).
-                    let (fn_name, _len_val) = self.const_str(Symbol::intern(&caller_fn_path));
+                let coverage_data = fx.mir.coverage_data.as_ref().unwrap();
+                let mangled_fn = tcx.symbol_name(fx.instance);
+                let (mangled_fn_name, _len_val) = self.const_str(mangled_fn.name);
+                let hash = self.const_u64(coverage_data.hash);
                 let index = args[0].immediate();
-                    let hash = self.const_u64(1234);
-                    let num_counters = self.const_u32(1);
-                    self.instrprof_increment(fn_name, hash, num_counters, index)
-                } else {
-                    bug!("intrinsic count_code_region: no src.instance");
-                }
+                let num_counters = self.const_u32(coverage_data.num_counters as u32);
+                debug!(
+                    "count_code_region to LLVM intrinsic instrprof.increment(fn_name={}, hash={:?}, num_counters={:?}, index={:?})",
+                    mangled_fn.name, hash, index, num_counters
+                );
+                self.instrprof_increment(mangled_fn_name, hash, num_counters, index)
             }
             "va_start" => self.va_start(args[0].immediate()),
             "va_end" => self.va_end(args[0].immediate()),

src/librustc_codegen_ssa/mir/block.rs

@@ -688,12 +688,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 .collect();
 
             bx.codegen_intrinsic_call(
+                self,
                 *instance.as_ref().unwrap(),
                 &fn_abi,
                 &args,
                 dest,
                 terminator.source_info.span,
-                self.instance,
             );
 
             if let ReturnDest::IndirectOperand(dst, _) = ret_dest {

src/librustc_codegen_ssa/mir/mod.rs

@@ -21,9 +21,9 @@ use self::operand::{OperandRef, OperandValue};
 
 /// Master context for codegenning from MIR.
 pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
-    instance: Instance<'tcx>,
+    pub instance: Instance<'tcx>,
 
-    mir: &'tcx mir::Body<'tcx>,
+    pub mir: &'tcx mir::Body<'tcx>,
 
     debug_context: Option<FunctionDebugContext<Bx::DIScope>>,
 

src/librustc_codegen_ssa/traits/intrinsic.rs

@@ -1,5 +1,7 @@
 use super::BackendTypes;
 use crate::mir::operand::OperandRef;
+use crate::mir::FunctionCx;
+use crate::traits::BuilderMethods;
 use rustc_middle::ty::{self, Ty};
 use rustc_span::Span;
 use rustc_target::abi::call::FnAbi;
@@ -8,14 +10,14 @@ pub trait IntrinsicCallMethods<'tcx>: BackendTypes {
     /// Remember to add all intrinsics here, in librustc_typeck/check/mod.rs,
     /// and in libcore/intrinsics.rs; if you need access to any llvm intrinsics,
     /// add them to librustc_codegen_llvm/context.rs
-    fn codegen_intrinsic_call(
+    fn codegen_intrinsic_call<'a, Bx: BuilderMethods<'a, 'tcx>>(
         &mut self,
+        fx: &FunctionCx<'a, 'tcx, Bx>,
         instance: ty::Instance<'tcx>,
         fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
         args: &[OperandRef<'tcx, Self::Value>],
         llresult: Self::Value,
         span: Span,
-        caller_instance: ty::Instance<'tcx>,
     );
 
     fn abort(&mut self);

src/librustc_metadata/locator.rs

@@ -488,6 +488,8 @@ impl<'a> CrateLocator<'a> {
                 && self.triple != TargetTriple::from_triple(config::host_triple())
             {
                 err.note(&format!("the `{}` target may not be installed", self.triple));
+            } else if self.crate_name == sym::profiler_builtins {
+                err.note(&"the compiler may have been built without `profiler = true`");
             }
             err.span_label(self.span, "can't find crate");
             err

src/librustc_middle/ich/hcx.rs

@@ -67,13 +67,15 @@ impl<'a> StableHashingContext<'a> {
     /// Don't use it for anything else or you'll run the risk of
     /// leaking data out of the tracking system.
     #[inline]
-    pub fn new(
+    fn new_with_or_without_spans(
         sess: &'a Session,
         krate: &'a hir::Crate<'a>,
         definitions: &'a Definitions,
         cstore: &'a dyn CrateStore,
+        always_ignore_spans: bool,
     ) -> Self {
-        let hash_spans_initial = !sess.opts.debugging_opts.incremental_ignore_spans;
+        let hash_spans_initial =
+            !always_ignore_spans && !sess.opts.debugging_opts.incremental_ignore_spans;
 
         StableHashingContext {
             sess,
@@ -88,6 +90,33 @@ impl<'a> StableHashingContext<'a> {
         }
     }
 
+    #[inline]
+    pub fn new(
+        sess: &'a Session,
+        krate: &'a hir::Crate<'a>,
+        definitions: &'a Definitions,
+        cstore: &'a dyn CrateStore,
+    ) -> Self {
+        Self::new_with_or_without_spans(
+            sess,
+            krate,
+            definitions,
+            cstore,
+            /*always_ignore_spans=*/ false,
+        )
+    }
+
+    #[inline]
+    pub fn ignore_spans(
+        sess: &'a Session,
+        krate: &'a hir::Crate<'a>,
+        definitions: &'a Definitions,
+        cstore: &'a dyn CrateStore,
+    ) -> Self {
+        let always_ignore_spans = true;
+        Self::new_with_or_without_spans(sess, krate, definitions, cstore, always_ignore_spans)
+    }
+
     #[inline]
     pub fn sess(&self) -> &'a Session {
         self.sess

src/librustc_middle/mir/mod.rs

@@ -88,6 +88,19 @@ impl MirPhase {
     }
 }
 
+/// Coverage data computed by the `InstrumentCoverage` MIR pass, when compiling with
+/// `-Zinstrument_coverage`.
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable, TypeFoldable)]
+pub struct CoverageData {
+    /// A hash value that can be used by the consumer of the coverage profile data to detect
+    /// changes to the instrumented source of the associated MIR body (typically, for an
+    /// individual function).
+    pub hash: u64,
+
+    /// The total number of coverage region counters added to this MIR Body.
+    pub num_counters: usize,
+}
+
 /// The lowered representation of a single function.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable, TypeFoldable)]
 pub struct Body<'tcx> {
@@ -164,13 +177,17 @@ pub struct Body<'tcx> {
     /// The user may be writing e.g. `&[(SOME_CELL, 42)][i].1` and this would get promoted, because
     /// we'd statically know that no thing with interior mutability will ever be available to the
     /// user without some serious unsafe code.  Now this means that our promoted is actually
-    /// `&[(SOME_CELL, 42)]` and the MIR using it will do the `&promoted[i].1` projection because the
-    /// index may be a runtime value. Such a promoted value is illegal because it has reachable
+    /// `&[(SOME_CELL, 42)]` and the MIR using it will do the `&promoted[i].1` projection because
+    /// the index may be a runtime value. Such a promoted value is illegal because it has reachable
     /// interior mutability. This flag just makes this situation very obvious where the previous
     /// implementation without the flag hid this situation silently.
     /// FIXME(oli-obk): rewrite the promoted during promotion to eliminate the cell components.
     pub ignore_interior_mut_in_const_validation: bool,
 
+    /// If compiling with `-Zinstrument_coverage`, the `InstrumentCoverage` pass stores summary
+    /// information associated with the MIR, used in code generation of the coverage counters.
+    pub coverage_data: Option<CoverageData>,
+
     predecessor_cache: PredecessorCache,
 }
 
@@ -211,6 +228,7 @@ impl<'tcx> Body<'tcx> {
             required_consts: Vec::new(),
             ignore_interior_mut_in_const_validation: false,
             control_flow_destroyed,
+            coverage_data: None,
             predecessor_cache: PredecessorCache::new(),
         }
     }
@@ -238,6 +256,7 @@ impl<'tcx> Body<'tcx> {
             generator_kind: None,
             var_debug_info: Vec::new(),
             ignore_interior_mut_in_const_validation: false,
+            coverage_data: None,
             predecessor_cache: PredecessorCache::new(),
         }
     }

src/librustc_middle/ty/context.rs

@@ -1284,6 +1284,13 @@ impl<'tcx> TyCtxt<'tcx> {
         StableHashingContext::new(self.sess, krate, self.definitions, &*self.cstore)
     }
 
+    #[inline(always)]
+    pub fn create_no_span_stable_hashing_context(self) -> StableHashingContext<'tcx> {
+        let krate = self.gcx.untracked_crate;
+
+        StableHashingContext::ignore_spans(self.sess, krate, self.definitions, &*self.cstore)
+    }
+
     // This method makes sure that we have a DepNode and a Fingerprint for
     // every upstream crate. It needs to be called once right after the tcx is
     // created.

src/librustc_mir/transform/instrument_coverage.rs

@@ -1,8 +1,15 @@
 use crate::transform::{MirPass, MirSource};
 use crate::util::patch::MirPatch;
+use rustc_data_structures::fingerprint::Fingerprint;
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_hir::lang_items;
+use rustc_hir::*;
+use rustc_middle::ich::StableHashingContext;
 use rustc_middle::mir::interpret::Scalar;
-use rustc_middle::mir::*;
+use rustc_middle::mir::{
+    self, BasicBlock, BasicBlockData, CoverageData, Operand, Place, SourceInfo, StatementKind,
+    Terminator, TerminatorKind, START_BLOCK,
+};
 use rustc_middle::ty;
 use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::DefId;
@@ -12,42 +19,82 @@ use rustc_span::Span;
 /// the intrinsic llvm.instrprof.increment.
 pub struct InstrumentCoverage;
 
+struct Instrumentor<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    num_counters: usize,
+}
+
 impl<'tcx> MirPass<'tcx> for InstrumentCoverage {
-    fn run_pass(&self, tcx: TyCtxt<'tcx>, src: MirSource<'tcx>, body: &mut Body<'tcx>) {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, src: MirSource<'tcx>, mir_body: &mut mir::Body<'tcx>) {
         if tcx.sess.opts.debugging_opts.instrument_coverage {
-            debug!("instrumenting {:?}", src.def_id());
-            instrument_coverage(tcx, body);
+            // If the InstrumentCoverage pass is called on promoted MIRs, skip them.
+            // See: https://github.com/rust-lang/rust/pull/73011#discussion_r438317601
+            if src.promoted.is_none() {
+                assert!(mir_body.coverage_data.is_none());
+
+                let hash = hash_mir_source(tcx, &src);
+
+                debug!(
+                    "instrumenting {:?}, hash: {}, span: {}",
+                    src.def_id(),
+                    hash,
+                    tcx.sess.source_map().span_to_string(mir_body.span)
+                );
+
+                let num_counters = Instrumentor::new(tcx).inject_counters(mir_body);
+
+                mir_body.coverage_data = Some(CoverageData { hash, num_counters });
+            }
         }
     }
 }
 
-// The first counter (start of the function) is index zero.
-const INIT_FUNCTION_COUNTER: u32 = 0;
+impl<'tcx> Instrumentor<'tcx> {
+    fn new(tcx: TyCtxt<'tcx>) -> Self {
+        Self { tcx, num_counters: 0 }
+    }
 
-/// Injects calls to placeholder function `count_code_region()`.
-// FIXME(richkadel): As a first step, counters are only injected at the top of each function.
-// The complete solution will inject counters at each conditional code branch.
-pub fn instrument_coverage<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-    let span = body.span.shrink_to_lo();
+    fn next_counter(&mut self) -> u32 {
+        let next = self.num_counters as u32;
+        self.num_counters += 1;
+        next
+    }
+
+    fn inject_counters(&mut self, mir_body: &mut mir::Body<'tcx>) -> usize {
+        // FIXME(richkadel): As a first step, counters are only injected at the top of each
+        // function. The complete solution will inject counters at each conditional code branch.
+        let top_of_function = START_BLOCK;
+        let entire_function = mir_body.span;
+
+        self.inject_counter(mir_body, top_of_function, entire_function);
+
+        self.num_counters
+    }
+
+    fn inject_counter(
+        &mut self,
+        mir_body: &mut mir::Body<'tcx>,
+        next_block: BasicBlock,
+        code_region: Span,
+    ) {
+        let injection_point = code_region.shrink_to_lo();
 
         let count_code_region_fn = function_handle(
-        tcx,
-        tcx.require_lang_item(lang_items::CountCodeRegionFnLangItem, None),
-        span,
+            self.tcx,
+            self.tcx.require_lang_item(lang_items::CountCodeRegionFnLangItem, None),
+            injection_point,
         );
         let counter_index = Operand::const_from_scalar(
-        tcx,
-        tcx.types.u32,
-        Scalar::from_u32(INIT_FUNCTION_COUNTER),
-        span,
+            self.tcx,
+            self.tcx.types.u32,
+            Scalar::from_u32(self.next_counter()),
+            injection_point,
         );
 
-    let mut patch = MirPatch::new(body);
+        let mut patch = MirPatch::new(mir_body);
 
-    let new_block = patch.new_block(placeholder_block(SourceInfo::outermost(body.span)));
-    let next_block = START_BLOCK;
-
-    let temp = patch.new_temp(tcx.mk_unit(), body.span);
+        let temp = patch.new_temp(self.tcx.mk_unit(), code_region);
+        let new_block = patch.new_block(placeholder_block(code_region));
         patch.patch_terminator(
             new_block,
             TerminatorKind::Call {
@@ -57,19 +104,19 @@ pub fn instrument_coverage<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
                 destination: Some((Place::from(temp), new_block)),
                 cleanup: None,
                 from_hir_call: false,
-            fn_span: span,
+                fn_span: injection_point,
             },
         );
 
         patch.add_statement(new_block.start_location(), StatementKind::StorageLive(temp));
         patch.add_statement(next_block.start_location(), StatementKind::StorageDead(temp));
 
-    patch.apply(body);
+        patch.apply(mir_body);
 
-    // To insert the `new_block` in front of the first block in the counted branch (for example,
-    // the START_BLOCK, at the top of the function), just swap the indexes, leaving the rest of the
-    // graph unchanged.
-    body.basic_blocks_mut().swap(next_block, new_block);
+        // To insert the `new_block` in front of the first block in the counted branch (the
+        // `next_block`), just swap the indexes, leaving the rest of the graph unchanged.
+        mir_body.basic_blocks_mut().swap(next_block, new_block);
+    }
 }
 
 fn function_handle<'tcx>(tcx: TyCtxt<'tcx>, fn_def_id: DefId, span: Span) -> Operand<'tcx> {
@@ -79,14 +126,59 @@ fn function_handle<'tcx>(tcx: TyCtxt<'tcx>, fn_def_id: DefId, span: Span) -> Ope
     Operand::function_handle(tcx, fn_def_id, substs, span)
 }
 
-fn placeholder_block<'tcx>(source_info: SourceInfo) -> BasicBlockData<'tcx> {
+fn placeholder_block(span: Span) -> BasicBlockData<'tcx> {
     BasicBlockData {
         statements: vec![],
         terminator: Some(Terminator {
-            source_info,
+            source_info: SourceInfo::outermost(span),
             // this gets overwritten by the counter Call
             kind: TerminatorKind::Unreachable,
         }),
         is_cleanup: false,
     }
 }
+
+fn hash_mir_source<'tcx>(tcx: TyCtxt<'tcx>, src: &MirSource<'tcx>) -> u64 {
+    let fn_body_id = match tcx.hir().get_if_local(src.def_id()) {
+        Some(node) => match associated_body(node) {
+            Some(body_id) => body_id,
+            _ => bug!("instrumented MirSource does not include a function body: {:?}", node),
+        },
+        None => bug!("instrumented MirSource is not local: {:?}", src),
+    };
+    let hir_body = tcx.hir().body(fn_body_id);
+    let mut hcx = tcx.create_no_span_stable_hashing_context();
+    hash(&mut hcx, &hir_body.value).to_smaller_hash()
+}
+
+fn hash(
+    hcx: &mut StableHashingContext<'tcx>,
+    node: &impl HashStable<StableHashingContext<'tcx>>,
+) -> Fingerprint {
+    let mut stable_hasher = StableHasher::new();
+    node.hash_stable(hcx, &mut stable_hasher);
+    stable_hasher.finish()
+}
+
+fn associated_body<'hir>(node: Node<'hir>) -> Option<BodyId> {
+    match node {
+        Node::Item(Item {
+            kind: ItemKind::Const(_, body) | ItemKind::Static(.., body) | ItemKind::Fn(.., body),
+            ..
+        })
+        | Node::TraitItem(TraitItem {
+            kind:
+                TraitItemKind::Const(_, Some(body)) | TraitItemKind::Fn(_, TraitFn::Provided(body)),
+            ..
+        })
+        | Node::ImplItem(ImplItem {
+            kind: ImplItemKind::Const(_, body) | ImplItemKind::Fn(_, body),
+            ..
+        })
+        | Node::Expr(Expr { kind: ExprKind::Closure(.., body, _, _), .. }) => Some(*body),
+
+        Node::AnonConst(constant) => Some(constant.body),
+
+        _ => None,
+    }
+}

src/librustc_session/options.rs

@@ -877,8 +877,9 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         (such as entering an empty infinite loop) by inserting llvm.sideeffect \
         (default: no)"),
     instrument_coverage: bool = (false, parse_bool, [TRACKED],
-        "instrument the generated code with LLVM code region counters to \
-        (in the future) generate coverage reports (experimental; default: no)"),
+        "instrument the generated code with LLVM code region counters to (in the \
+        future) generate coverage reports (default: no; note, the compiler build \
+        config must include `profiler = true`)"),
     instrument_mcount: bool = (false, parse_bool, [TRACKED],
         "insert function instrument code for mcount-based tracing (default: no)"),
     keep_hygiene_data: bool = (false, parse_bool, [UNTRACKED],

src/librustc_span/symbol.rs

@@ -587,6 +587,7 @@ symbols! {
         proc_macro_mod,
         proc_macro_non_items,
         proc_macro_path_invoc,
+        profiler_builtins,
         profiler_runtime,
         ptr_offset_from,
         pub_restricted,