diff --git a/cranelift/src/libreader/lib.rs b/cranelift/src/libreader/lib.rs
index 94436e12f1..79f9b23521 100644
--- a/cranelift/src/libreader/lib.rs
+++ b/cranelift/src/libreader/lib.rs
@@ -8,8 +8,10 @@ extern crate cretonne;
 pub use parser::{Result, parse_functions, parse_test};
 pub use testcommand::{TestCommand, TestOption};
 pub use testfile::{TestFile, Details};
+pub use sourcemap::SourceMap;
 
 mod lexer;
 mod parser;
 mod testcommand;
 mod testfile;
+mod sourcemap;
diff --git a/cranelift/src/libreader/parser.rs b/cranelift/src/libreader/parser.rs
index 63a635b3f7..54a53310ee 100644
--- a/cranelift/src/libreader/parser.rs
+++ b/cranelift/src/libreader/parser.rs
@@ -21,6 +21,7 @@ use cretonne::ir::instructions::{InstructionFormat, InstructionData, VariableArg
                                  BranchData, ReturnData};
 use testfile::{TestFile, Details, Comment};
 use testcommand::TestCommand;
+use sourcemap;
 
 pub use lexer::Location;
 
@@ -539,11 +540,16 @@ impl<'a> Parser<'a> {
         self.token();
         self.comment_entity = None;
 
-        // Rewrite references to values and EBBs after parsing everuthing to allow forward
+        // Rewrite references to values and EBBs after parsing everything to allow forward
         // references.
         try!(ctx.rewrite_references());
 
-        Ok((ctx.function, Details { comments: mem::replace(&mut self.comments, Vec::new()) }))
+        let details = Details {
+            comments: mem::replace(&mut self.comments, Vec::new()),
+            map: sourcemap::new(ctx.values, ctx.ebbs, ctx.stack_slots, ctx.jump_tables),
+        };
+
+        Ok((ctx.function, details))
     }
 
     // Parse a function spec.
@@ -1307,7 +1313,7 @@ mod tests {
 
     #[test]
     fn comments() {
-        let (func, Details { comments }) =
+        let (func, Details { comments, .. }) =
             Parser::new("; before
                          function comment() { ; decl
                             ss10  = stack_slot 13 ; stackslot.
diff --git a/cranelift/src/libreader/sourcemap.rs b/cranelift/src/libreader/sourcemap.rs
new file mode 100644
index 0000000000..9a601a3e39
--- /dev/null
+++ b/cranelift/src/libreader/sourcemap.rs
@@ -0,0 +1,133 @@
+//! Source map for translating source entity names to parsed entities.
+//!
+//! When the parser reads in a source file, entities like instructions, EBBs, and values get new
+//! entity numbers. The parser maintains a mapping from the entity names in the source to the final
+//! entity references.
+//!
+//! The `SourceMap` struct defined in this module makes the same mapping available to parser
+//! clients.
+
+use std::collections::HashMap;
+use cretonne::ir::{StackSlot, JumpTable, Ebb, Value};
+use cretonne::ir::entities::AnyEntity;
+
+/// Mapping from source entity names to entity references that are valid in the parsed function.
+#[derive(Debug)]
+pub struct SourceMap {
+    values: HashMap<Value, Value>, // vNN, vxNN
+    ebbs: HashMap<Ebb, Ebb>, // ebbNN
+    stack_slots: HashMap<u32, StackSlot>, // ssNN
+    jump_tables: HashMap<u32, JumpTable>, // jtNN
+}
+
+/// Read-only interface which is exposed outside the parser crate.
+impl SourceMap {
+    /// Look up an entity by source name.
+    /// Returns the entity reference corresponding to `name`, if it exists.
+    pub fn lookup_str(&self, name: &str) -> Option<AnyEntity> {
+        split_entity_name(name).and_then(|(ent, num)| {
+            match ent {
+                "v" => {
+                    Value::direct_with_number(num)
+                        .and_then(|v| self.values.get(&v).cloned())
+                        .map(AnyEntity::Value)
+                }
+                "vx" => {
+                    Value::table_with_number(num)
+                        .and_then(|v| self.values.get(&v).cloned())
+                        .map(AnyEntity::Value)
+                }
+                "ebb" => {
+                    Ebb::with_number(num)
+                        .and_then(|e| self.ebbs.get(&e).cloned())
+                        .map(AnyEntity::Ebb)
+                }
+                "ss" => self.stack_slots.get(&num).cloned().map(AnyEntity::StackSlot),
+                "jt" => self.jump_tables.get(&num).cloned().map(AnyEntity::JumpTable),
+                _ => None,
+            }
+        })
+    }
+}
+
+/// Get the number of decimal digits at the end of `s`.
+fn trailing_digits(s: &str) -> usize {
+    // It's faster to iterate backwards over bytes, and we're only counting ASCII digits.
+    s.as_bytes().iter().rev().cloned().take_while(|&b| b'0' <= b && b <= b'9').count()
+}
+
+/// Pre-parse a supposed entity name by splitting it into two parts: A head of lowercase ASCII
+/// letters and numeric tail.
+fn split_entity_name(name: &str) -> Option<(&str, u32)> {
+    let (head, tail) = name.split_at(name.len() - trailing_digits(name));
+    if tail.len() > 1 && tail.starts_with('0') {
+        None
+    } else {
+        tail.parse().ok().map(|n| (head, n))
+    }
+}
+
+/// Create a new SourceMap from all the individual mappings.
+pub fn new(values: HashMap<Value, Value>,
+           ebbs: HashMap<Ebb, Ebb>,
+           stack_slots: HashMap<u32, StackSlot>,
+           jump_tables: HashMap<u32, JumpTable>)
+           -> SourceMap {
+    SourceMap {
+        values: values,
+        ebbs: ebbs,
+        stack_slots: stack_slots,
+        jump_tables: jump_tables,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{trailing_digits, split_entity_name};
+    use parse_test;
+
+    #[test]
+    fn digits() {
+        assert_eq!(trailing_digits(""), 0);
+        assert_eq!(trailing_digits("x"), 0);
+        assert_eq!(trailing_digits("0x"), 0);
+        assert_eq!(trailing_digits("x1"), 1);
+        assert_eq!(trailing_digits("1x1"), 1);
+        assert_eq!(trailing_digits("1x01"), 2);
+    }
+
+    #[test]
+    fn entity_name() {
+        assert_eq!(split_entity_name(""), None);
+        assert_eq!(split_entity_name("x"), None);
+        assert_eq!(split_entity_name("x+"), None);
+        assert_eq!(split_entity_name("x+1"), Some(("x+", 1)));
+        assert_eq!(split_entity_name("x-1"), Some(("x-", 1)));
+        assert_eq!(split_entity_name("1"), Some(("", 1)));
+        assert_eq!(split_entity_name("x1"), Some(("x", 1)));
+        assert_eq!(split_entity_name("xy0"), Some(("xy", 0)));
+        // Reject this non-canonical form.
+        assert_eq!(split_entity_name("inst01"), None);
+    }
+
+    #[test]
+    fn details() {
+        let tf = parse_test("function detail() {
+                               ss10 = stack_slot 13
+                               jt10 = jump_table ebb0
+                             ebb0(v4: i32, vx7: i32):
+                               v10 = iadd v4, vx7
+                             }")
+            .unwrap();
+        let map = &tf.functions[0].1.map;
+
+        assert_eq!(map.lookup_str("v0"), None);
+        assert_eq!(map.lookup_str("ss1"), None);
+        assert_eq!(map.lookup_str("ss10").unwrap().to_string(), "ss0");
+        assert_eq!(map.lookup_str("jt10").unwrap().to_string(), "jt0");
+        assert_eq!(map.lookup_str("ebb0").unwrap().to_string(), "ebb0");
+        assert_eq!(map.lookup_str("v4").unwrap().to_string(), "vx0");
+        assert_eq!(map.lookup_str("vx7").unwrap().to_string(), "vx1");
+        assert_eq!(map.lookup_str("v10").unwrap().to_string(), "v0");
+    }
+}
diff --git a/cranelift/src/libreader/testfile.rs b/cranelift/src/libreader/testfile.rs
index 3b4f3d4e16..34cfabce83 100644
--- a/cranelift/src/libreader/testfile.rs
+++ b/cranelift/src/libreader/testfile.rs
@@ -7,6 +7,7 @@
 use cretonne::ir::Function;
 use cretonne::ir::entities::AnyEntity;
 use testcommand::TestCommand;
+use sourcemap::SourceMap;
 
 /// A parsed test case.
 ///
@@ -24,6 +25,7 @@ pub struct TestFile<'a> {
 #[derive(Debug)]
 pub struct Details<'a> {
     pub comments: Vec<Comment<'a>>,
+    pub map: SourceMap,
 }
 
 /// A comment in a parsed function.