diff --git a/cranelift/filetests/parser/instruction_encoding.cton b/cranelift/filetests/parser/instruction_encoding.cton
index c808892701..c9c668dc3f 100644
--- a/cranelift/filetests/parser/instruction_encoding.cton
+++ b/cranelift/filetests/parser/instruction_encoding.cton
@@ -5,7 +5,7 @@ isa riscv
 ; regex: WS=[ \t]*
 
 function %foo(i32, i32) {
-ebb1(v0: i32, v1: i32):
+ebb1(v0: i32 [%x8], v1: i32):
     [-,-] v2 = iadd v0, v1
     [-] trap
     [R#1234, %x5, %x11] v6, v7 = iadd_cout v2, v0
@@ -14,7 +14,7 @@ ebb1(v0: i32, v1: i32):
     [Iret#5] return v0, v8
 }
 ; sameln: function %foo(i32, i32) native {
-; nextln: $ebb1($v0: i32, $v1: i32):
+; nextln: $ebb1($v0: i32 [%x8], $v1: i32):
 ; nextln:     [-,-]$WS $v2 = iadd $v0, $v1
 ; nextln:     [-]$WS trap
 ; nextln:     [R#1234,%x5,%x11]$WS $v6, $v7 = iadd_cout $v2, $v0
diff --git a/cranelift/filetests/regalloc/coalesce.cton b/cranelift/filetests/regalloc/coalesce.cton
index 80cd38e62e..7624eaef7c 100644
--- a/cranelift/filetests/regalloc/coalesce.cton
+++ b/cranelift/filetests/regalloc/coalesce.cton
@@ -4,6 +4,7 @@ isa riscv
 ; Test the coalescer.
 ; regex: V=v\d+
 ; regex: WS=\s+
+; regex: LOC=%\w+
 
 ; This function is already CSSA, so no copies should be inserted.
 function %cssa(i32) -> i32 {
@@ -81,7 +82,7 @@ ebb0(v0: i32):
 
 ebb1(v10: i32, v11: i32):
     ; v11 needs to be isolated because it interferes with v10.
-    ; check: $ebb1($v10: i32, $(nv11a=$V): i32)
+    ; check: $ebb1($v10: i32 [$LOC], $(nv11a=$V): i32 [$LOC])
     ; check: $v11 = copy $nv11a
     v12 = iadd v10, v11
     v13 = icmp ult v12, v0
diff --git a/cranelift/filetests/regalloc/spill.cton b/cranelift/filetests/regalloc/spill.cton
index 901509a8d4..8f00c93184 100644
--- a/cranelift/filetests/regalloc/spill.cton
+++ b/cranelift/filetests/regalloc/spill.cton
@@ -25,7 +25,7 @@ function %pyramid(i32) -> i32 {
 ; check: ss2 = spill_slot 4
 ; not: spill_slot
 ebb0(v1: i32):
-; check: $ebb0($(rv1=$V): i32, $(rlink=$V): i32)
+; check: $ebb0($(rv1=$V): i32 [%x10], $(rlink=$V): i32 [%x1])
     ; check: ,ss0]$WS $v1 = spill $rv1
     ; nextln: ,ss1]$WS $(link=$V) = spill $rlink
     ; not: spill
@@ -155,7 +155,7 @@ function %use_spilled_value(i32) -> i32 {
 ; check: ss1 = spill_slot 4
 ; check: ss2 = spill_slot 4
 ebb0(v1: i32):
-; check: $ebb0($(rv1=$V): i32, $(rlink=$V): i32)
+; check: $ebb0($(rv1=$V): i32 [%x10], $(rlink=$V): i32 [%x1])
     ; check: ,ss0]$WS $v1 = spill $rv1
     ; nextln: ,ss1]$WS $(link=$V) = spill $rlink
     ; not: spill
diff --git a/lib/cretonne/src/ir/valueloc.rs b/lib/cretonne/src/ir/valueloc.rs
index a6a358e14b..1e3cf20f87 100644
--- a/lib/cretonne/src/ir/valueloc.rs
+++ b/lib/cretonne/src/ir/valueloc.rs
@@ -25,6 +25,14 @@ impl Default for ValueLoc {
 }
 
 impl ValueLoc {
+    /// Is this an assigned location? (That is, not `Unassigned`).
+    pub fn is_assigned(&self) -> bool {
+        match *self {
+            ValueLoc::Unassigned => false,
+            _ => true,
+        }
+    }
+
     /// Get the register unit of this location, or panic.
     pub fn unwrap_reg(self) -> RegUnit {
         match self {
diff --git a/lib/cretonne/src/write.rs b/lib/cretonne/src/write.rs
index 77f0209da3..3467f79adb 100644
--- a/lib/cretonne/src/write.rs
+++ b/lib/cretonne/src/write.rs
@@ -91,11 +91,22 @@ fn write_preamble(
 //
 // ====--------------------------------------------------------------------------------------====//
 
-pub fn write_arg(w: &mut Write, func: &Function, arg: Value) -> Result {
-    write!(w, "{}: {}", arg, func.dfg.value_type(arg))
+pub fn write_arg(w: &mut Write, func: &Function, regs: Option<&RegInfo>, arg: Value) -> Result {
+    write!(w, "{}: {}", arg, func.dfg.value_type(arg))?;
+    let loc = func.locations[arg];
+    if loc.is_assigned() {
+        write!(w, " [{}]", loc.display(regs))?
+    }
+
+    Ok(())
 }
 
-pub fn write_ebb_header(w: &mut Write, func: &Function, ebb: Ebb) -> Result {
+pub fn write_ebb_header(
+    w: &mut Write,
+    func: &Function,
+    isa: Option<&TargetIsa>,
+    ebb: Ebb,
+) -> Result {
     // Write out the basic block header, outdented:
     //
     //    ebb1:
@@ -108,24 +119,27 @@ pub fn write_ebb_header(w: &mut Write, func: &Function, ebb: Ebb) -> Result {
         write!(w, "                    ")?;
     }
 
+    let regs = isa.map(TargetIsa::register_info);
+    let regs = regs.as_ref();
+
     let mut args = func.dfg.ebb_args(ebb).iter().cloned();
     match args.next() {
         None => return writeln!(w, "{}:", ebb),
         Some(arg) => {
             write!(w, "{}(", ebb)?;
-            write_arg(w, func, arg)?;
+            write_arg(w, func, regs, arg)?;
         }
     }
     // Remaining arguments.
     for arg in args {
         write!(w, ", ")?;
-        write_arg(w, func, arg)?;
+        write_arg(w, func, regs, arg)?;
     }
     writeln!(w, "):")
 }
 
 pub fn write_ebb(w: &mut Write, func: &Function, isa: Option<&TargetIsa>, ebb: Ebb) -> Result {
-    write_ebb_header(w, func, ebb)?;
+    write_ebb_header(w, func, isa, ebb)?;
     for inst in func.layout.ebb_insts(ebb) {
         write_instruction(w, func, isa, inst)?;
     }
diff --git a/lib/reader/src/parser.rs b/lib/reader/src/parser.rs
index e5c59530fc..f9b3f334e1 100644
--- a/lib/reader/src/parser.rs
+++ b/lib/reader/src/parser.rs
@@ -1449,22 +1449,35 @@ impl<'a> Parser<'a> {
 
     // Parse a single EBB argument declaration, and append it to `ebb`.
     //
-    // ebb-arg ::= * Value(v) ":" Type(t)
+    // ebb-arg ::= * Value(v) ":" Type(t) arg-loc?
+    // arg-loc ::= "[" value-location "]"
     //
     fn parse_ebb_arg(&mut self, ctx: &mut Context, ebb: Ebb) -> Result<()> {
-        // ebb-arg ::= * Value(v) ":" Type(t)
+        // ebb-arg ::= * Value(v) ":" Type(t) arg-loc?
         let v = self.match_value("EBB argument must be a value")?;
         let v_location = self.loc;
-        // ebb-arg ::= Value(v) * ":" Type(t)
+        // ebb-arg ::= Value(v) * ":" Type(t) arg-loc?
         self.match_token(
             Token::Colon,
             "expected ':' after EBB argument",
         )?;
-        // ebb-arg ::= Value(v) ":" * Type(t)
+        // ebb-arg ::= Value(v) ":" * Type(t) arg-loc?
         let t = self.match_type("expected EBB argument type")?;
         // Allocate the EBB argument and add the mapping.
         let value = ctx.function.dfg.append_ebb_arg(ebb, t);
-        ctx.map.def_value(v, value, &v_location)
+        ctx.map.def_value(v, value, &v_location)?;
+
+        // ebb-arg ::= Value(v) ":" Type(t) * arg-loc?
+        if self.optional(Token::LBracket) {
+            let loc = self.parse_value_location(ctx)?;
+            ctx.function.locations[value] = loc;
+            self.match_token(
+                Token::RBracket,
+                "expected ']' after value location",
+            )?;
+        }
+
+        Ok(())
     }
 
     fn parse_value_location(&mut self, ctx: &Context) -> Result<ValueLoc> {