Append link and sret arguments in legalize_signature.

These special-purpose arguments and return values are only relevant for
the function being compiled, so add a `current` flag to
legalize_signature().

- Add the necessary argument values to the entry block to represent
  the special-purpose arguments.
- Propagate the link and sret arguments to return instructions if the
  legalized signature asks for it.

cranelift/filetests/isa/riscv/legalize-abi.cton

@@ -6,11 +6,11 @@ isa riscv
 
 function int_split_args(i64) -> i64 {
 ebb0(v0: i64):
-    ; check: $ebb0($(v0l=$V): i32, $(v0h=$V): i32):
+    ; check: $ebb0($(v0l=$V): i32, $(v0h=$V): i32, $(link=$V): i32):
     ; check: $v0 = iconcat $v0l, $v0h
     v1 = iadd_imm v0, 1
     ; check: $(v1l=$V), $(v1h=$V) = isplit $v1
-    ; check: return $v1l, $v1h
+    ; check: return $v1l, $v1h, $link
     return v1
 }
 
@@ -31,7 +31,7 @@ function split_ret_val() {
     fn1 = function foo() -> i64
 ebb0:
     v1 = call fn1()
-    ; check: $ebb0:
+    ; check: $ebb0($(link=$V): i32):
     ; nextln: $(v1l=$V), $(v1h=$V) = call $fn1()
     ; check: $v1 = iconcat $v1l, $v1h
     jump ebb1(v1)
@@ -46,7 +46,7 @@ function split_ret_val2() {
     fn1 = function foo() -> i32, i64
 ebb0:
     v1, v2 = call fn1()
-    ; check: $ebb0:
+    ; check: $ebb0($(link=$V): i32):
     ; nextln: $v1, $(v2l=$V), $(v2h=$V) = call $fn1()
     ; check: $v2 = iconcat $v2l, $v2h
     jump ebb1(v1, v2)
@@ -58,11 +58,11 @@ ebb1(v9: i32, v10: i64):
 
 function int_ext(i8, i8 sext, i8 uext) -> i8 uext {
 ebb0(v1: i8, v2: i8, v3: i8):
-    ; check: $ebb0($v1: i8, $(v2x=$V): i32, $(v3x=$V): i32):
+    ; check: $ebb0($v1: i8, $(v2x=$V): i32, $(v3x=$V): i32, $(link=$V): i32):
     ; check: $v2 = ireduce.i8 $v2x
     ; check: $v3 = ireduce.i8 $v3x
     ; check: $(v1x=$V) = uextend.i32 $v1
-    ; check: return $v1x
+    ; check: return $v1x, $link
     return v1
 }
 
@@ -71,7 +71,7 @@ function ext_ret_val() {
     fn1 = function foo() -> i8 sext
 ebb0:
     v1 = call fn1()
-    ; check: $ebb0:
+    ; check: $ebb0($V: i32):
     ; nextln: $(rv=$V) = call $fn1()
     ; check: $v1 = ireduce.i8 $rv
     jump ebb1(v1)
@@ -83,7 +83,7 @@ ebb1(v10: i8):
 
 function vector_split_args(i64x4) -> i64x4 {
 ebb0(v0: i64x4):
-    ; check: $ebb0($(v0al=$V): i32, $(v0ah=$V): i32, $(v0bl=$V): i32, $(v0bh=$V): i32, $(v0cl=$V): i32, $(v0ch=$V): i32, $(v0dl=$V): i32, $(v0dh=$V): i32):
+    ; check: $ebb0($(v0al=$V): i32, $(v0ah=$V): i32, $(v0bl=$V): i32, $(v0bh=$V): i32, $(v0cl=$V): i32, $(v0ch=$V): i32, $(v0dl=$V): i32, $(v0dh=$V): i32, $(link=$V): i32):
     ; check: $(v0a=$V) = iconcat $v0al, $v0ah
     ; check: $(v0b=$V) = iconcat $v0bl, $v0bh
     ; check: $(v0ab=$V) = vconcat $v0a, $v0b
@@ -99,7 +99,7 @@ ebb0(v0: i64x4):
     ; check: $(v1c=$V), $(v1d=$V) = vsplit $v1cd
     ; check: $(v1cl=$V), $(v1ch=$V) = isplit $v1c
     ; check: $(v1dl=$V), $(v1dh=$V) = isplit $v1d
-    ; check: return $v1al, $v1ah, $v1bl, $v1bh, $v1cl, $v1ch, $v1dl, $v1dh
+    ; check: return $v1al, $v1ah, $v1bl, $v1bh, $v1cl, $v1ch, $v1dl, $v1dh, $link
     return v1
 }