Add test case from #216.

The error exposed by this test case no longer happens after the
coalescer was rewritten to to follow the Budimlic paper. It's still a
good coalescer test.

Fixes #216 by including the test case.

cranelift/filetests/regalloc/coalescing-216.cton

@@ -0,0 +1,73 @@
+test regalloc
+set is_64bit
+isa intel haswell
+
+; Reported as https://github.com/stoklund/cretonne/issues/216 from the Binaryen fuzzer.
+;
+; The (old) coalescer creates a virtual register with two identical values.
+function %pr216(i32 [%rdi], i64 vmctx [%rsi]) -> i64 [%rax] native {
+ebb0(v0: i32, v1: i64):
+    v3 = iconst.i64 0
+    v5 = iconst.i32 0
+    brz v5, ebb3(v3)
+    jump ebb4(v3, v3)
+
+ebb4(v11: i64, v29: i64):
+    v6 = iconst.i32 0
+    brz v6, ebb14
+    v9 = iconst.i32 -17
+    v12 = iconst.i32 0xffff_ffff_ffff_8000
+    jump ebb9(v12)
+
+ebb9(v10: i32):
+    brnz v10, ebb8(v9, v11, v11)
+    brz.i32 v9, ebb13
+    v13 = iconst.i32 0
+    brnz v13, ebb6(v11, v11)
+    v14 = iconst.i32 0
+    brz v14, ebb12
+    jump ebb11
+
+ebb12:
+    jump ebb4(v11, v11)
+
+ebb11:
+    jump ebb10(v11)
+
+ebb13:
+    v15 = iconst.i64 1
+    jump ebb10(v15)
+
+ebb10(v21: i64):
+    v16 = iconst.i32 0
+    brnz v16, ebb6(v21, v11)
+    v17 = iconst.i32 0xffff_ffff_ffff_9f35
+    jump ebb8(v17, v21, v11)
+
+ebb8(v8: i32, v23: i64, v28: i64):
+    jump ebb7(v8, v23, v28)
+
+ebb14:
+    v18 = iconst.i32 0
+    jump ebb7(v18, v11, v29)
+
+ebb7(v7: i32, v22: i64, v27: i64):
+    jump ebb6(v22, v27)
+
+ebb6(v20: i64, v25: i64):
+    v19 = iconst.i32 0xffc7
+    brnz v19, ebb4(v20, v25)
+    jump ebb5
+
+ebb5:
+    jump ebb3(v25)
+
+ebb3(v24: i64):
+    jump ebb2(v24)
+
+ebb2(v4: i64):
+    jump ebb1(v4)
+
+ebb1(v2: i64):
+    return v2
+}