CmmCommonBlockElim: Ignore CmmUnwind nodes

We don't want unwind information to affect the code we produce.
Consequently we need to ensure that CBE ignores unwind nodes for the
purposes of equality.

Test Plan: Validate

Reviewers: scpmw, simonmar, austin

Reviewed By: simonmar

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2739

compiler/cmm/CmmCommonBlockElim.hs

@@ -134,7 +134,6 @@ hash_block block =
 
         hash_node :: CmmNode O x -> Word32
         hash_node n | dont_care n = 0 -- don't care
-        hash_node (CmmUnwind _ e) = hash_e e
         hash_node (CmmAssign r e) = hash_reg r + hash_e e
         hash_node (CmmStore e e') = hash_e e + hash_e e'
         hash_node (CmmUnsafeForeignCall t _ as) = hash_tgt t + hash_list hash_e as
@@ -181,6 +180,7 @@ hash_block block =
 dont_care :: CmmNode O x -> Bool
 dont_care CmmComment {}  = True
 dont_care CmmTick {}     = True
+dont_care CmmUnwind {}   = True
 dont_care _other         = False
 
 -- Utilities: equality and substitution on the graph.