Subzero: Allow delaying Phi lowering until after register allocation.

tests_lit/llvm2ice_tests/nacl-atomic-cmpxchg-optimization.ll

Index: tests_lit/llvm2ice_tests/nacl-atomic-cmpxchg-optimization.ll
diff --git a/tests_lit/llvm2ice_tests/nacl-atomic-cmpxchg-optimization.ll b/tests_lit/llvm2ice_tests/nacl-atomic-cmpxchg-optimization.ll
index d347dc1d8e3ef5f341ef10c93510a1a35f2ff5ec..258f29489aefeabbed6ea959cdcdc48ac94af021 100644
--- a/tests_lit/llvm2ice_tests/nacl-atomic-cmpxchg-optimization.ll
+++ b/tests_lit/llvm2ice_tests/nacl-atomic-cmpxchg-optimization.ll
@@ -39,11 +39,7 @@ done:
 ; O2-LABEL: test_atomic_cmpxchg_loop
 ; O2: lock
 ; O2-NEXT: cmpxchg dword ptr [e{{[^a].}}], e{{[^a]}}
-; O2-NOT: cmp
-; Make sure the phi assignment for succeeded_first_try is still there.
-; O2: mov {{.*}}, 2
-; O2-NOT: cmp
-; O2: jne
+; O2-NEXT: j{{e|ne}}
 ; Make sure the call isn't accidentally deleted.
 ; O2: call
 ;
@@ -97,8 +93,7 @@ done:
 ; O2-LABEL: test_atomic_cmpxchg_loop_const
 ; O2: lock
 ; O2-NEXT: cmpxchg dword ptr [e{{[^a].}}], e{{[^a]}}
-; O2-NOT: cmp
-; O2: jne
+; O2-NEXT: j{{e|ne}}
 
 ; This is a case where the flags cannot be reused (compare is for some
 ; other condition).
@@ -120,7 +115,6 @@ done:
 ; O2-LABEL: test_atomic_cmpxchg_no_opt
 ; O2: lock
 ; O2-NEXT: cmpxchg dword ptr [e{{[^a].}}], e{{[^a]}}
-; O2: mov {{.*}}
 ; O2: cmp
 ; O2: jle