[dev.ssa] cmd/compile: add simplifying block rewrite rules

Change-Id: Ia946c259628f84dc7031171456563975d2ad5ea9
Reviewed-on: https://go-review.googlesource.com/13381Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -241,8 +241,20 @@
 (If (SETBE cmp) yes no) -> (ULE cmp yes no)
 (If (SETA  cmp) yes no) -> (UGT cmp yes no)
 (If (SETAE cmp) yes no) -> (UGE cmp yes no)
+
 (If cond yes no) -> (NE (TESTB <TypeFlags> cond cond) yes no)
 
+(NE (TESTB (SETL  cmp)) yes no) -> (LT  cmp yes no)
+(NE (TESTB (SETLE cmp)) yes no) -> (LE  cmp yes no)
+(NE (TESTB (SETG  cmp)) yes no) -> (GT  cmp yes no)
+(NE (TESTB (SETGE cmp)) yes no) -> (GE  cmp yes no)
+(NE (TESTB (SETEQ cmp)) yes no) -> (EQ  cmp yes no)
+(NE (TESTB (SETNE cmp)) yes no) -> (NE  cmp yes no)
+(NE (TESTB (SETB  cmp)) yes no) -> (ULT cmp yes no)
+(NE (TESTB (SETBE cmp)) yes no) -> (ULE cmp yes no)
+(NE (TESTB (SETA  cmp)) yes no) -> (UGT cmp yes no)
+(NE (TESTB (SETAE cmp)) yes no) -> (UGE cmp yes no)
+
 (StaticCall [argwid] {target} mem) -> (CALLstatic [argwid] {target} mem)
 (ClosureCall [argwid] entry closure mem) -> (CALLclosure [argwid] entry closure mem)