[Bug rtl-optimization/87871] [9 Regression] testcases fail after r265398 on arm

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87871

--- Comment #44 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Well, it requires that the RA looks specially for this kind of pattern and if
it ends up being a noop move, nothing simplifies the pattern again back to
normal comparison, and as Segher noted, it can negatively affect other
optimization passes.

Completely untested patch peephole2 patch:
--- gcc/config/arm/arm.md.jj    2019-03-19 11:04:49.283170205 +0100
+++ gcc/config/arm/arm.md       2019-04-18 16:21:18.974543408 +0200
@@ -10928,12 +10928,22 @@
   [(set (match_operand:SI 0 "arm_general_register_operand" "")
        (match_operand:SI 1 "arm_general_register_operand" ""))
    (set (reg:CC CC_REGNUM)
-       (compare:CC (match_dup 1) (const_int 0)))]
+       (compare:CC (match_operand:SI 2 "arm_general_register_operand" "")
+                   (const_int 0)))]
+  "TARGET_ARM
+   && (rtx_equal_p (operands[2], operands[0])
+       || rtx_equal_p (operands[2], operands[1]))"
+  [(parallel [(set (reg:CC CC_REGNUM) (compare:CC (match_dup 1) (const_int
0)))
+             (set (match_dup 0) (match_dup 1))])])
+
+(define_peephole2
+  [(set (reg:CC CC_REGNUM)
+       (compare:CC (match_operand:SI 1 "arm_general_register_operand" "")
+                   (const_int 0)))]
+   (set (match_operand:SI 0 "arm_general_register_operand" "") (match_dup 1))]
   "TARGET_ARM"
   [(parallel [(set (reg:CC CC_REGNUM) (compare:CC (match_dup 1) (const_int
0)))
-             (set (match_dup 0) (match_dup 1))])]
-  ""
-)
+             (set (match_dup 0) (match_dup 1))])])

 (define_split
   [(set (match_operand:SI 0 "s_register_operand" "")