[PATCH][ARM][gcc-7] Fix wrong code by arm_final_prescan with fp16 move instructions

[Sudakshina Das]

Hi

This patch is the fix for gcc-7 for the same issue as mentioned in:
https://gcc.gnu.org/ml/gcc-patches/2017-11/msg02209.html

For the following test case:
__fp16
test_select (__fp16 a, __fp16 b, __fp16 c)
{
  return (a < b) ? b : c;
}

when compiled with -O2 -mfpu=fp-armv8 -march=armv8.2-a+fp16 -marm 
-mfloat-abi=hard generates wrong code:

test_select:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        vcvtb.f32.f16   s0, s0
        vcvtb.f32.f16   s15, s1
        vmov.f16        r3, s2  @ __fp16
        vcmpe.f32       s0, s15
        vmrs    APSR_nzcv, FPSCR
        // <------ No conditional branch
        vmov.f16        r3, s1  @ __fp16
.L1:
        vmov.f16        s0, r3  @ __fp16
        bx      lr

There should have been a conditional branch there to skip one of the VMOVs.
This patch fixes this problem by making *movhf_vfp_fp16 unconditional.

Testing done: Add a new test case and checked for regressions on 
bootstrapped arm-none-linux-gnueabihf.

Is this ok for gcc-7?

Sudi

ChangeLog entry are as follow:

*** gcc/ChangeLog ***

2017-11-30  Sudakshina Das  <sudi....@arm.com>

        * config/arm/vfp.md (*movhf_vfp_fp16): Add conds attribute.

*** gcc/testsuite/ChangeLog ***

2017-11-30  Sudakshina Das  <sudi....@arm.com>

        * gcc.target/arm/armv8_2-fp16-move-2.c: New test.
diff --git a/gcc/config/arm/vfp.md b/gcc/config/arm/vfp.md
index d8f77e2ffe4fdb7c952d6a5ac947d91f89ce259d..9f06c3da9526d09e43836a60f14da9a49671a393 100644
--- a/gcc/config/arm/vfp.md
+++ b/gcc/config/arm/vfp.md
@@ -456,7 +456,10 @@
       gcc_unreachable ();
     }
  }
-  [(set_attr "predicable" "yes, yes, no, yes, no, no, no, no, no, no")
+  [(set_attr "conds" "*, *, unconditional, *, unconditional, unconditional,\
+		      unconditional, unconditional, unconditional,\
+		      unconditional")
+   (set_attr "predicable" "yes, yes, no, yes, no, no, no, no, no, no")
    (set_attr "predicable_short_it" "no, no, no, yes,\
 				    no, no, no, no,\
 				    no, no")
diff --git a/gcc/testsuite/gcc.target/arm/armv8_2-fp16-move-2.c b/gcc/testsuite/gcc.target/arm/armv8_2-fp16-move-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..ac7d4e3f2a9fb1d70a9ce95062dc6db4a69272ff
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/armv8_2-fp16-move-2.c
@@ -0,0 +1,11 @@
+/* { dg-do compile }  */
+/* { dg-require-effective-target arm_v8_2a_fp16_scalar_ok }  */
+/* { dg-options "-O2 -mfpu=fp-armv8 -march=armv8.2-a+fp16 -marm -mfloat-abi=hard" }  */
+/* { dg-add-options arm_v8_2a_fp16_scalar }  */
+
+__fp16
+test_select (__fp16 a, __fp16 b, __fp16 c)
+{
+  return (a < b) ? b : c;
+}
+/* { dg-final { scan-assembler "bpl" } } */