This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
[PATCH][ARM] Fix wrong code by arm_final_prescan with fp16 move instructions
- From: Sudakshina Das <sudi dot das at arm dot com>
- To: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Cc: nd <nd at arm dot com>, kyrylo dot tkachov at arm dot com, Ramana Radhakrishnan <Ramana dot Radhakrishnan at arm dot com>, Richard Earnshaw <Richard dot Earnshaw at arm dot com>
- Date: Fri, 24 Nov 2017 14:57:50 +0000
- Subject: [PATCH][ARM] Fix wrong code by arm_final_prescan with fp16 move instructions
- Authentication-results: sourceware.org; auth=none
- Authentication-results: spf=none (sender IP is ) smtp.mailfrom=Sudi dot Das at arm dot com;
- Nodisclaimer: True
- Spamdiagnosticmetadata: NSPM
- Spamdiagnosticoutput: 1:99
Hi
For the following test case:
__fp16
test_select (__fp16 a, __fp16 b, __fp16 c)
{
return (a < b) ? b : c;
}
when compiled with -mfpu=fp-armv8 -march=armv8.2-a+fp16 -marm
-mfloat-abi=hard trunk 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
vcmpe.f32 s0, s15
vmrs APSR_nzcv, FPSCR
// <------ No conditional branch!
vmov s1, s2 @ __fp16
.L2:
vmov s0, s1 @ __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
wherever needed.
Testing done: Add a new test case and checked for regressions
arm-none-linux-gnueabihf.
Is this ok for trunk?
Sudi
ChangeLog entry are as follow:
*** gcc/ChangeLog ***
2017-11-24 Sudakshina Das <sudi.das@arm.com>
* config/arm/vfp.md (*movhf_vfp_fp16): Add conds attribute.
*** gcc/testsuite/ChangeLog ***
2017-11-24 Sudakshina Das <sudi.das@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 075a938..61b6477 100644
--- a/gcc/config/arm/vfp.md
+++ b/gcc/config/arm/vfp.md
@@ -410,7 +410,10 @@
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 0000000..fcb857f
--- /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 -marm" } */
+/* { 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 "bmi" } } */