arm: Stop vadcq, vsbcq intrinsics from overwriting the FPSCR NZ flags

Hi all,

We noticed that calls to the vadcq and vsbcq intrinsics, both of
which use __builtin_arm_set_fpscr_nzcvqc to set the Carry flag in
the FPSCR, would produce the following code:

```
< r2 is the *carry input >
vmrs	r3, FPSCR_nzcvqc
bic	r3, r3, #536870912
orr	r3, r3, r2, lsl #29
vmsr	FPSCR_nzcvqc, r3
```

when the MVE ACLE instead gives a different instruction sequence of:
```
< Rt is the *carry input >
VMRS Rs,FPSCR_nzcvqc
BFI Rs,Rt,#29,#1
VMSR FPSCR_nzcvqc,Rs
```

the bic + orr pair is slower and it's also wrong, because, if the
*carry input is greater than 1, then we risk overwriting the top two
bits of the FPSCR register (the N and Z flags).

This turned out to be a problem in the header file and the solution was
to simply add a `& 1x0u` to the `*carry` input: then the compiler knows
that we only care about the lowest bit and can optimise to a BFI.

Ok for trunk?

Thanks,
Stam Markianos-Wright

gcc/ChangeLog:

	* config/arm/arm_mve.h (__arm_vadcq_s32): Fix arithmetic.
	(__arm_vadcq_u32): Likewise.
	(__arm_vadcq_m_s32): Likewise.
	(__arm_vadcq_m_u32): Likewise.
	(__arm_vsbcq_s32): Likewise.
	(__arm_vsbcq_u32): Likewise.
	(__arm_vsbcq_m_s32): Likewise.
	(__arm_vsbcq_m_u32): Likewise.
	* config/arm/mve.md (get_fpscr_nzcvqc): Make unspec_volatile.

gcc/testsuite/ChangeLog:
	* gcc.target/arm/mve/mve_vadcq_vsbcq_fpscr_overwrite.c: New.

diff --git a/gcc/config/arm/arm_mve.h b/gcc/config/arm/arm_mve.h
index 1774e6eca2b861e2737781e9ada26f3b1d02247d..4ad1c99c28899f60c844a58908ecf21cc117cf8d 100644 (file)
--- a/gcc/config/arm/arm_mve.h
+++ b/gcc/config/arm/arm_mve.h
@@ -4098,7 +4098,7 @@ __extension__ extern __inline int32x4_t
 __attribute__ ((__always_inline__, __gnu_inline__, __artificial__))
 __arm_vadcq_s32 (int32x4_t __a, int32x4_t __b, unsigned * __carry)
 {
-  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | (*__carry << 29));
+  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | ((*__carry & 0x1u) << 29));
   int32x4_t __res = __builtin_mve_vadcq_sv4si (__a, __b);
   *__carry = (__builtin_arm_get_fpscr_nzcvqc () >> 29) & 0x1u;
   return __res;
@@ -4108,7 +4108,7 @@ __extension__ extern __inline uint32x4_t
 __attribute__ ((__always_inline__, __gnu_inline__, __artificial__))
 __arm_vadcq_u32 (uint32x4_t __a, uint32x4_t __b, unsigned * __carry)
 {
-  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | (*__carry << 29));
+  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | ((*__carry & 0x1u) << 29));
   uint32x4_t __res = __builtin_mve_vadcq_uv4si (__a, __b);
   *__carry = (__builtin_arm_get_fpscr_nzcvqc () >> 29) & 0x1u;
   return __res;
@@ -4118,7 +4118,7 @@ __extension__ extern __inline int32x4_t
 __attribute__ ((__always_inline__, __gnu_inline__, __artificial__))
 __arm_vadcq_m_s32 (int32x4_t __inactive, int32x4_t __a, int32x4_t __b, unsigned * __carry, mve_pred16_t __p)
 {
-  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | (*__carry << 29));
+  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | ((*__carry & 0x1u) << 29));
   int32x4_t __res = __builtin_mve_vadcq_m_sv4si (__inactive, __a, __b, __p);
   *__carry = (__builtin_arm_get_fpscr_nzcvqc () >> 29) & 0x1u;
   return __res;
@@ -4128,7 +4128,7 @@ __extension__ extern __inline uint32x4_t
 __attribute__ ((__always_inline__, __gnu_inline__, __artificial__))
 __arm_vadcq_m_u32 (uint32x4_t __inactive, uint32x4_t __a, uint32x4_t __b, unsigned * __carry, mve_pred16_t __p)
 {
-  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | (*__carry << 29));
+  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | ((*__carry & 0x1u) << 29));
   uint32x4_t __res =  __builtin_mve_vadcq_m_uv4si (__inactive, __a, __b, __p);
   *__carry = (__builtin_arm_get_fpscr_nzcvqc () >> 29) & 0x1u;
   return __res;
@@ -4174,7 +4174,7 @@ __extension__ extern __inline int32x4_t
 __attribute__ ((__always_inline__, __gnu_inline__, __artificial__))
 __arm_vsbcq_s32 (int32x4_t __a, int32x4_t __b, unsigned * __carry)
 {
-  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | (*__carry << 29));
+  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | ((*__carry & 0x1u) << 29));
   int32x4_t __res = __builtin_mve_vsbcq_sv4si (__a, __b);
   *__carry = (__builtin_arm_get_fpscr_nzcvqc () >> 29) & 0x1u;
   return __res;
@@ -4184,7 +4184,7 @@ __extension__ extern __inline uint32x4_t
 __attribute__ ((__always_inline__, __gnu_inline__, __artificial__))
 __arm_vsbcq_u32 (uint32x4_t __a, uint32x4_t __b, unsigned * __carry)
 {
-  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | (*__carry << 29));
+  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | ((*__carry & 0x1u) << 29));
   uint32x4_t __res =  __builtin_mve_vsbcq_uv4si (__a, __b);
   *__carry = (__builtin_arm_get_fpscr_nzcvqc () >> 29) & 0x1u;
   return __res;
@@ -4194,7 +4194,7 @@ __extension__ extern __inline int32x4_t
 __attribute__ ((__always_inline__, __gnu_inline__, __artificial__))
 __arm_vsbcq_m_s32 (int32x4_t __inactive, int32x4_t __a, int32x4_t __b, unsigned * __carry, mve_pred16_t __p)
 {
-  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | (*__carry << 29));
+  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | ((*__carry & 0x1u) << 29));
   int32x4_t __res = __builtin_mve_vsbcq_m_sv4si (__inactive, __a, __b, __p);
   *__carry = (__builtin_arm_get_fpscr_nzcvqc () >> 29) & 0x1u;
   return __res;
@@ -4204,7 +4204,7 @@ __extension__ extern __inline uint32x4_t
 __attribute__ ((__always_inline__, __gnu_inline__, __artificial__))
 __arm_vsbcq_m_u32 (uint32x4_t __inactive, uint32x4_t __a, uint32x4_t __b, unsigned * __carry, mve_pred16_t __p)
 {
-  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | (*__carry << 29));
+  __builtin_arm_set_fpscr_nzcvqc((__builtin_arm_get_fpscr_nzcvqc () & ~0x20000000u) | ((*__carry & 0x1u) << 29));
   uint32x4_t __res = __builtin_mve_vsbcq_m_uv4si (__inactive, __a, __b, __p);
   *__carry = (__builtin_arm_get_fpscr_nzcvqc () >> 29) & 0x1u;
   return __res;

diff --git a/gcc/config/arm/mve.md b/gcc/config/arm/mve.md
index 65d8b4b6c4eb7cdf67ebf3ee288809b4a4deae93..9e3570c526438aecba8d9dffbb18879d67cc3d94 100644 (file)
--- a/gcc/config/arm/mve.md
+++ b/gcc/config/arm/mve.md
@@ -6100,7 +6100,7 @@
 
 (define_insn "get_fpscr_nzcvqc"
  [(set (match_operand:SI 0 "register_operand" "=r")
-   (unspec:SI [(reg:SI VFPCC_REGNUM)] UNSPEC_GET_FPSCR_NZCVQC))]
+   (unspec_volatile:SI [(reg:SI VFPCC_REGNUM)] UNSPEC_GET_FPSCR_NZCVQC))]
  "TARGET_HAVE_MVE"
  "vmrs\\t%0, FPSCR_nzcvqc"
   [(set_attr "type" "mve_move")])

diff --git a/gcc/testsuite/gcc.target/arm/mve/mve_vadcq_vsbcq_fpscr_overwrite.c b/gcc/testsuite/gcc.target/arm/mve/mve_vadcq_vsbcq_fpscr_overwrite.c
new file mode 100644 (file)
index 0000000..a8c6cce
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/mve/mve_vadcq_vsbcq_fpscr_overwrite.c
@@ -0,0 +1,67 @@
+/* { dg-do run } */
+/* { dg-require-effective-target arm_mve_hw } */
+/* { dg-options "-O2" } */
+/* { dg-add-options arm_v8_1m_mve } */
+
+#include <arm_mve.h>
+
+volatile int32x4_t c1;
+volatile uint32x4_t c2;
+int *carry;
+
+int
+main ()
+{
+  int32x4_t a1 = vcreateq_s32 (0, 0);
+  int32x4_t b1 = vcreateq_s32 (0, 0);
+  int32x4_t inactive1 = vcreateq_s32 (0, 0);
+
+  uint32x4_t a2 = vcreateq_u32 (0, 0);
+  uint32x4_t b2 = vcreateq_u32 (0, 0);
+  uint32x4_t inactive2 = vcreateq_u32 (0, 0);
+
+  mve_pred16_t p = 0xFFFF;
+  (*carry) = 0xFFFFFFFF;
+
+  __builtin_arm_set_fpscr_nzcvqc (0);
+  c1 = vadcq (a1, b1, carry);
+  if (__builtin_arm_get_fpscr_nzcvqc () & !0x20000000)
+    __builtin_abort ();
+  (*carry) = 0xFFFFFFFF;
+  __builtin_arm_set_fpscr_nzcvqc (0);
+  c2 = vadcq (a2, b2, carry);
+  if (__builtin_arm_get_fpscr_nzcvqc () & !0x20000000)
+    __builtin_abort ();
+  (*carry) = 0xFFFFFFFF;
+  __builtin_arm_set_fpscr_nzcvqc (0);
+  c1 = vsbcq (a1, b1, carry);
+  if (__builtin_arm_get_fpscr_nzcvqc () & !0x20000000)
+    __builtin_abort ();
+  (*carry) = 0xFFFFFFFF;
+  __builtin_arm_set_fpscr_nzcvqc (0);
+  c2 = vsbcq (a2, b2, carry);
+  if (__builtin_arm_get_fpscr_nzcvqc () & !0x20000000)
+    __builtin_abort ();
+  (*carry) = 0xFFFFFFFF;
+  __builtin_arm_set_fpscr_nzcvqc (0);
+  c1 = vadcq_m (inactive1, a1, b1, carry, p);
+  if (__builtin_arm_get_fpscr_nzcvqc () & !0x20000000)
+    __builtin_abort ();
+  (*carry) = 0xFFFFFFFF;
+  __builtin_arm_set_fpscr_nzcvqc (0);
+  c2 = vadcq_m (inactive2, a2, b2, carry, p);
+  if (__builtin_arm_get_fpscr_nzcvqc () & !0x20000000)
+    __builtin_abort ();
+  (*carry) = 0xFFFFFFFF;
+  __builtin_arm_set_fpscr_nzcvqc (0);
+  c1 = vsbcq_m (inactive1, a1, b1, carry, p);
+  if (__builtin_arm_get_fpscr_nzcvqc () & !0x20000000)
+    __builtin_abort ();
+  (*carry) = 0xFFFFFFFF;
+  __builtin_arm_set_fpscr_nzcvqc (0);
+  c2 = vsbcq_m (inactive2, a2, b2, carry, p);
+  if (__builtin_arm_get_fpscr_nzcvqc () & !0x20000000)
+    __builtin_abort ();
+
+  return 0;
+}