arm: Adjust cost of vector of constant zero

Neon vector comparisons have a dedicated version when comparing with
constant zero: it means its cost is free.

Adjust the cost in arm_rtx_costs_internal accordingly, for Neon only,
since MVE does not support this.

2021-01-28  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	PR target/98730
	* config/arm/arm.c (arm_rtx_costs_internal): Adjust cost of vector
	of constant zero for comparisons.

	gcc/testsuite/
	PR target/98730
	* gcc.target/arm/simd/vceqzq_p64.c: Update expected result.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index bebccc1..e22396d 100644 (file)
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -11211,11 +11211,23 @@ arm_rtx_costs_internal (rtx x, enum rtx_code code, enum rtx_code outer_code,
       return true;
 
     case EQ:
-    case NE:
-    case LT:
-    case LE:
-    case GT:
     case GE:
+    case GT:
+    case LE:
+    case LT:
+      /* Neon has special instructions when comparing with 0 (vceq, vcge, vcgt,
+        vcle and vclt). */
+      if (TARGET_NEON
+         && TARGET_HARD_FLOAT
+         && (VALID_NEON_DREG_MODE (mode) || VALID_NEON_QREG_MODE (mode))
+         && (XEXP (x, 1) == CONST0_RTX (mode)))
+       {
+         *cost = 0;
+         return true;
+       }
+
+      /* Fall through.  */
+    case NE:
     case LTU:
     case LEU:
     case GEU:

diff --git a/gcc/testsuite/gcc.target/arm/simd/vceqzq_p64.c b/gcc/testsuite/gcc.target/arm/simd/vceqzq_p64.c
index 640754c..a99bb8a 100644 (file)
--- a/gcc/testsuite/gcc.target/arm/simd/vceqzq_p64.c
+++ b/gcc/testsuite/gcc.target/arm/simd/vceqzq_p64.c
@@ -15,4 +15,4 @@ void func()
   result2 = vceqzq_p64 (v2);
 }
 
-/* { dg-final { scan-assembler-times "vceq\.i32\[ \t\]+\[dD\]\[0-9\]+, ?\[dD\]\[0-9\]+, ?\[dD\]\[0-9\]+\n" 2 } } */
+/* { dg-final { scan-assembler-times "vceq\.i32\[ \t\]+\[dD\]\[0-9\]+, ?\[dD\]\[0-9\]+, #0\n" 2 } } */