This patch adds new function libc_feholdsetround_noex_aarch64_ctx, enabling

further optimization. libc_feholdsetround_aarch64_ctx now only needs to
read the FPCR in the typical case, avoiding a redundant FPSR read.
Performance results show a good improvement (5-10% on sin()) on cores with
expensive FPCR/FPSR instructions.

diff --git a/ChangeLog b/ChangeLog
index f1c965e..1702300 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2014-08-07  Wilco Dijkstra  <wdijkstr@arm.com>
 
+       * sysdeps/aarch64/fpu/math_private.h
+       (libc_feholdsetround_noex_aarch64_ctx): New function.
+
+2014-08-07  Wilco Dijkstra  <wdijkstr@arm.com>
+
        * sysdeps/arm/armv6/strcpy.S (strcpy):
        Fix performance issue in misaligned cases.
 

diff --git a/sysdeps/aarch64/fpu/math_private.h b/sysdeps/aarch64/fpu/math_private.h
index 023c9d0..b13c030 100644 (file)
--- a/sysdeps/aarch64/fpu/math_private.h
+++ b/sysdeps/aarch64/fpu/math_private.h
@@ -228,12 +228,9 @@ static __always_inline void
 libc_feholdsetround_aarch64_ctx (struct rm_ctx *ctx, int r)
 {
   fpu_control_t fpcr;
-  fpu_fpsr_t fpsr;
   int round;
 
   _FPU_GETCW (fpcr);
-  _FPU_GETFPSR (fpsr);
-  ctx->env.__fpsr = fpsr;
 
   /* Check whether rounding modes are different.  */
   round = (fpcr ^ r) & _FPU_FPCR_RM_MASK;
@@ -264,6 +261,33 @@ libc_feresetround_aarch64_ctx (struct rm_ctx *ctx)
 #define libc_feresetroundl_ctx         libc_feresetround_aarch64_ctx
 
 static __always_inline void
+libc_feholdsetround_noex_aarch64_ctx (struct rm_ctx *ctx, int r)
+{
+  fpu_control_t fpcr;
+  fpu_fpsr_t fpsr;
+  int round;
+
+  _FPU_GETCW (fpcr);
+  _FPU_GETFPSR (fpsr);
+  ctx->env.__fpsr = fpsr;
+
+  /* Check whether rounding modes are different.  */
+  round = (fpcr ^ r) & _FPU_FPCR_RM_MASK;
+  ctx->updated_status = round != 0;
+
+  /* Set the rounding mode if changed.  */
+  if (__glibc_unlikely (round != 0))
+    {
+      ctx->env.__fpcr = fpcr;
+      _FPU_SETCW (fpcr ^ round);
+    }
+}
+
+#define libc_feholdsetround_noex_ctx   libc_feholdsetround_noex_aarch64_ctx
+#define libc_feholdsetround_noexf_ctx  libc_feholdsetround_noex_aarch64_ctx
+#define libc_feholdsetround_noexl_ctx  libc_feholdsetround_noex_aarch64_ctx
+
+static __always_inline void
 libc_feresetround_noex_aarch64_ctx (struct rm_ctx *ctx)
 {
   /* Restore the rounding mode if updated.  */