Rename the tuning option and related functions to enable the Newton series for the reciprocal square root to reflect its approximative characteristic.

gcc/
	* config/aarch64/aarch64-protos.h (aarch64_emit_swrsqrt): Rename
	function to "aarch64_emit_approx_rsqrt".
	* config/aarch64/aarch64-tuning-flags.def: Rename tuning flag to
	AARCH64_EXTRA_TUNE_APPROX_RSQRT.
	* config/aarch64/aarch64.c (exynosm1_tunigs): Use new flag name.
	(xgene1_tunings): Likewise.
	(use_rsqrt_p): Likewise.
	(aarch64_emit_swrsqrt): Use new function name.
	* config/aarch64/aarch64-simd.md (aarch64_rsqrts_*): Likewise.
	* config/aarch64/aarch64.opt (mlow-precision-recip-sqrt): Reword the
	text explaining this option.
	* doc/invoke.texi (-mlow-precision-recip-sqrt): Likewise.

From-SVN: r233772

7 files changed, 41 insertions, 25 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 471fea5..8cece6b 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,23 @@
+2016-02-26  Evandro Menezes  <e.menezes@samsung.com>
+
+	Rename the AArch64 tuning option and related functions to enable the
+	Newton series for the reciprocal square root to reflect its
+	approximative characteristic.
+
+	gcc/
+	* config/aarch64/aarch64-protos.h (aarch64_emit_swrsqrt): Rename
+	function to "aarch64_emit_approx_rsqrt".
+	* config/aarch64/aarch64-tuning-flags.def: Rename tuning flag to
+	AARCH64_EXTRA_TUNE_APPROX_RSQRT.
+	* config/aarch64/aarch64.c (exynosm1_tunigs): Use new flag name.
+	(xgene1_tunings): Likewise.
+	(use_rsqrt_p): Likewise.
+	(aarch64_emit_swrsqrt): Use new function name.
+	* config/aarch64/aarch64-simd.md (aarch64_rsqrts_*): Likewise.
+	* config/aarch64/aarch64.opt (mlow-precision-recip-sqrt): Reword the
+	text explaining this option.
+	* doc/invoke.texi (-mlow-precision-recip-sqrt): Likewise.
+
 2016-02-26  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/69969
diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
index 78870e2..acf2062 100644
--- a/gcc/config/aarch64/aarch64-protos.h
+++ b/gcc/config/aarch64/aarch64-protos.h
@@ -360,8 +360,7 @@ void aarch64_emit_call_insn (rtx);
 void aarch64_register_pragmas (void);
 void aarch64_relayout_simd_types (void);
 void aarch64_reset_previous_fndecl (void);
-
-void aarch64_emit_swrsqrt (rtx, rtx);
+void aarch64_emit_approx_rsqrt (rtx, rtx);
 
 /* Initialize builtins for SIMD intrinsics.  */
 void init_aarch64_simd_builtins (void);
@@ -413,9 +412,7 @@ rtx aarch64_expand_builtin (tree exp,
 			    machine_mode mode ATTRIBUTE_UNUSED,
 			    int ignore ATTRIBUTE_UNUSED);
 tree aarch64_builtin_decl (unsigned, bool ATTRIBUTE_UNUSED);
-
 tree aarch64_builtin_rsqrt (unsigned int);
-
 tree aarch64_builtin_vectorized_function (unsigned int, tree, tree);
 
 extern void aarch64_split_combinev16qi (rtx operands[3]);
diff --git a/gcc/config/aarch64/aarch64-simd.md b/gcc/config/aarch64/aarch64-simd.md
index d8497ab..bd73bce 100644
--- a/gcc/config/aarch64/aarch64-simd.md
+++ b/gcc/config/aarch64/aarch64-simd.md
@@ -405,7 +405,7 @@
 		     UNSPEC_RSQRT))]
   "TARGET_SIMD"
 {
-  aarch64_emit_swrsqrt (operands[0], operands[1]);
+  aarch64_emit_approx_rsqrt (operands[0], operands[1]);
   DONE;
 })
 
diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def b/gcc/config/aarch64/aarch64-tuning-flags.def
index 8036cfe..7e45a0c 100644
--- a/gcc/config/aarch64/aarch64-tuning-flags.def
+++ b/gcc/config/aarch64/aarch64-tuning-flags.def
@@ -29,5 +29,5 @@
      AARCH64_TUNE_ to give an enum name. */
 
 AARCH64_EXTRA_TUNING_OPTION ("rename_fma_regs", RENAME_FMA_REGS)
-AARCH64_EXTRA_TUNING_OPTION ("recip_sqrt", RECIP_SQRT)
+AARCH64_EXTRA_TUNING_OPTION ("approx_rsqrt", APPROX_RSQRT)
 
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 3519c7b..801f95a 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -538,7 +538,7 @@ static const struct tune_params exynosm1_tunings =
   48,	/* max_case_values.  */
   64,	/* cache_line_size.  */
   tune_params::AUTOPREFETCHER_OFF, /* autoprefetcher_model.  */
-  (AARCH64_EXTRA_TUNE_RECIP_SQRT) /* tune_flags.  */
+  (AARCH64_EXTRA_TUNE_APPROX_RSQRT) /* tune_flags.  */
 };
 
 static const struct tune_params thunderx_tunings =
@@ -586,7 +586,7 @@ static const struct tune_params xgene1_tunings =
   0,	/* max_case_values.  */
   0,	/* cache_line_size.  */
   tune_params::AUTOPREFETCHER_OFF,	/* autoprefetcher_model.  */
-  (AARCH64_EXTRA_TUNE_RECIP_SQRT)	/* tune_flags.  */
+  (AARCH64_EXTRA_TUNE_APPROX_RSQRT)	/* tune_flags.  */
 };
 
 /* Support for fine-grained override of the tuning structures.  */
@@ -7460,8 +7460,8 @@ aarch64_memory_move_cost (machine_mode mode ATTRIBUTE_UNUSED,
   return aarch64_tune_params.memmov_cost;
 }
 
-/* Return true if it is safe and beneficial to use the rsqrt optabs to
-   optimize 1.0/sqrt.  */
+/* Return true if it is safe and beneficial to use the approximate rsqrt optabs
+   to optimize 1.0/sqrt.  */
 
 static bool
 use_rsqrt_p (void)
@@ -7469,12 +7469,12 @@ use_rsqrt_p (void)
   return (!flag_trapping_math
 	  && flag_unsafe_math_optimizations
 	  && ((aarch64_tune_params.extra_tuning_flags
-	       & AARCH64_EXTRA_TUNE_RECIP_SQRT)
+	       & AARCH64_EXTRA_TUNE_APPROX_RSQRT)
 	      || flag_mrecip_low_precision_sqrt));
 }
 
-/* Function to decide when to use
-   reciprocal square root builtins.  */
+/* Function to decide when to use the approximate reciprocal square root
+   builtin.  */
 
 static tree
 aarch64_builtin_reciprocal (tree fndecl)
@@ -7522,12 +7522,12 @@ get_rsqrts_type (machine_mode mode)
   }
 }
 
-/* Emit instruction sequence to compute
-   reciprocal square root.  Use two Newton-Raphson steps
-   for single precision and three for double precision.  */
+/* Emit instruction sequence to compute the reciprocal square root using the
+   Newton-Raphson series.  Iterate over the series twice for SF
+   and thrice for DF.  */
 
 void
-aarch64_emit_swrsqrt (rtx dst, rtx src)
+aarch64_emit_approx_rsqrt (rtx dst, rtx src)
 {
   machine_mode mode = GET_MODE (src);
   gcc_assert (
@@ -7544,6 +7544,7 @@ aarch64_emit_swrsqrt (rtx dst, rtx src)
 
   int iterations = double_mode ? 3 : 2;
 
+  /* Optionally iterate over the series one less time than otherwise.  */
   if (flag_mrecip_low_precision_sqrt)
     iterations--;
 
diff --git a/gcc/config/aarch64/aarch64.opt b/gcc/config/aarch64/aarch64.opt
index 5cbd4cd..49ef0c6 100644
--- a/gcc/config/aarch64/aarch64.opt
+++ b/gcc/config/aarch64/aarch64.opt
@@ -151,5 +151,5 @@ PC relative literal loads.
 
 mlow-precision-recip-sqrt
 Common Var(flag_mrecip_low_precision_sqrt) Optimization
-When calculating a sqrt approximation, run fewer steps.
-This reduces precision, but can result in faster computation.
+When calculating the reciprocal square root approximation,
+uses one less step than otherwise, thus reducing latency and precision.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 18b2b8f..4b5df0b 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -12884,12 +12884,10 @@ corresponding flag to the linker.
 @item -mno-low-precision-recip-sqrt
 @opindex -mlow-precision-recip-sqrt
 @opindex -mno-low-precision-recip-sqrt
-The square root estimate uses two steps instead of three for double-precision,
-and one step instead of two for single-precision.
-Thus reducing latency and precision.
-This is only relevant if @option{-ffast-math} activates
-reciprocal square root estimate instructions.
-Which in turn depends on the target processor.
+When calculating the reciprocal square root approximation,
+uses one less step than otherwise, thus reducing latency and precision.
+This is only relevant if @option{-ffast-math} enables the reciprocal square root
+approximation, which in turn depends on the target processor.
 
 @item -march=@var{name}
 @opindex march