aarch64: Emit single-instruction for smin (x, 0) and smax (x, 0)

Motivated by https://reviews.llvm.org/D148249, we can expand to a single instruction
for the SMIN (x, 0) and SMAX (x, 0) cases using the combined AND/BIC and ASR operations.
Given that we already have well-fitting TARGET_CSSC patterns and expanders for the min/max codes
in the backend this patch does some minor refactoring to ensure we emit the right SMAX/SMIN RTL codes
for TARGET_CSSC, fall back to the generic expanders or emit a simple SMIN/SMAX with 0 RTX for !TARGET_CSSC
that is now matched by a separate pattern.

Bootstrapped and tested on aarch64-none-linux-gnu.

gcc/ChangeLog:

	* config/aarch64/aarch64.md (aarch64_umax<mode>3_insn): Delete.
	(umax<mode>3): Emit raw UMAX RTL instead of going through gen_ function
	for umax.
	(<optab><mode>3): New define_expand for MAXMIN_NOUMAX codes.
	(*aarch64_<optab><mode>3_zero): Define.
	(*aarch64_<optab><mode>3_cssc): Likewise.
	* config/aarch64/iterators.md (maxminand): New code attribute.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sminmax-asr_1.c: New test.

3 files changed, 97 insertions, 15 deletions

diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index f46d738..eaa87bf 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -4412,17 +4412,6 @@
   [(set_attr "type" "csel")]
 )
 
-(define_insn "aarch64_umax<mode>3_insn"
-  [(set (match_operand:GPI 0 "register_operand" "=r,r")
-        (umax:GPI (match_operand:GPI 1 "register_operand" "r,r")
-		(match_operand:GPI 2 "aarch64_uminmax_operand" "r,Uum")))]
-  "TARGET_CSSC"
-  "@
-   umax\\t%<w>0, %<w>1, %<w>2
-   umax\\t%<w>0, %<w>1, %2"
-  [(set_attr "type" "alu_sreg,alu_imm")]
-)
-
 ;; If X can be loaded by a single CNT[BHWD] instruction,
 ;;
 ;;    A = UMAX (B, X)
@@ -4466,8 +4455,8 @@
 	operands[1] = force_reg (<MODE>mode, operands[1]);
 	if (!aarch64_uminmax_operand (operands[2], <MODE>mode))
 	  operands[2] = force_reg (<MODE>mode, operands[2]);
-	emit_insn (gen_aarch64_umax<mode>3_insn (operands[0], operands[1],
-						 operands[2]));
+	emit_move_insn (operands[0], gen_rtx_UMAX (<MODE>mode, operands[1],
+						   operands[2]));
 	DONE;
       }
     else
@@ -6759,9 +6748,30 @@
   [(set_attr "type" "ffarith<stype>")]
 )
 
-(define_insn "<optab><mode>3"
+;; Expander for integer smin, smax, umin.  Mainly used to generate
+;; straightforward RTL for TARGET_CSSC.  When that is not available
+;; FAIL and let the generic expanders generate the CMP + CSEL sequences,
+;; except for the SMIN and SMAX with zero cases, for which we have a
+;; single instruction even for the base architecture.
+(define_expand "<optab><mode>3"
+  [(set (match_operand:GPI 0 "register_operand")
+        (MAXMIN_NOUMAX:GPI
+	  (match_operand:GPI 1 "register_operand")
+	  (match_operand:GPI 2 "aarch64_<su>minmax_operand")))]
+  ""
+  {
+    if (!TARGET_CSSC)
+      {
+	if (operands[2] != CONST0_RTX (<MODE>mode)
+	    || !(<CODE> == SMAX || <CODE> == SMIN))
+	  FAIL;
+      }
+  }
+)
+
+(define_insn "*aarch64_<optab><mode>3_cssc"
   [(set (match_operand:GPI 0 "register_operand" "=r,r")
-        (MAXMIN_NOUMAX:GPI (match_operand:GPI 1 "register_operand" "r,r")
+        (MAXMIN:GPI (match_operand:GPI 1 "register_operand" "r,r")
 		(match_operand:GPI 2 "aarch64_<su>minmax_operand" "r,U<su>m")))]
   "TARGET_CSSC"
   "@
@@ -6770,6 +6780,16 @@
   [(set_attr "type" "alu_sreg,alu_imm")]
 )
 
+(define_insn "*aarch64_<optab><mode>3_zero"
+  [(set (match_operand:GPI 0 "register_operand" "=r")
+        (FMAXMIN:GPI
+	  (match_operand:GPI 1 "register_operand" "r")
+	  (const_int 0)))]
+  ""
+  "<maxminand>\\t%<w>0, %<w>1, %<w>1, asr <sizem1>";
+  [(set_attr "type" "logic_shift_imm")]
+)
+
 ;; Given that smax/smin do not specify the result when either input is NaN,
 ;; we could use either FMAXNM or FMAX for smax, and either FMINNM or FMIN
 ;; for smin.
diff --git a/gcc/config/aarch64/iterators.md b/gcc/config/aarch64/iterators.md
index d3c43a2..d0184c8 100644
--- a/gcc/config/aarch64/iterators.md
+++ b/gcc/config/aarch64/iterators.md
@@ -2435,6 +2435,8 @@
 			  (umax "max")
 			  (umin "min")])
 
+(define_code_attr maxminand [(smax "bic") (smin "and")])
+
 ;; MLA/MLS attributes.
 (define_code_attr as [(ss_plus "a") (ss_minus "s")])
 
diff --git a/gcc/testsuite/gcc.target/aarch64/sminmax-asr_1.c b/gcc/testsuite/gcc.target/aarch64/sminmax-asr_1.c
new file mode 100644
index 0000000..63396ec
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sminmax-asr_1.c
@@ -0,0 +1,60 @@
+/* { dg-do compile } */
+/* { dg-options "-O --save-temps" } */
+/* { dg-final { check-function-bodies "**" "" "" } } */
+
+#include <stdint.h>
+
+#pragma GCC target "+nocssc"
+
+#define MAX(X, Y) ((X) > (Y) ? (X) : (Y))
+#define MIN(X, Y) ((X) < (Y) ? (X) : (Y))
+
+
+/*
+** minzero:
+**	and	w0, w0, w0, asr #31
+**	ret
+*/
+
+int32_t
+minzero (int32_t a)
+{
+  return MIN (a, 0);
+}
+
+/*
+** maxzero:
+**	bic	w0, w0, w0, asr #31
+**	ret
+*/
+
+int32_t
+maxzero (int32_t a)
+{
+  return MAX (a, 0);
+}
+
+/*
+** minzerol:
+**	and	x0, x0, x0, asr #63
+**	ret
+*/
+
+int64_t
+minzerol (int64_t a)
+{
+  return MIN (a, 0);
+}
+
+/*
+** maxzerol:
+**	bic	x0, x0, x0, asr #63
+**	ret
+*/
+
+int64_t
+maxzerol (int64_t a)
+{
+  return MAX (a, 0);
+}
+