x86_64: Integer min/max improvements.

This patch tweaks the way that min and max are expanded, so that the
semantics of these operations are visible to the early RTL optimization
passes, until split into explicit comparison and conditional move
instructions. The good news is that i386.md already contains all of
the required logic (many thanks to Richard Biener and Uros Bizjak),
but this is currently only enabled to scalar-to-vector (STV) synthesis
of min/max instructions.  This change enables this functionality for
all TARGET_CMOVE architectures for SImode, HImode and DImode.

2020-08-06  Roger Sayle  <roger@nextmovesoftware.com>
	    Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog
	* config/i386/i386.md (MAXMIN_IMODE): No longer needed.
	(<maxmin><mode>3):  Support SWI248 and general_operand for
	second operand, when TARGET_CMOVE.
	(<maxmin><mode>3_1 splitter): Optimize comparisons against
	0, 1 and -1 to use "test" instead of "cmp".
	(*<maxmin>di3_doubleword): Likewise, allow general_operand
	and enable on TARGET_CMOVE.
	(peephole2): Convert clearing a register after a flag setting
	instruction into an xor followed by the original flag setter.

gcc/testsuite/ChangeLog
	* gcc.target/i386/minmax-8.c: New test.
	* gcc.target/i386/minmax-9.c: New test.
	* gcc.target/i386/minmax-10.c: New test.
	* gcc.target/i386/minmax-11.c: New test.

gcc/config/i386/i386.md

@@ -18809,45 +18809,68 @@
 
 ;; min/max patterns
 
-(define_mode_iterator MAXMIN_IMODE
-  [(SI "TARGET_SSE4_1") (DI "TARGET_AVX512VL")])
 (define_code_attr maxmin_rel
   [(smax "GE") (smin "LE") (umax "GEU") (umin "LEU")])
 
 (define_expand "<code><mode>3"
   [(parallel
-    [(set (match_operand:MAXMIN_IMODE 0 "register_operand")
-	  (maxmin:MAXMIN_IMODE
-	    (match_operand:MAXMIN_IMODE 1 "register_operand")
-	    (match_operand:MAXMIN_IMODE 2 "nonimmediate_operand")))
+    [(set (match_operand:SWI248 0 "register_operand")
+	  (maxmin:SWI248
+	    (match_operand:SWI248 1 "register_operand")
+	    (match_operand:SWI248 2 "general_operand")))
      (clobber (reg:CC FLAGS_REG))])]
-  "TARGET_STV")
+  "TARGET_CMOVE")
 
 (define_insn_and_split "*<code><mode>3_1"
-  [(set (match_operand:MAXMIN_IMODE 0 "register_operand")
-	(maxmin:MAXMIN_IMODE
-	  (match_operand:MAXMIN_IMODE 1 "register_operand")
-	  (match_operand:MAXMIN_IMODE 2 "nonimmediate_operand")))
+  [(set (match_operand:SWI248 0 "register_operand")
+	(maxmin:SWI248
+	  (match_operand:SWI248 1 "register_operand")
+	  (match_operand:SWI248 2 "general_operand")))
    (clobber (reg:CC FLAGS_REG))]
-  "(TARGET_64BIT || <MODE>mode != DImode) && TARGET_STV
+  "TARGET_CMOVE
    && ix86_pre_reload_split ()"
   "#"
   "&& 1"
   [(set (match_dup 0)
-	(if_then_else:MAXMIN_IMODE (match_dup 3)
+	(if_then_else:SWI248 (match_dup 3)
 	  (match_dup 1)
 	  (match_dup 2)))]
 {
   machine_mode mode = <MODE>mode;
+  rtx cmp_op = operands[2];
 
-  if (!register_operand (operands[2], mode))
-    operands[2] = force_reg (mode, operands[2]);
+  if (!register_operand (cmp_op, mode))
+    operands[2] = force_reg (mode, cmp_op);
 
   enum rtx_code code = <maxmin_rel>;
-  machine_mode cmpmode = SELECT_CC_MODE (code, operands[1], operands[2]);
+
+  if (cmp_op == const1_rtx)
+    {
+      /* Convert smax (x, 1) into (x > 0 ? x : 1).
+	 Convert umax (x, 1) into (x != 0 ? x : 1).
+	 Convert ?min (x, 1) into (x <= 0 ? x : 1).  */
+      cmp_op = const0_rtx;
+      if (code == GE)
+	code = GT;
+      else if (code == GEU)
+	code = NE;
+    }
+  /* Convert smin (x, -1) into (x < 0 ? x : -1).  */
+  else if (cmp_op == constm1_rtx && code == LE)
+    {
+      cmp_op = const0_rtx;
+      code = LT;
+    }
+  /* Convert smax (x, -1) into (x >= 0 ? x : -1).  */
+  else if (cmp_op == constm1_rtx && code == GE)
+    cmp_op = const0_rtx;
+  else if (cmp_op != const0_rtx)
+    cmp_op = operands[2];
+
+  machine_mode cmpmode = SELECT_CC_MODE (code, operands[1], cmp_op);
   rtx flags = gen_rtx_REG (cmpmode, FLAGS_REG);
 
-  rtx tmp = gen_rtx_COMPARE (cmpmode, operands[1], operands[2]);
+  rtx tmp = gen_rtx_COMPARE (cmpmode, operands[1], cmp_op);
   emit_insn (gen_rtx_SET (flags, tmp));
 
   operands[3] = gen_rtx_fmt_ee (code, VOIDmode, flags, const0_rtx);
@@ -18856,9 +18879,9 @@
 (define_insn_and_split "*<code>di3_doubleword"
   [(set (match_operand:DI 0 "register_operand")
 	(maxmin:DI (match_operand:DI 1 "register_operand")
-		   (match_operand:DI 2 "nonimmediate_operand")))
+		   (match_operand:DI 2 "general_operand")))
    (clobber (reg:CC FLAGS_REG))]
-  "!TARGET_64BIT && TARGET_STV && TARGET_AVX512VL
+  "!TARGET_64BIT && TARGET_CMOVE
    && ix86_pre_reload_split ()"
   "#"
   "&& 1"
@@ -18910,6 +18933,19 @@
       gcc_unreachable ();
     }
 })
+
+;; Avoid clearing a register between a flags setting comparison and its use,
+;; i.e. prefer "xorl %eax,%eax; test/cmp" over "test/cmp; movl $0, %eax".
+(define_peephole2
+  [(set (reg FLAGS_REG) (match_operand 0))
+   (set (match_operand:SWI 1 "register_operand") (const_int 0))]
+  "peep2_regno_dead_p (0, FLAGS_REG)
+   && !reg_overlap_mentioned_p (operands[1], operands[0])"
+   [(set (match_dup 2) (match_dup 0))]
+{
+  operands[2] = gen_rtx_REG (GET_MODE (operands[0]), FLAGS_REG);
+  ix86_expand_clear (operands[1]);
+})
 
 ;; Misc patterns (?)
 

gcc/testsuite/gcc.target/i386/minmax-10.c

@@ -0,0 +1,38 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+#define max(a,b) (((a) > (b))? (a) : (b))
+#define min(a,b) (((a) < (b))? (a) : (b))
+
+int smax1(int x)
+{
+  return max(x,1);
+}
+
+int smin1(int x)
+{
+  return min(x,1);
+}
+
+int smaxm1(int x)
+{
+  return max(x,-1);
+}
+
+int sminm1(int x)
+{
+  return min(x,-1);
+}
+
+unsigned int umax1(unsigned int x)
+{
+  return max(x,1);
+}
+
+unsigned int umin1(unsigned int x)
+{
+  return min(x,1);
+}
+
+/* { dg-final { scan-assembler-times "test" 6 } } */
+/* { dg-final { scan-assembler-not "cmp" } } */

gcc/testsuite/gcc.target/i386/minmax-11.c

@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-reassoc" } */
+
+#define max(a,b) (((a) > (b))? (a) : (b))
+
+int foo(int x)
+{
+  int y = max(x,12345);
+  return max(y,87654);
+}
+
+/* { dg-final { scan-assembler-not "12345" } } */

gcc/testsuite/gcc.target/i386/minmax-8.c

@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-Os" } */
+
+#define max(a,b) (((a) > (b))? (a) : (b))
+#define min(a,b) (((a) < (b))? (a) : (b))
+
+int foo(int x)
+{
+  return max(x,12345);
+}
+
+int bar(int x)
+{
+  return min(x,87654);
+}
+
+/* { dg-final { scan-assembler-times "12345" 1 } } */
+/* { dg-final { scan-assembler-times "87654" 1 } } */

gcc/testsuite/gcc.target/i386/minmax-9.c

@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-Os" } */
+
+#define max(a,b) (((a) > (b))? (a) : (b))
+#define min(a,b) (((a) < (b))? (a) : (b))
+
+int foo(int x)
+{
+  return max(x,0);
+}
+
+int bar(int x)
+{
+  return min(x,0);
+}
+
+unsigned int baz(unsigned int x)
+{
+  return min(x,1);
+}
+
+/* { dg-final { scan-assembler-times "xor" 3 } } */
+/* { dg-final { scan-assembler-times "test" 3 } } */