i386: Optimize popcnt followed by zero/sign extension [PR91824]

Like any other instruction with 32-bit GPR destination operand in 64-bit
mode, popcntl also clears the upper 32 bits of the register (and other bits
too, it can return only 0 to 32 inclusive).

During combine, the zero or sign extensions of it show up as paradoxical
subreg of the popcount & 63, there 63 is the smallest power of two - 1 mask
that can represent all the 0 to 32 inclusive values.

2020-01-30  Jakub Jelinek  <jakub@redhat.com>

	PR target/91824
	* config/i386/i386.md (*popcountsi2_zext): New define_insn_and_split.
	(*popcountsi2_zext_falsedep): New define_insn.

	* gcc.target/i386/pr91824-1.c: New test.

gcc/ChangeLog

@@ -1,3 +1,9 @@
+2020-01-30  Jakub Jelinek  <jakub@redhat.com>
+
+	PR target/91824
+	* config/i386/i386.md (*popcountsi2_zext): New define_insn_and_split.
+	(*popcountsi2_zext_falsedep): New define_insn.
+
 2020-01-30  Dragan Mladjenovic  <dmladjenovic@wavecomp.com>
 
 	* config.in: Regenerated.

gcc/config/i386/i386.md

@@ -14563,6 +14563,60 @@
    (set_attr "type" "bitmanip")
    (set_attr "mode" "<MODE>")])
 
+(define_insn_and_split "*popcountsi2_zext"
+  [(set (match_operand:DI 0 "register_operand" "=r")
+	(and:DI
+	  (subreg:DI
+	    (popcount:SI
+	      (match_operand:SI 1 "nonimmediate_operand" "rm")) 0)
+	  (const_int 63)))
+   (clobber (reg:CC FLAGS_REG))]
+  "TARGET_POPCNT && TARGET_64BIT"
+{
+#if TARGET_MACHO
+  return "popcnt\t{%1, %k0|%k0, %1}";
+#else
+  return "popcnt{l}\t{%1, %k0|%k0, %1}";
+#endif
+}
+  "&& TARGET_AVOID_FALSE_DEP_FOR_BMI && epilogue_completed
+   && optimize_function_for_speed_p (cfun)
+   && !reg_mentioned_p (operands[0], operands[1])"
+  [(parallel
+    [(set (match_dup 0)
+	  (and:DI (subreg:DI (popcount:SI (match_dup 1)) 0) (const_int 63)))
+     (unspec [(match_dup 0)] UNSPEC_INSN_FALSE_DEP)
+     (clobber (reg:CC FLAGS_REG))])]
+  "ix86_expand_clear (operands[0]);"
+  [(set_attr "prefix_rep" "1")
+   (set_attr "type" "bitmanip")
+   (set_attr "mode" "SI")])
+
+; False dependency happens when destination is only updated by tzcnt,
+; lzcnt or popcnt.  There is no false dependency when destination is
+; also used in source.
+(define_insn "*popcountsi2_zext_falsedep"
+  [(set (match_operand:DI 0 "register_operand" "=r")
+	(and:DI
+	  (subreg:DI
+	    (popcount:SI
+	      (match_operand:SI 1 "nonimmediate_operand" "rm")) 0)
+	  (const_int 63)))
+   (unspec [(match_operand:DI 2 "register_operand" "0")]
+	   UNSPEC_INSN_FALSE_DEP)
+   (clobber (reg:CC FLAGS_REG))]
+  "TARGET_POPCNT && TARGET_64BIT"
+{
+#if TARGET_MACHO
+  return "popcnt\t{%1, %k0|%k0, %1}";
+#else
+  return "popcnt{l}\t{%1, %k0|%k0, %1}";
+#endif
+}
+  [(set_attr "prefix_rep" "1")
+   (set_attr "type" "bitmanip")
+   (set_attr "mode" "SI")])
+
 (define_insn_and_split "*popcounthi2_1"
   [(set (match_operand:SI 0 "register_operand")
 	(popcount:SI

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2020-01-30  Jakub Jelinek  <jakub@redhat.com>
+
+	PR target/91824
+	* gcc.target/i386/pr91824-1.c: New test.
+
 2020-01-30  Bin Cheng  <bin.cheng@linux.alibaba.com>
 
 	* g++.dg/coroutines/co-await-syntax-09-convert.C: New test.

gcc/testsuite/gcc.target/i386/pr91824-1.c

@@ -0,0 +1,54 @@
+/* PR target/91824 */
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O2 -mpopcnt" } */
+/* { dg-final { scan-assembler-not "cltq" } } */
+
+unsigned int foo (void);
+
+unsigned long
+f1 (unsigned int x)
+{
+  return __builtin_popcount (x);
+}
+
+unsigned long
+f2 (unsigned int x)
+{
+  return (unsigned) __builtin_popcount (x);
+}
+
+unsigned long
+f3 (unsigned int x)
+{
+  return __builtin_popcount (x) & 63ULL;
+}
+
+unsigned long
+f4 (unsigned int x)
+{
+  return __builtin_popcount (x) & 1023ULL;
+}
+
+unsigned long
+f5 (void)
+{
+  return __builtin_popcount (foo ());
+}
+
+unsigned long
+f6 (void)
+{
+  return (unsigned) __builtin_popcount (foo ());
+}
+
+unsigned long
+f7 (void)
+{
+  return __builtin_popcount (foo ()) & 63ULL;
+}
+
+unsigned long
+f8 (void)
+{
+  return __builtin_popcount (foo ()) & 1023ULL;
+}