re PR target/93002 (while(i--) optimization)

	PR target/93002
	* config/i386/i386.md (dec reg; cmp $-1, reg; jne lab): New
	define_peephole2.

	* gcc.target/i386/pr93002.c: New test.

From-SVN: r279632

gcc/ChangeLog

+2019-12-20  Jakub Jelinek  <jakub@redhat.com>
+
+	PR target/93002
+	* config/i386/i386.md (dec reg; cmp $-1, reg; jne lab): New
+	define_peephole2.
+
 2019-12-19  Julian Brown  <julian@codesourcery.com>
 
 	* gimplify.c (gimplify_omp_var_data): Add GOVD_MAP_HAS_ATTACHMENTS.

gcc/config/i386/i386.md

@@ -6503,6 +6503,36 @@
   [(set (reg:CC FLAGS_REG)
 	(compare:CC (match_dup 0) (match_dup 1)))])
 
+;; decl %eax; cmpl $-1, %eax; jne .Lxx; can be optimized into
+;; subl $1, %eax; jnc .Lxx;
+(define_peephole2
+  [(parallel
+     [(set (match_operand:SWI 0 "general_reg_operand")
+	   (plus:SWI (match_dup 0) (const_int -1)))
+      (clobber (reg FLAGS_REG))])
+   (set (reg:CCZ FLAGS_REG)
+	(compare:CCZ (match_dup 0) (const_int -1)))
+   (set (pc)
+	(if_then_else (match_operator 1 "bt_comparison_operator"
+			[(reg:CCZ FLAGS_REG) (const_int 0)])
+		      (match_operand 2)
+		      (pc)))]
+   "peep2_regno_dead_p (3, FLAGS_REG)"
+   [(parallel
+      [(set (reg:CC FLAGS_REG)
+	    (compare:CC (match_dup 0) (const_int 1)))
+       (set (match_dup 0)
+	    (minus:SWI (match_dup 0) (const_int 1)))])
+    (set (pc)
+	 (if_then_else (match_dup 3)
+		       (match_dup 2)
+		       (pc)))]
+{
+  rtx cc = gen_rtx_REG (CCmode, FLAGS_REG);
+  operands[3] = gen_rtx_fmt_ee (GET_CODE (operands[1]) == NE
+				? GEU : LTU, VOIDmode, cc, const0_rtx);
+})
+
 (define_insn "*subsi_3_zext"
   [(set (reg FLAGS_REG)
 	(compare (match_operand:SI 1 "register_operand" "0")

gcc/testsuite/ChangeLog

+2019-12-20  Jakub Jelinek  <jakub@redhat.com>
+
+	PR target/93002
+	* gcc.target/i386/pr93002.c: New test.
+
 2019-12-19  Julian Brown  <julian@codesourcery.com>
 
         * gfortran.dg/goacc/derived-types.f90: New test.

gcc/testsuite/gcc.target/i386/pr93002.c

+/* PR target/93002 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler-not "cmp\[^\n\r]*-1" } } */
+
+volatile int sink;
+
+void
+foo (void)
+{
+  unsigned i = 1000;
+  while (i--)
+    sink = i;
+}
+
+void
+bar (void)
+{
+  int i = 2000;
+  while (i--)
+    sink = i;
+}