loongarch: add alternatives for idiv insns to improve code generation

Currently in the description of LoongArch integer division instructions,
the output is marked as earlyclobbered ('&').  It's necessary when
loongarch_check_zero_div_p() because clobbering operand 2 (divisor) will
make the checking for zero divisor impossible.

But, for -mno-check-zero-division (the default of GCC >= 12.2 for
optimized code), the output is not earlyclobbered at all.  And, the
read of operand 1 only occurs before clobbering the output.  So we make
three alternatives for an idiv instruction:

* (=r,r,r): For -mno-check-zero-division.
* (=&r,r,r): For -mcheck-zero-division.
* (=&r,0,r): For -mcheck-zero-division, to explicitly allow patterns
  like "div.d $a0, $a0, $a1".

gcc/ChangeLog:

	* config/loongarch/loongarch.cc (loongarch_check_zero_div_p):
	Remove static, for use in the machine description file.
	* config/loongarch/loongarch-protos.h:
	(loongarch_check_zero_div_p): Add prototype.
	* config/loongarch/loongarch.md (enabled): New attr.
	(*<optab><mode>3): Add (=r,r,r) and (=&r,0,r) alternatives for
	idiv.  Conditionally enable the alternatives using
	loongarch_check_zero_div_p.
	(<optab>di3_fake): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/div-1.c: New test.
	* gcc.target/loongarch/div-2.c: New test.
	* gcc.target/loongarch/div-3.c: New test.

gcc/config/loongarch/loongarch-protos.h

@@ -130,6 +130,7 @@ extern bool loongarch_symbol_binds_local_p (const_rtx);
 extern const char *current_section_name (void);
 extern unsigned int current_section_flags (void);
 extern bool loongarch_use_ins_ext_p (rtx, HOST_WIDE_INT, HOST_WIDE_INT);
+extern bool loongarch_check_zero_div_p (void);
 
 union loongarch_gen_fn_ptrs
 {

gcc/config/loongarch/loongarch.cc

@@ -2110,7 +2110,7 @@ loongarch_load_store_insns (rtx mem, rtx_insn *insn)
 
 /* Return true if we need to trap on division by zero.  */
 
-static bool
+bool
 loongarch_check_zero_div_p (void)
 {
   /* if -m[no-]check-zero-division is given explicitly.  */

gcc/config/loongarch/loongarch.md

@@ -110,6 +110,8 @@
 ;;
 ;; ....................
 
+(define_attr "enabled" "no,yes" (const_string "yes"))
+
 (define_attr "got" "unset,load"
   (const_string "unset"))
 
@@ -763,26 +765,36 @@
 })
 
 (define_insn "*<optab><mode>3"
-  [(set (match_operand:GPR 0 "register_operand" "=&r")
-	(any_div:GPR (match_operand:GPR 1 "register_operand" "r")
-		     (match_operand:GPR 2 "register_operand" "r")))]
+  [(set (match_operand:GPR 0 "register_operand" "=r,&r,&r")
+	(any_div:GPR (match_operand:GPR 1 "register_operand" "r,r,0")
+		     (match_operand:GPR 2 "register_operand" "r,r,r")))]
   ""
 {
   return loongarch_output_division ("<insn>.<d><u>\t%0,%1,%2", operands);
 }
   [(set_attr "type" "idiv")
-   (set_attr "mode" "<MODE>")])
+   (set_attr "mode" "<MODE>")
+   (set (attr "enabled")
+      (if_then_else
+	(match_test "!!which_alternative == loongarch_check_zero_div_p()")
+	(const_string "yes")
+	(const_string "no")))])
 
 (define_insn "<optab>di3_fake"
-  [(set (match_operand:SI 0 "register_operand" "=&r")
-	(any_div:SI (match_operand:DI 1 "register_operand" "r")
-		    (match_operand:DI 2 "register_operand" "r")))]
+  [(set (match_operand:SI 0 "register_operand" "=r,&r,&r")
+	(any_div:SI (match_operand:DI 1 "register_operand" "r,r,0")
+		    (match_operand:DI 2 "register_operand" "r,r,r")))]
   ""
 {
   return loongarch_output_division ("<insn>.w<u>\t%0,%1,%2", operands);
 }
   [(set_attr "type" "idiv")
-   (set_attr "mode" "SI")])
+   (set_attr "mode" "SI")
+   (set (attr "enabled")
+      (if_then_else
+	(match_test "!!which_alternative == loongarch_check_zero_div_p()")
+	(const_string "yes")
+	(const_string "no")))])
 
 ;; Floating point multiply accumulate instructions.
 

gcc/testsuite/gcc.target/loongarch/div-1.c

@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mcheck-zero-division" } */
+/* { dg-final { scan-assembler "div.\[wd\]\t\\\$r4,\\\$r4,\\\$r5" } } */
+
+long
+div(long a, long b)
+{
+  return a / b;
+}

gcc/testsuite/gcc.target/loongarch/div-2.c

@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mno-check-zero-division" } */
+/* { dg-final { scan-assembler "div.\[wd\]\t\\\$r4,\\\$r5,\\\$r4" } } */
+
+long
+div(long a, long b)
+{
+  return b / a;
+}

gcc/testsuite/gcc.target/loongarch/div-3.c

@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mcheck-zero-division" } */
+/* { dg-final { scan-assembler-not "div.\[wd\]\t\\\$r4,\\\$r5,\\\$r4" } } */
+
+long
+div(long a, long b)
+{
+  return b / a;
+}