xtensa: Small improvement to "*btrue_INT_MIN"

This patch changes the implementation of the insn to test whether the
result itself is negative or not, rather than the MSB of the result of
the ABS machine instruction.  This eliminates the need to consider bit-
endianness and allows for longer branch distances.

     /* example */
     extern void foo(int);
     void test0(int a) {
       if (a == -2147483648)
         foo(a);
     }
     void test1(int a) {
       if (a != -2147483648)
         foo(a);
     }

     ;; before (endianness: little)
     test0:
     	entry	sp, 32
     	abs	a8, a2
     	bbci	a8, 31, .L1
     	mov.n	a10, a2
     	call8	foo
     .L1:
     	retw.n
     test1:
     	entry	sp, 32
     	abs	a8, a2
     	bbsi	a8, 31, .L4
     	mov.n	a10, a2
     	call8	foo
     .L4:
     	retw.n

     ;; after (endianness-independent)
     test0:
     	entry	sp, 32
     	abs	a8, a2
     	bgez	a8, .L1
     	mov.n	a10, a2
     	call8	foo
     .L1:
     	retw.n
     test1:
     	entry	sp, 32
     	abs	a8, a2
     	bltz	a8, .L4
     	mov.n	a10, a2
     	call8	foo
     .L4:
     	retw.n

gcc/ChangeLog:

	* config/xtensa/xtensa.md (*btrue_INT_MIN):
	Change the branch insn condition to test for a negative number
	rather than testing for the MSB.

diff --git a/gcc/config/xtensa/xtensa.md b/gcc/config/xtensa/xtensa.md
index 629dfdde33cb09ca7fc8842f7cddcf5602916cf6..f38fe6da8e483d61ce9600c97e348a66099d7295 100644 (file)
--- a/gcc/config/xtensa/xtensa.md
+++ b/gcc/config/xtensa/xtensa.md
@@ -2024,26 +2024,23 @@
                        [(match_operand:SI 0 "register_operand" "r")
                         (const_int -2147483648)])
                      (label_ref (match_operand 1 ""))
-                     (pc)))]
+                     (pc)))
+   (clobber (match_scratch:SI 3 "=a"))]
   "TARGET_ABS"
   "#"
-  "&& can_create_pseudo_p ()"
+  "&& 1"
   [(set (match_dup 3)
        (abs:SI (match_dup 0)))
    (set (pc)
        (if_then_else (match_op_dup 2
-                       [(zero_extract:SI (match_dup 3)
-                                         (const_int 1)
-                                         (match_dup 4))
+                       [(match_dup 3)
                         (const_int 0)])
                      (label_ref (match_dup 1))
                      (pc)))]
 {
-  operands[3] = gen_reg_rtx (SImode);
-  operands[4] = GEN_INT (BITS_BIG_ENDIAN ? 0 : 31);
-  operands[2] = gen_rtx_fmt_ee (reverse_condition (GET_CODE (operands[2])),
-                               VOIDmode, XEXP (operands[2], 0),
-                               const0_rtx);
+  if (GET_CODE (operands[3]) == SCRATCH)
+    operands[3] = gen_reg_rtx (SImode);
+  PUT_CODE (operands[2], GET_CODE (operands[2]) == EQ ? LT : GE);
 }
   [(set_attr "type"    "jump")
    (set_attr "mode"    "none")