[PATCH] Add define_insn_and_split for combine to detect x < 123U ? -1 : 0 (PR target/88425)

[Jakub Jelinek]

Hi!

For the following testcase (x < 123U ? -1U : 0) we emit worse code than for
(x < y ? -1U : 0).  That is because the generic code canonicalizes x < 123U
comparisons into x <= 122U.  For this particular case, we want LTU though,
as that sets carry and we can then just sbb.

The following patch adds an insn with splitter for this.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2018-12-11  Jakub Jelinek  <ja...@redhat.com>

        PR target/88425
        * config/i386/i386.md (*x86_mov<SWI48:mode>cc_0_m1_neg_leu<SWI:mode>):
        New define_insn_and_split.

        * gcc.target/i386/pr88425.c: New test.

--- gcc/config/i386/i386.md.jj  2018-11-22 10:40:31.179683319 +0100
+++ gcc/config/i386/i386.md     2018-12-10 11:24:49.785830186 +0100
@@ -17195,6 +17195,24 @@ (define_insn "*x86_mov<mode>cc_0_m1_neg"
    (set_attr "mode" "<MODE>")
    (set_attr "length_immediate" "0")])
 
+(define_insn_and_split "*x86_mov<SWI48:mode>cc_0_m1_neg_leu<SWI:mode>"
+  [(set (match_operand:SWI48 0 "register_operand" "=r")
+       (neg:SWI48
+         (leu:SWI48
+           (match_operand:SWI 1 "nonimmediate_operand" "<SWI:r>m")
+           (match_operand:SWI 2 "<SWI:immediate_operand>" "<SWI:i>"))))
+   (clobber (reg:CC FLAGS_REG))]
+  "CONST_INT_P (operands[2])
+   && INTVAL (operands[2]) != -1
+   && INTVAL (operands[2]) != 2147483647"
+  "#"
+  ""
+  [(set (reg:CC FLAGS_REG) (compare:CC (match_dup 1) (match_dup 2)))
+   (parallel [(set (match_dup 0)
+                  (neg:SWI48 (ltu:SWI48 (reg:CC FLAGS_REG) (const_int 0))))
+             (clobber (reg:CC FLAGS_REG))])]
+  "operands[2] = GEN_INT (INTVAL (operands[2]) + 1);")
+
 (define_insn "*mov<mode>cc_noc"
   [(set (match_operand:SWI248 0 "register_operand" "=r,r")
        (if_then_else:SWI248 (match_operator 1 "ix86_comparison_operator"
--- gcc/testsuite/gcc.target/i386/pr88425.c.jj  2018-12-10 11:31:35.507196453 
+0100
+++ gcc/testsuite/gcc.target/i386/pr88425.c     2018-12-10 11:31:17.231495274 
+0100
@@ -0,0 +1,53 @@
+/* PR target/88425 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -masm=att" } */
+/* { dg-final { scan-assembler-times "sbb\[lq]\[ \t]" 8 } } */
+/* { dg-final { scan-assembler-not "setbe\[ \t]" } } */
+
+unsigned long
+f1 (unsigned long x)
+{
+  return x < 123UL ? -1UL : 0;
+}
+
+unsigned long
+f2 (unsigned int x)
+{
+  return x < 12345U ? -1UL : 0;
+}
+
+unsigned long
+f3 (unsigned short *x)
+{
+  return x[0] < 1234U ? -1UL : 0;
+}
+
+unsigned long
+f4 (unsigned char *x)
+{
+  return x[0] < 123U ? -1UL : 0;
+}
+
+unsigned int
+f5 (unsigned long x)
+{
+  return x < 123UL ? -1U : 0;
+}
+
+unsigned int
+f6 (unsigned int x)
+{
+  return x < 12345U ? -1U : 0;
+}
+
+unsigned int
+f7 (unsigned short *x)
+{
+  return x[0] < 1234U ? -1U : 0;
+}
+
+unsigned int
+f8 (unsigned char *x)
+{
+  return x[0] < 123U ? -1U : 0;
+}

        Jakub