[Bug target/59533] New: [SH] Missed cmp/pz opportunity

[olegendo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59533

            Bug ID: 59533
           Summary: [SH] Missed cmp/pz opportunity
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
            Target: sh*-*-*

In some cases RTL such as

(insn 7 6 8 2 (set (reg:SI 169)
        (not:SI (reg:SI 168))) sh_tmp.cpp:31 -1
     (nil))
(insn 8 7 9 2 (parallel [
            (set (reg:SI 167 [ D.1462+-3 ])
                (lshiftrt:SI (reg:SI 169)
                    (const_int 31 [0x1f])))
            (clobber (reg:SI 147 t))
        ]) sh_tmp.cpp:31 -1
     (nil))

is expanded to refer to the MSB of a word.
In most cases combine can catch such a sequence and generate a cmp/pz insn
(set (reg:SI T_REG) (ge:SI (...) (const_int 0))).  However, in cases where the
extracted MSB is not stored in the T bit, it fails to do so.
Here are a few test functions, compiled with -O2 -m4:

int test0_OK (unsigned char* a)
{
  return a[0] < 128;

/*
        mov.b   @r4,r1
        cmp/pz  r1
        rts
        movt    r0
*/
}

int test1_NG (unsigned char* a, unsigned char* b)
{
  return a[0] + (a[0] < 128);

/*
        mov.b   @r4,r1
        extu.b  r1,r0
        exts.b  r1,r1    // the redundant sign extension is another issue
        not     r1,r1
        shll    r1       // could use 'cmp/pz r1' here.
        mov     #0,r1
        rts
        addc    r1,r0
*/
}

int test2_NG (unsigned char* a, unsigned char* b)
{
  return a[0] + ((a[0] & 0x80) == 0);
/*
        mov.b   @r4,r1
        extu.b  r1,r0
        exts.b  r1,r1    // the redundant sign extension is another issue
        not     r1,r1
        shll    r1       // could use 'cmp/pz r1' here.
        mov     #0,r1
        rts
        addc    r1,r0
*/
}

int test3_OK (unsigned char* a, unsigned char* b)
{
  return a[0] + (a[0] > 127);
/*
        mov.b   @r4,r1
        extu.b  r1,r0
        exts.b  r1,r1
        shll    r1
        mov     #0,r1
        rts
        addc    r1,r0
*/
}

int test4_OK (unsigned char* a, unsigned char* b)
{
  return a[0] + ((a[0] & 0x80) != 0);
/*
        mov.b   @r4,r1
        extu.b  r1,r0
        exts.b  r1,r1
        shll    r1
        mov     #0,r1
        rts
        addc    r1,r0
*/
}

int test5_OK (unsigned char* a, int b, int c)
{
  if (a[0] < 128)
    return c;
  else
    return b + 50;

/*
        mov.b   @r4,r1
        cmp/pz  r1
        bt      .L9
        mov     r5,r6
        add     #50,r6
.L9:
        rts
        mov     r6,r0
*/
}

unsigned int test6_OK (unsigned int a)
{
  return ~a >> 31;

/*
        cmp/pz  r4
        rts
        movt    r0
*/
}


The following patch fixes the issue:

Index: gcc/config/sh/sh.md
===================================================================
--- gcc/config/sh/sh.md    (revision 205971)
+++ gcc/config/sh/sh.md    (working copy)
@@ -4707,13 +4707,28 @@
   DONE;
 })

-(define_insn "shll"
+(define_insn_and_split "shll"
   [(set (match_operand:SI 0 "arith_reg_dest" "=r")
     (ashift:SI (match_operand:SI 1 "arith_reg_operand" "0") (const_int 1)))
    (set (reg:SI T_REG)
     (lt:SI (match_dup 1) (const_int 0)))]
   "TARGET_SH1"
   "shll    %0"
+  "&& can_create_pseudo_p ()"
+  [(set (reg:SI T_REG) (ge:SI (match_dup 2) (const_int 0)))
+   (set (match_dup 0) (plus:SI (match_dup 1) (match_dup 1)))]
+{
+  rtx i = curr_insn;
+  rtx s = find_last_value (operands[1], &i, curr_insn, true);
+
+  if (s == operands[1] || i == curr_insn)
+    FAIL;
+
+  if (GET_CODE (s) == NOT && REG_P (XEXP (s, 0)))
+    operands[2] = XEXP (s, 0);
+  else
+    FAIL;
+}
   [(set_attr "type" "arith")])

 (define_insn "*ashlsi_c_void"