[RFA, ARM] Streamline thumb2 DImode compares

[Richard Henderson]

I noticed this while testing my atomic optabs patch with -mthumb.
This is identical to what we actually output in the current sync code:

>       arm_output_asm_insn (emit, 0, operands, "cmp\t%%0, %%1");
>       if (is_di)
>         {
>           arm_output_it (emit, "", "eq");
>           arm_output_op2 (emit, "cmpeq", old_value_hi, required_value_hi);
>         }

except now it's applicable to all DImode comparisons everywhere.

Bootstrapped with -march=armv7-a -mthumb.  

The only question I have is, can we assume a universal syntax assembler,
or should the output pattern be changed to

  {
    if (TARGET_THUMB)
      return "cmp\t%R0, %R1\;it eq\;cmpeq\t%Q0, %Q1";
    else
      return "cmp\t%R0, %R1\;cmpeq\t%Q0, %Q1";
  }

?


r~

commit c1181684567b75719d3599891f0e650cee51d573
Author: Richard Henderson <r...@redhat.com>
Date:   Thu Dec 15 12:02:03 2011 -0800

    arm: Use arm_cmpdi_unsigned for thumb2 as well
    
    This changes code generation from "eors; eors; orrs" (which ranges
    from 6 to 12 bytes and requires three scratch registers), to
    "cmp; it; cmp" (which is always 6 bytes for register inputs and
    requires no scratch registers).

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index f829a83..18dabda 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -11606,7 +11606,7 @@ arm_select_cc_mode (enum rtx_code op, rtx x, rtx y)
            return CC_Zmode;
 
          /* We can do an equality test in three Thumb instructions.  */
-         if (!TARGET_ARM)
+         if (!TARGET_32BIT)
            return CC_Zmode;
 
          /* FALLTHROUGH */
@@ -11618,7 +11618,7 @@ arm_select_cc_mode (enum rtx_code op, rtx x, rtx y)
          /* DImode unsigned comparisons can be implemented by cmp +
             cmpeq without a scratch register.  Not worth doing in
             Thumb-2.  */
-         if (TARGET_ARM)
+         if (TARGET_32BIT)
            return CC_CZmode;
 
          /* FALLTHROUGH */
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index 937a009..4ec300a 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -7529,8 +7529,8 @@
   [(set (reg:CC_CZ CC_REGNUM)
        (compare:CC_CZ (match_operand:DI 0 "s_register_operand" "r")
                       (match_operand:DI 1 "arm_di_operand"     "rDi")))]
-  "TARGET_ARM"
-  "cmp%?\\t%R0, %R1\;cmpeq\\t%Q0, %Q1"
+  "TARGET_32BIT"
+  "cmp\\t%R0, %R1\;it eq\;cmpeq\\t%Q0, %Q1"
   [(set_attr "conds" "set")
    (set_attr "length" "8")]
 )