diff mbox

ARM patch: New cbranchqi, cbranchhi patterns for Thumb-1

Message ID 4C3F0C1F.6020901@codesourcery.com
State New
Headers show

Commit Message

Bernd Schmidt July 15, 2010, 1:24 p.m. UTC 
On Thumb-1, comparisons of integer values smaller than a word can be
done by shifting the value to the left.  This patch adds a new macroized
pattern, cbranch<mode>4_insn, which is used for QImode and HImode, and
does exactly that.  Effects:

-       lsl     r2, r1, #24
-       lsr     r2, r2, #24
-       cmp     r2, #0
+       lsl     r1, #24
        bne     .L195

This uses the neat trick of putting a matching constraint on a
match_scratch.

An earlier version (with slightly more stupid code) was regression
tested on qemu/arm-linux with my usual set of three flags.  This version
generates identical code as the tested one for all my testcases.  Ok if
retest passes?


Bernd
* config/arm/arm.md (QHI): New define_mode_iterator.
	(cbranch<mode>4_insn): New pattern.

Comments

Richard Earnshaw July 15, 2010, 2:43 p.m. UTC | #1 
On Thu, 2010-07-15 at 15:24 +0200, Bernd Schmidt wrote:
> On Thumb-1, comparisons of integer values smaller than a word can be
> done by shifting the value to the left.  This patch adds a new macroized
> pattern, cbranch<mode>4_insn, which is used for QImode and HImode, and
> does exactly that.  Effects:
> 
> -       lsl     r2, r1, #24
> -       lsr     r2, r2, #24
> -       cmp     r2, #0
> +       lsl     r1, #24
>         bne     .L195
> 
> This uses the neat trick of putting a matching constraint on a
> match_scratch.
> 
> An earlier version (with slightly more stupid code) was regression
> tested on qemu/arm-linux with my usual set of three flags.  This version
> generates identical code as the tested one for all my testcases.  Ok if
> retest passes?
> 
> 
> Bernd

This is going to only set the N and Z flags correctly.  V and C will
have different values.   Having looked at arm_select_cc_mode I can't
quite convince myself that it will be safe for inequality comparisons.
The only relevent test in that that I can see is

  if (GET_MODE (x) == QImode && (op == EQ || op == NE))
    return CC_Zmode;

Which handles your example, but none of the others.

Also note, the same trick should be usable on ARM and Thumb2 if we don't
do that already.

R.
diff mbox

Patch

Index: config/arm/arm.md
===================================================================
--- config/arm/arm.md	(revision 162146)
+++ config/arm/arm.md	(working copy)
@@ -393,6 +393,9 @@  (define_mode_iterator ANY64 [DI DF V8QI 
 ;; The integer modes up to word size
 (define_mode_iterator QHSI [QI HI SI])
 
+;; The integer modes below word size
+(define_mode_iterator QHI [QI HI])
+
 ;;---------------------------------------------------------------------------
 ;; Predicates
 
@@ -6686,6 +6689,43 @@  (define_insn "cbranchsi4_insn"
 		(const_int 8))))]
 )
 
+(define_mode_attr mode_lshift [(QI "24") (HI "16")])
+
+(define_insn "cbranch<mode>4_insn"
+  [(set (pc) (if_then_else
+	      (match_operator 0 "arm_comparison_operator"
+	       [(match_operand:QHI 1 "s_register_operand" "l")
+	        (const_int 0)])
+	      (label_ref (match_operand 2 "" ""))
+	      (pc)))
+   (clobber (match_scratch:QHI 3 "=1"))]
+  "TARGET_THUMB1"
+{
+  output_asm_insn ("lsl\t%1, #<mode_lshift>", operands);
+
+  switch (get_attr_length (insn))
+    {
+    case 4:  return "b%d0\t%l2";
+    case 6:  return "b%D0\t.LCB%=\;b\t%l2\t%@long jump\n.LCB%=:";
+    default: return "b%D0\t.LCB%=\;bl\t%l2\t%@far jump\n.LCB%=:";
+    }
+}
+  [(set (attr "far_jump")
+        (if_then_else
+	    (eq_attr "length" "8")
+	    (const_string "yes")
+            (const_string "no")))
+   (set (attr "length")
+        (if_then_else
+	    (and (ge (minus (match_dup 2) (pc)) (const_int -250))
+	         (le (minus (match_dup 2) (pc)) (const_int 256)))
+	    (const_int 4)
+	    (if_then_else
+	        (and (ge (minus (match_dup 2) (pc)) (const_int -2040))
+		     (le (minus (match_dup 2) (pc)) (const_int 2048)))
+		(const_int 6)
+		(const_int 8))))])
+
 (define_insn "cbranchsi4_scratch"
   [(set (pc) (if_then_else
 	      (match_operator 4 "arm_comparison_operator"