Re: [PATCH, ARM 6/7, ping1] Add support for CB(N)Z and (U|S)DIV to ARMv8-M Baseline

[Thomas Preudhomme <thomas dot preudhomme at foss dot arm dot com>]

On Friday 20 May 2016 14:22:48 Kyrill Tkachov wrote:
> Hi Thomas,
> 

> 
> Hmm, I'm not a fan of this change. arm_print_operand_punct_valid_p is an
> implementation of a target hook that is used to validate user-provided
> inline asm as well and is therefore the right place to reject such invalid
> constructs.
> 
> This is just working around the fact that the output template for the
> [u]divsi3 patterns has a '%?' in it that is illegal in Thumb1 and will not
> be used for ARMv8-M Baseline anyway. I'd prefer it if you add a second
> alternative to those patterns and emit the sdiv/udiv mnemonic without the
> '%?' and enable that for the v8mb arch attribute (and mark the existing
> alternative as requiring the "32" arch attribute).

Fixed.

> 
> s/TARGET_HAVE_MOVT/TARGET_HAVE_CBZ/

Likewise.

> > +  [(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 2))
> > +		 (le (minus (match_dup 2) (pc)) (const_int 128))
> > +		 (not (match_test "which_alternative")))
> 
> This pattern only has one alternative so "which_alternative"
> will always be 0, so the (not (match_test "which_alternative"))
> test inside the 'and' is redundant and can be removed.

Ditto.

Please find updated ChangeLog entries:

*** gcc/ChangeLog ***

2016-05-23  Thomas Preud'homme  <thomas.preudhomme@arm.com>

        * config/arm/arm.h (TARGET_HAVE_CBZ): Define.
        (TARGET_IDIV): Set for all Thumb targets provided they have hardware
        divide feature.
        * config/arm/arm.md (divsi3): New unpredicable alternative for ARMv8-M
        Baseline.  Make initial alternative TARGET_32BIT only.
        (udivsi3): Likewise.
        * config/arm/thumb1.md (thumb1_cbz): New insn.
        * doc/sourcebuild.texi (arm_thumb1_cbz_ok): Document new effective
        target.


*** gcc/testsuite/ChangeLog ***

2016-05-23  Thomas Preud'homme  <thomas.preudhomme@arm.com>

        * lib/target-supports.exp (check_effective_target_arm_thumb1_cbz_ok):
        Add new arm_thumb1_cbz_ok effective target.
        * gcc.target/arm/cbz.c: New test.


Updated patch in attachment.

Best regards,

Thomas

diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index 5f8cfb07a841f7da39cd9e1c2c675dddb807a64f..4b8b7b6b96bdb697a3856ce4f56656b572c6bd22 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -271,9 +271,12 @@ extern void (*arm_lang_output_object_attributes_hook)(void);
 /* Nonzero if this chip provides the MOVW and MOVT instructions.  */
 #define TARGET_HAVE_MOVT	(arm_arch_thumb2 || arm_arch8)
 
+/* Nonzero if this chip provides the CBZ and CBNZ instructions.  */
+#define TARGET_HAVE_CBZ		(arm_arch_thumb2 || arm_arch8)
+
 /* Nonzero if integer division instructions supported.  */
 #define TARGET_IDIV	((TARGET_ARM && arm_arch_arm_hwdiv)	\
-			 || (TARGET_THUMB2 && arm_arch_thumb_hwdiv))
+			 || (TARGET_THUMB && arm_arch_thumb_hwdiv))
 
 /* Nonzero if disallow volatile memory access in IT block.  */
 #define TARGET_NO_VOLATILE_CE		(arm_arch_no_volatile_ce)
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index 3f97c2ad68661e6a0f52ce4fb89f52ab73943a6e..b94c3626d4e82907eb9f81b9d56fc2ea006f9e08 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -4333,23 +4333,29 @@
 
 ;; Division instructions
 (define_insn "divsi3"
-  [(set (match_operand:SI	  0 "s_register_operand" "=r")
-	(div:SI (match_operand:SI 1 "s_register_operand"  "r")
-		(match_operand:SI 2 "s_register_operand"  "r")))]
+  [(set (match_operand:SI	  0 "s_register_operand" "=r,r")
+	(div:SI (match_operand:SI 1 "s_register_operand"  "r,r")
+		(match_operand:SI 2 "s_register_operand"  "r,r")))]
   "TARGET_IDIV"
-  "sdiv%?\t%0, %1, %2"
-  [(set_attr "predicable" "yes")
+  "@
+   sdiv%?\t%0, %1, %2
+   sdiv\t%0, %1, %2"
+  [(set_attr "arch" "32,v8mb")
+   (set_attr "predicable" "yes")
    (set_attr "predicable_short_it" "no")
    (set_attr "type" "sdiv")]
 )
 
 (define_insn "udivsi3"
-  [(set (match_operand:SI	   0 "s_register_operand" "=r")
-	(udiv:SI (match_operand:SI 1 "s_register_operand"  "r")
-		 (match_operand:SI 2 "s_register_operand"  "r")))]
+  [(set (match_operand:SI	   0 "s_register_operand" "=r,r")
+	(udiv:SI (match_operand:SI 1 "s_register_operand"  "r,r")
+		 (match_operand:SI 2 "s_register_operand"  "r,r")))]
   "TARGET_IDIV"
-  "udiv%?\t%0, %1, %2"
-  [(set_attr "predicable" "yes")
+  "@
+   udiv%?\t%0, %1, %2
+   udiv\t%0, %1, %2"
+  [(set_attr "arch" "32,v8mb")
+   (set_attr "predicable" "yes")
    (set_attr "predicable_short_it" "no")
    (set_attr "type" "udiv")]
 )
diff --git a/gcc/config/arm/thumb1.md b/gcc/config/arm/thumb1.md
index 47e569d0c259cd17d86a03061e5b47b3dab4579f..0a8c364cc01aad34849f57879f9f18f9b92851c0 100644
--- a/gcc/config/arm/thumb1.md
+++ b/gcc/config/arm/thumb1.md
@@ -973,6 +973,91 @@
   DONE;
 })
 
+;; A pattern for the CB(N)Z instruction added in ARMv8-M Baseline profile,
+;; adapted from cbranchsi4_insn.  Modifying cbranchsi4_insn instead leads to
+;; code generation difference for ARMv6-M because the minimum length of the
+;; instruction becomes 2 even for ARMv6-M due to a limitation in genattrtab's
+;; handling of PC in the length condition.
+(define_insn "thumb1_cbz"
+  [(set (pc) (if_then_else
+	      (match_operator 0 "equality_operator"
+	       [(match_operand:SI 1 "s_register_operand" "l")
+		(const_int 0)])
+	      (label_ref (match_operand 2 "" ""))
+	      (pc)))]
+  "TARGET_THUMB1 && TARGET_HAVE_CBZ"
+{
+  if (get_attr_length (insn) == 2)
+    {
+      if (GET_CODE (operands[0]) == EQ)
+	return "cbz\t%1, %l2";
+      else
+	return "cbnz\t%1, %l2";
+    }
+  else
+    {
+      rtx t = cfun->machine->thumb1_cc_insn;
+      if (t != NULL_RTX)
+	{
+	  if (!rtx_equal_p (cfun->machine->thumb1_cc_op0, operands[1])
+	      || !rtx_equal_p (cfun->machine->thumb1_cc_op1, operands[2]))
+	    t = NULL_RTX;
+	  if (cfun->machine->thumb1_cc_mode == CC_NOOVmode)
+	    {
+	      if (!noov_comparison_operator (operands[0], VOIDmode))
+		t = NULL_RTX;
+	    }
+	  else if (cfun->machine->thumb1_cc_mode != CCmode)
+	    t = NULL_RTX;
+	}
+      if (t == NULL_RTX)
+	{
+	  output_asm_insn ("cmp\t%1, #0", operands);
+	  cfun->machine->thumb1_cc_insn = insn;
+	  cfun->machine->thumb1_cc_op0 = operands[1];
+	  cfun->machine->thumb1_cc_op1 = operands[2];
+	  cfun->machine->thumb1_cc_mode = CCmode;
+	}
+      else
+	/* Ensure we emit the right type of condition code on the jump.  */
+	XEXP (operands[0], 0) = gen_rtx_REG (cfun->machine->thumb1_cc_mode,
+					     CC_REGNUM);
+
+      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%=:";
+	case 8:  return "b%D0\t.LCB%=;bl\t%l2\t%@far jump\n.LCB%=:";
+	default: gcc_unreachable ();
+	}
+    }
+}
+  [(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 2))
+		 (le (minus (match_dup 2) (pc)) (const_int 128)))
+	    (const_int 2)
+	    (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)))))
+   (set (attr "type")
+	(if_then_else
+	    (eq_attr "length" "2")
+	    (const_string "branch")
+	    (const_string "multiple")))]
+)
+
 (define_insn "cbranchsi4_insn"
   [(set (pc) (if_then_else
 	      (match_operator 0 "arm_comparison_operator"
diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index 1fcd464c27c87ec89d1621a94fe72aa8ae5a5a0a..72a7c020d6d25ffe152d9618281c2be632b57a27 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -1605,6 +1605,10 @@ ARM target prefers @code{LDRD} and @code{STRD} instructions over
 ARM target generates Thumb-1 code for @code{-mthumb} with @code{MOVW}
 and @code{MOVT} instructions available.
 
+@item arm_thumb1_cbz_ok
+ARM target generates Thumb-1 code for @code{-mthumb} with
+@code{CBZ} and @code{CBNZ} instructions available.
+
 @end table
 
 @subsubsection AArch64-specific attributes
diff --git a/gcc/testsuite/gcc.target/arm/cbz.c b/gcc/testsuite/gcc.target/arm/cbz.c
new file mode 100644
index 0000000000000000000000000000000000000000..5d3de6387777743883a3baf66b878a8a0c3f1783
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/cbz.c
@@ -0,0 +1,12 @@
+/* { dg-do compile {target { arm_thumb2 || arm_thumb1_cbz_ok } } } */
+/* { dg-options "-O2" } */
+
+int
+foo (int a, int *b)
+{
+  if (a)
+    *b = 1;
+  return 0;
+}
+
+/* { dg-final { scan-assembler-times "cbz\\tr\\d" 1 } } */
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index b71007e5ebcd925c5c27d58647deee8c53c43600..127af0a1f33bebb0ecc6aa8587d992e89524ce6e 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -3346,6 +3346,23 @@ proc check_effective_target_arm_thumb1_movt_ok {} {
     }
 }
 
+# Return 1 if this is an ARM target where -mthumb causes Thumb-1 to be
+# used and CBZ and CBNZ instructions are available.
+
+proc check_effective_target_arm_thumb1_cbz_ok {} {
+    if [check_effective_target_arm_thumb1_ok] {
+	return [check_no_compiler_messages arm_movt object {
+	    int
+	    foo (void)
+	    {
+	      asm ("cbz r0, 2f\n2:");
+	    }
+	} "-mthumb"]
+    } else {
+	return 0
+    }
+}
+
 # Return 1 if this compilation turns on string_ops_prefer_neon on.
 
 proc check_effective_target_arm_tune_string_ops_prefer_neon { } {