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Re: [PATCH][AArch64][v2] Improve comparison with complex immediates followed by branch/cset

From: Kyrill Tkachov <kyrylo dot tkachov at arm dot com>
To: James Greenhalgh <james dot greenhalgh at arm dot com>
Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Marcus Shawcroft <marcus dot shawcroft at arm dot com>, Richard Earnshaw <Richard dot Earnshaw at arm dot com>
Date: Mon, 23 Nov 2015 10:33:01 +0000
Subject: Re: [PATCH][AArch64][v2] Improve comparison with complex immediates followed by branch/cset
Authentication-results: sourceware.org; auth=none
References: <5638D61C dot 5060100 at arm dot com> <20151112120543 dot GA22716 at arm dot com>


On 12/11/15 12:05, James Greenhalgh wrote:

On Tue, Nov 03, 2015 at 03:43:24PM +0000, Kyrill Tkachov wrote:

Hi all,

Bootstrapped and tested on aarch64.

Ok for trunk?

Comments in-line.


Here's an updated patch according to your comments.
Sorry it took so long to respin it, had other things to deal with with
stage1 closing...

I've indented the sample code sequences and used valid mnemonics.
These patterns can only match during combine, so I'd expect them to always
split during combine or immediately after, but I don't think that's a documented
guarantee so I've gated them on !reload_completed.

I've used IN_RANGE in the predicate.md hunk and added scan-assembler checks
in the tests.

Is this ok?

Thanks,
Kyrill

2015-11-20  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

    * config/aarch64/aarch64.md (*condjump): Rename to...
    (condjump): ... This.
    (*compare_condjump<mode>): New define_insn_and_split.
    (*compare_cstore<mode>_insn): Likewise.
    (*cstore<mode>_insn): Rename to...
    (cstore<mode>_insn): ... This.
    * config/aarch64/iterators.md (CMP): Handle ne code.
    * config/aarch64/predicates.md (aarch64_imm24): New predicate.

2015-11-20  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

    * gcc.target/aarch64/cmpimm_branch_1.c: New test.
    * gcc.target/aarch64/cmpimm_cset_1.c: Likewise.

Thanks,
Kyrill


2015-11-03  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     * config/aarch64/aarch64.md (*condjump): Rename to...
     (condjump): ... This.
     (*compare_condjump<mode>): New define_insn_and_split.
     (*compare_cstore<mode>_insn): Likewise.
     (*cstore<mode>_insn): Rename to...
     (aarch64_cstore<mode>): ... This.
     * config/aarch64/iterators.md (CMP): Handle ne code.
     * config/aarch64/predicates.md (aarch64_imm24): New predicate.

2015-11-03  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     * gcc.target/aarch64/cmpimm_branch_1.c: New test.
     * gcc.target/aarch64/cmpimm_cset_1.c: Likewise.
commit 7df013a391532f39932b80c902e3b4bbd841710f
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Mon Sep 21 10:56:47 2015 +0100

     [AArch64] Improve comparison with complex immediates

diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 126c9c2..1bfc870 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -369,7 +369,7 @@ (define_expand "mod<mode>3"
    }
  )

-(define_insn "*condjump"

+(define_insn "condjump"
    [(set (pc) (if_then_else (match_operator 0 "aarch64_comparison_operator"
  			    [(match_operand 1 "cc_register" "") (const_int 0)])
  			   (label_ref (match_operand 2 "" ""))
@@ -394,6 +394,40 @@ (define_insn "*condjump"
  		      (const_int 1)))]
  )

+;; For a 24-bit immediate CST we can optimize the compare for equality

+;; and branch sequence from:
+;; mov	x0, #imm1
+;; movk	x0, #imm2, lsl 16 /* x0 contains CST.  */
+;; cmp	x1, x0
+;; b<ne,eq> .Label

This would be easier on the eyes if you were to indent the code sequence.

+;; and branch sequence from:
+;;     mov	x0, #imm1
+;;     movk	x0, #imm2, lsl 16 /* x0 contains CST.  */
+;;     cmp	x1, x0
+;;     b<ne,eq> .Label
+;; into the shorter:
+;;     sub	x0, #(CST & 0xfff000)

+;; into the shorter:
+;; sub	x0, #(CST & 0xfff000)
+;; subs	x0, #(CST & 0x000fff)

These instructions are not valid (2 operand sub/subs?) can you write them
out fully for this comment so I can see the data flow?

+;; b<ne,eq> .Label
+(define_insn_and_split "*compare_condjump<mode>"
+  [(set (pc) (if_then_else (EQL
+			      (match_operand:GPI 0 "register_operand" "r")
+			      (match_operand:GPI 1 "aarch64_imm24" "n"))
+			   (label_ref:P (match_operand 2 "" ""))
+			   (pc)))]
+  "!aarch64_move_imm (INTVAL (operands[1]), <MODE>mode)
+   && !aarch64_plus_operand (operands[1], <MODE>mode)"
+  "#"
+  "&& true"
+  [(const_int 0)]
+  {
+    HOST_WIDE_INT lo_imm = UINTVAL (operands[1]) & 0xfff;
+    HOST_WIDE_INT hi_imm = UINTVAL (operands[1]) & 0xfff000;
+    rtx tmp = gen_reg_rtx (<MODE>mode);

Can you guarantee we can always create this pseudo? What if we're a
post-register-allocation split?

+    emit_insn (gen_add<mode>3 (tmp, operands[0], GEN_INT (-hi_imm)));
+    emit_insn (gen_add<mode>3_compare0 (tmp, tmp, GEN_INT (-lo_imm)));
+    rtx cc_reg = gen_rtx_REG (CC_NZmode, CC_REGNUM);
+    rtx cmp_rtx = gen_rtx_fmt_ee (<EQL:CMP>, <MODE>mode, cc_reg, const0_rtx);
+    emit_jump_insn (gen_condjump (cmp_rtx, cc_reg, operands[2]));
+    DONE;
+  }
+)
+
  (define_expand "casesi"
    [(match_operand:SI 0 "register_operand" "")	; Index
     (match_operand:SI 1 "const_int_operand" "")	; Lower bound
@@ -2898,7 +2932,7 @@ (define_expand "cstore<mode>4"
    "
  )

-(define_insn "*cstore<mode>_insn"

+(define_insn "aarch64_cstore<mode>"
    [(set (match_operand:ALLI 0 "register_operand" "=r")
  	(match_operator:ALLI 1 "aarch64_comparison_operator"
  	 [(match_operand 2 "cc_register" "") (const_int 0)]))]
@@ -2907,6 +2941,39 @@ (define_insn "*cstore<mode>_insn"
    [(set_attr "type" "csel")]
  )

+;; For a 24-bit immediate CST we can optimize the compare for equality

+;; and branch sequence from:
+;; mov	x0, #imm1
+;; movk	x0, #imm2, lsl 16 /* x0 contains CST.  */
+;; cmp	x1, x0
+;; cset	x2, <ne,eq>
+;; into the shorter:
+;; sub	x0, #(CST & 0xfff000)
+;; subs	x0, #(CST & 0x000fff)
+;; cset x1, <ne, eq>.

Same comments as above regarding formatting and making this a valid set
of instructions.

+(define_insn_and_split "*compare_cstore<mode>_insn"
+  [(set (match_operand:GPI 0 "register_operand" "=r")
+	 (EQL:GPI (match_operand:GPI 1 "register_operand" "r")
+		  (match_operand:GPI 2 "aarch64_imm24" "n")))]
+  "!aarch64_move_imm (INTVAL (operands[2]), <MODE>mode)
+   && !aarch64_plus_operand (operands[2], <MODE>mode)"
+  "#"
+  "&& true"
+  [(const_int 0)]
+  {
+    HOST_WIDE_INT lo_imm = UINTVAL (operands[2]) & 0xfff;
+    HOST_WIDE_INT hi_imm = UINTVAL (operands[2]) & 0xfff000;
+    rtx tmp = gen_reg_rtx (<MODE>mode);
+    emit_insn (gen_add<mode>3 (tmp, operands[1], GEN_INT (-hi_imm)));
+    emit_insn (gen_add<mode>3_compare0 (tmp, tmp, GEN_INT (-lo_imm)));
+    rtx cc_reg = gen_rtx_REG (CC_NZmode, CC_REGNUM);
+    rtx cmp_rtx = gen_rtx_fmt_ee (<EQL:CMP>, <MODE>mode, cc_reg, const0_rtx);
+    emit_insn (gen_aarch64_cstore<mode> (operands[0], cmp_rtx, cc_reg));
+    DONE;
+  }
+  [(set_attr "type" "csel")]
+)
+
  ;; zero_extend version of the above
  (define_insn "*cstoresi_insn_uxtw"
    [(set (match_operand:DI 0 "register_operand" "=r")
diff --git a/gcc/config/aarch64/iterators.md b/gcc/config/aarch64/iterators.md
index c4a1c98..9f63ef2 100644
--- a/gcc/config/aarch64/iterators.md
+++ b/gcc/config/aarch64/iterators.md
@@ -801,7 +801,7 @@ (define_code_attr cmp_2   [(lt "1") (le "1") (eq "2") (ge "2") (gt "2")
  			   (ltu "1") (leu "1") (geu "2") (gtu "2")])

(define_code_attr CMP [(lt "LT") (le "LE") (eq "EQ") (ge "GE") (gt "GT")

-			   (ltu "LTU") (leu "LEU") (geu "GEU") (gtu "GTU")])
+			   (ltu "LTU") (leu "LEU") (ne "NE") (geu "GEU") (gtu "GTU")])

(define_code_attr fix_trunc_optab [(fix "fix_trunc")

  				   (unsigned_fix "fixuns_trunc")])
diff --git a/gcc/config/aarch64/predicates.md b/gcc/config/aarch64/predicates.md
index 046f852..1bcbf62 100644
--- a/gcc/config/aarch64/predicates.md
+++ b/gcc/config/aarch64/predicates.md
@@ -145,6 +145,11 @@ (define_predicate "aarch64_imm3"
    (and (match_code "const_int")
         (match_test "(unsigned HOST_WIDE_INT) INTVAL (op) <= 4")))

+;; An immediate that fits into 24 bits.

+(define_predicate "aarch64_imm24"
+  (and (match_code "const_int")
+       (match_test "(UINTVAL (op) & 0xffffff) == UINTVAL (op)")))
+

IN_RANGE (UINTVAL (op), 0, 0xffffff) ?

We use quite a few different ways to check an immediate fits in a particular
range in the AArch64 backend, it would be good to pick just one idiomatic
way.

  (define_predicate "aarch64_pwr_imm3"
    (and (match_code "const_int")
         (match_test "INTVAL (op) != 0
diff --git a/gcc/testsuite/gcc.target/aarch64/cmpimm_branch_1.c b/gcc/testsuite/gcc.target/aarch64/cmpimm_branch_1.c
new file mode 100644
index 0000000..d7a8d5b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/cmpimm_branch_1.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-save-temps -O2" } */
+
+/* Test that we emit a sub+subs sequence rather than mov+movk+cmp.  */
+

This just tests that we don't emit cmp, it doesn't test anything else.

+void g (void);
+void
+foo (int x)
+{
+  if (x != 0x123456)
+    g ();
+}
+
+void
+fool (long long x)
+{
+  if (x != 0x123456)
+    g ();
+}
+
+/* { dg-final { scan-assembler-not "cmp\tw\[0-9\]*.*" } } */
+/* { dg-final { scan-assembler-not "cmp\tx\[0-9\]*.*" } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/cmpimm_cset_1.c b/gcc/testsuite/gcc.target/aarch64/cmpimm_cset_1.c
new file mode 100644
index 0000000..619c026
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/cmpimm_cset_1.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-save-temps -O2" } */
+
+/* Test that we emit a sub+subs sequence rather than mov+movk+cmp.  */

Likewise, I don't see any checks for sub/subs.

+
+int
+foo (int x)
+{
+  return x == 0x123456;
+}
+
+long
+fool (long x)
+{
+  return x == 0x123456;
+}
+
+/* { dg-final { scan-assembler-not "cmp\tw\[0-9\]*.*" } } */
+/* { dg-final { scan-assembler-not "cmp\tx\[0-9\]*.*" } } */

Thanks,
James

commit bb44feed4e6beaae25d9bdffa45073dc61c65838
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Mon Sep 21 10:56:47 2015 +0100

    [AArch64] Improve comparison with complex immediates

diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 11f6387..3e57d08 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -372,7 +372,7 @@ (define_expand "mod<mode>3"
   }
 )
 
-(define_insn "*condjump"
+(define_insn "condjump"
   [(set (pc) (if_then_else (match_operator 0 "aarch64_comparison_operator"
 			    [(match_operand 1 "cc_register" "") (const_int 0)])
 			   (label_ref (match_operand 2 "" ""))
@@ -397,6 +397,41 @@ (define_insn "*condjump"
 		      (const_int 1)))]
 )
 
+;; For a 24-bit immediate CST we can optimize the compare for equality
+;; and branch sequence from:
+;; 	mov	x0, #imm1
+;; 	movk	x0, #imm2, lsl 16 /* x0 contains CST.  */
+;; 	cmp	x1, x0
+;; 	b<ne,eq> .Label
+;; into the shorter:
+;; 	sub	x0, x0, #(CST & 0xfff000)
+;; 	subs	x0, x0, #(CST & 0x000fff)
+;; 	b<ne,eq> .Label
+(define_insn_and_split "*compare_condjump<mode>"
+  [(set (pc) (if_then_else (EQL
+			      (match_operand:GPI 0 "register_operand" "r")
+			      (match_operand:GPI 1 "aarch64_imm24" "n"))
+			   (label_ref:P (match_operand 2 "" ""))
+			   (pc)))]
+  "!aarch64_move_imm (INTVAL (operands[1]), <MODE>mode)
+   && !aarch64_plus_operand (operands[1], <MODE>mode)
+   && !reload_completed"
+  "#"
+  "&& true"
+  [(const_int 0)]
+  {
+    HOST_WIDE_INT lo_imm = UINTVAL (operands[1]) & 0xfff;
+    HOST_WIDE_INT hi_imm = UINTVAL (operands[1]) & 0xfff000;
+    rtx tmp = gen_reg_rtx (<MODE>mode);
+    emit_insn (gen_add<mode>3 (tmp, operands[0], GEN_INT (-hi_imm)));
+    emit_insn (gen_add<mode>3_compare0 (tmp, tmp, GEN_INT (-lo_imm)));
+    rtx cc_reg = gen_rtx_REG (CC_NZmode, CC_REGNUM);
+    rtx cmp_rtx = gen_rtx_fmt_ee (<EQL:CMP>, <MODE>mode, cc_reg, const0_rtx);
+    emit_jump_insn (gen_condjump (cmp_rtx, cc_reg, operands[2]));
+    DONE;
+  }
+)
+
 (define_expand "casesi"
   [(match_operand:SI 0 "register_operand" "")	; Index
    (match_operand:SI 1 "const_int_operand" "")	; Lower bound
@@ -2901,7 +2936,7 @@ (define_expand "cstore<mode>4"
   "
 )
 
-(define_insn "*cstore<mode>_insn"
+(define_insn "aarch64_cstore<mode>"
   [(set (match_operand:ALLI 0 "register_operand" "=r")
 	(match_operator:ALLI 1 "aarch64_comparison_operator"
 	 [(match_operand 2 "cc_register" "") (const_int 0)]))]
@@ -2910,6 +2945,40 @@ (define_insn "*cstore<mode>_insn"
   [(set_attr "type" "csel")]
 )
 
+;; For a 24-bit immediate CST we can optimize the compare for equality
+;; and branch sequence from:
+;; 	mov	x0, #imm1
+;; 	movk	x0, #imm2, lsl 16 /* x0 contains CST.  */
+;; 	cmp	x1, x0
+;; 	cset	x2, <ne,eq>
+;; into the shorter:
+;; 	sub	x0, x0, #(CST & 0xfff000)
+;; 	subs	x0, x0, #(CST & 0x000fff)
+;; 	cset x1, <ne, eq>.
+(define_insn_and_split "*compare_cstore<mode>_insn"
+  [(set (match_operand:GPI 0 "register_operand" "=r")
+	 (EQL:GPI (match_operand:GPI 1 "register_operand" "r")
+		  (match_operand:GPI 2 "aarch64_imm24" "n")))]
+  "!aarch64_move_imm (INTVAL (operands[2]), <MODE>mode)
+   && !aarch64_plus_operand (operands[2], <MODE>mode)
+   && !reload_completed"
+  "#"
+  "&& true"
+  [(const_int 0)]
+  {
+    HOST_WIDE_INT lo_imm = UINTVAL (operands[2]) & 0xfff;
+    HOST_WIDE_INT hi_imm = UINTVAL (operands[2]) & 0xfff000;
+    rtx tmp = gen_reg_rtx (<MODE>mode);
+    emit_insn (gen_add<mode>3 (tmp, operands[1], GEN_INT (-hi_imm)));
+    emit_insn (gen_add<mode>3_compare0 (tmp, tmp, GEN_INT (-lo_imm)));
+    rtx cc_reg = gen_rtx_REG (CC_NZmode, CC_REGNUM);
+    rtx cmp_rtx = gen_rtx_fmt_ee (<EQL:CMP>, <MODE>mode, cc_reg, const0_rtx);
+    emit_insn (gen_aarch64_cstore<mode> (operands[0], cmp_rtx, cc_reg));
+    DONE;
+  }
+  [(set_attr "type" "csel")]
+)
+
 ;; zero_extend version of the above
 (define_insn "*cstoresi_insn_uxtw"
   [(set (match_operand:DI 0 "register_operand" "=r")
diff --git a/gcc/config/aarch64/iterators.md b/gcc/config/aarch64/iterators.md
index c2eb7de..422bc87 100644
--- a/gcc/config/aarch64/iterators.md
+++ b/gcc/config/aarch64/iterators.md
@@ -824,7 +824,8 @@ (define_code_attr cmp_2   [(lt "1") (le "1") (eq "2") (ge "2") (gt "2")
 			   (ltu "1") (leu "1") (geu "2") (gtu "2")])
 
 (define_code_attr CMP [(lt "LT") (le "LE") (eq "EQ") (ge "GE") (gt "GT")
-			   (ltu "LTU") (leu "LEU") (geu "GEU") (gtu "GTU")])
+			(ltu "LTU") (leu "LEU") (ne "NE") (geu "GEU")
+			(gtu "GTU")])
 
 (define_code_attr fix_trunc_optab [(fix "fix_trunc")
 				   (unsigned_fix "fixuns_trunc")])
diff --git a/gcc/config/aarch64/predicates.md b/gcc/config/aarch64/predicates.md
index e7f76e0..c0c3ff5 100644
--- a/gcc/config/aarch64/predicates.md
+++ b/gcc/config/aarch64/predicates.md
@@ -145,6 +145,11 @@ (define_predicate "aarch64_imm3"
   (and (match_code "const_int")
        (match_test "(unsigned HOST_WIDE_INT) INTVAL (op) <= 4")))
 
+;; An immediate that fits into 24 bits.
+(define_predicate "aarch64_imm24"
+  (and (match_code "const_int")
+       (match_test "IN_RANGE (UINTVAL (op), 0, 0xffffff)")))
+
 (define_predicate "aarch64_pwr_imm3"
   (and (match_code "const_int")
        (match_test "INTVAL (op) != 0
diff --git a/gcc/testsuite/gcc.target/aarch64/cmpimm_branch_1.c b/gcc/testsuite/gcc.target/aarch64/cmpimm_branch_1.c
new file mode 100644
index 0000000..7ad736b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/cmpimm_branch_1.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-save-temps -O2" } */
+
+/* Test that we emit a sub+subs sequence rather than mov+movk+cmp.  */
+
+void g (void);
+void
+foo (int x)
+{
+  if (x != 0x123456)
+    g ();
+}
+
+void
+fool (long long x)
+{
+  if (x != 0x123456)
+    g ();
+}
+
+/* { dg-final { scan-assembler-not "cmp\tw\[0-9\]*.*" } } */
+/* { dg-final { scan-assembler-not "cmp\tx\[0-9\]*.*" } } */
+/* { dg-final { scan-assembler-times "sub\tw\[0-9\]+.*" 1 } } */
+/* { dg-final { scan-assembler-times "sub\tx\[0-9\]+.*" 1 } } */
+/* { dg-final { scan-assembler-times "subs\tw\[0-9\]+.*" 1 } } */
+/* { dg-final { scan-assembler-times "subs\tx\[0-9\]+.*" 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/cmpimm_cset_1.c b/gcc/testsuite/gcc.target/aarch64/cmpimm_cset_1.c
new file mode 100644
index 0000000..6a03cc9
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/cmpimm_cset_1.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-save-temps -O2" } */
+
+/* Test that we emit a sub+subs sequence rather than mov+movk+cmp.  */
+
+int
+foo (int x)
+{
+  return x == 0x123456;
+}
+
+long
+fool (long x)
+{
+  return x == 0x123456;
+}
+
+/* { dg-final { scan-assembler-not "cmp\tw\[0-9\]*.*" } } */
+/* { dg-final { scan-assembler-not "cmp\tx\[0-9\]*.*" } } */
+/* { dg-final { scan-assembler-times "sub\tw\[0-9\]+.*" 1 } } */
+/* { dg-final { scan-assembler-times "sub\tx\[0-9\]+.*" 1 } } */
+/* { dg-final { scan-assembler-times "subs\tw\[0-9\]+.*" 1 } } */
+/* { dg-final { scan-assembler-times "subs\tx\[0-9\]+.*" 1 } } */

Follow-Ups:
- Re: [PATCH][AArch64][v2] Improve comparison with complex immediates followed by branch/cset
  - From: James Greenhalgh

References:
- [PATCH][AArch64][v2] Improve comparison with complex immediates followed by branch/cset
  - From: Kyrill Tkachov
- Re: [PATCH][AArch64][v2] Improve comparison with complex immediates followed by branch/cset
  - From: James Greenhalgh

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