diff mbox

[AArch64] Improve comparison with complex immediates followed by branch/cset

Message ID 56162F33.6060103@arm.com
State Superseded
Headers show

Commit Message

Kyrylo Tkachov Oct. 8, 2015, 8:54 a.m. UTC 
Hi all,

This patch slightly improves sequences where we want to compare against a complex immediate and branch against the result
or perform a cset on it.
This means transforming sequences of mov+movk+cmp+branch into sub+subs+branch.
Similar for cset. Unfortunately I can't just do this by simply matching a (compare (reg) (const_int)) rtx because
this transformation is only valid for equal/not equal comparisons, not greater than/less than ones but the compare instruction
pattern only has the general CC mode. We need to also match the use of the condition code.

I've done this by creating a splitter for the conditional jump where the condition is the comparison between the register
and the complex immediate and splitting it into the sub+subs+condjump sequence. Similar for the cstore pattern.
Thankfully we don't split immediate moves until later in the optimization pipeline so combine can still try the right patterns.
With this patch for the example code:
void g(void);
void f8(int x)
{
    if (x != 0x123456) g();
}

I get:
f8:
         sub     w0, w0, #1191936
         subs    w0, w0, #1110
         beq     .L1
         b       g
         .p2align 3
.L1:
         ret

instead of the previous:
f8:
         mov     w1, 13398
         movk    w1, 0x12, lsl 16
         cmp     w0, w1
         beq     .L1
         b       g
         .p2align 3
.L1:
         ret


The condjump case triggered 130 times across all of SPEC2006 which is, admittedly, not much
whereas the cstore case didn't trigger at all. However, the included testcase in the patch
demonstrates the kind of code that it would trigger on.

Bootstrapped and tested on aarch64.

Ok for trunk?

Thanks,
Kyrill


2015-10-08  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.

2015-10-08  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

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

Comments

Kyrylo Tkachov Oct. 13, 2015, 8:21 a.m. UTC | #1 
On 08/10/15 09:54, Kyrill Tkachov wrote:
> Hi all,
>
> This patch slightly improves sequences where we want to compare against a complex immediate and branch against the result
> or perform a cset on it.
> This means transforming sequences of mov+movk+cmp+branch into sub+subs+branch.
> Similar for cset. Unfortunately I can't just do this by simply matching a (compare (reg) (const_int)) rtx because
> this transformation is only valid for equal/not equal comparisons, not greater than/less than ones but the compare instruction
> pattern only has the general CC mode. We need to also match the use of the condition code.
>
> I've done this by creating a splitter for the conditional jump where the condition is the comparison between the register
> and the complex immediate and splitting it into the sub+subs+condjump sequence. Similar for the cstore pattern.
> Thankfully we don't split immediate moves until later in the optimization pipeline so combine can still try the right patterns.
> With this patch for the example code:
> void g(void);
> void f8(int x)
> {
>      if (x != 0x123456) g();
> }
>
> I get:
> f8:
>           sub     w0, w0, #1191936
>           subs    w0, w0, #1110
>           beq     .L1
>           b       g
>           .p2align 3
> .L1:
>           ret
>
> instead of the previous:
> f8:
>           mov     w1, 13398
>           movk    w1, 0x12, lsl 16
>           cmp     w0, w1
>           beq     .L1
>           b       g
>           .p2align 3
> .L1:
>           ret
>
>
> The condjump case triggered 130 times across all of SPEC2006 which is, admittedly, not much
> whereas the cstore case didn't trigger at all. However, the included testcase in the patch
> demonstrates the kind of code that it would trigger on.
>
> Bootstrapped and tested on aarch64.
>
> Ok for trunk?

There's a few changes I'd like to make to this patch and I'll post an updated version when it's ready.
So no need to review this version, besides getting the general idea of the transformation...

Sorry for the noise,
Kyrill


> Thanks,
> Kyrill
>
>
> 2015-10-08  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.
>
> 2015-10-08  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>
>       * gcc.target/aarch64/cmpimm_branch_1.c: New test.
>       * gcc.target/aarch64/cmpimm_cset_1.c: Likewise.
diff mbox

Patch

commit 0c1530fab4c3979fb287f3b960f110e857df79b6
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 83ea74a..acda64f 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 +394,42 @@  (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, #(CST & 0xfff000)
+;; subs	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:DI (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);
+    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
@@ -2894,7 +2930,7 @@  (define_expand "cstore<mode>4"
   "
 )
 
-(define_insn "*cstore<mode>_insn"
+(define_insn "cstore<mode>_insn"
   [(set (match_operand:ALLI 0 "register_operand" "=r")
 	(match_operator:ALLI 1 "aarch64_comparison_operator"
 	 [(match_operand 2 "cc_register" "") (const_int 0)]))]
@@ -2903,6 +2939,39 @@  (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>.
+(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_cstore<mode>_insn (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 a1436ac..8b2663b 100644
--- a/gcc/config/aarch64/iterators.md
+++ b/gcc/config/aarch64/iterators.md
@@ -798,7 +798,7 @@  (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 7b852a4..1b62432 100644
--- a/gcc/config/aarch64/predicates.md
+++ b/gcc/config/aarch64/predicates.md
@@ -138,6 +138,11 @@  (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)")))
+
 (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.  */
+
+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.  */
+
+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\[0-9\]*.*" } } */