cmd/asm: add s390x branch-on-count instructions
The branch-on-count instructions on s390x decrement the input
register and then compare its value to 0. If not equal the branch
is taken.
These instructions are useful for implementing loops with a set
number of iterations (which might be in a register).
For example, this for loop:
for i := 0; i < n; i++ {
... // i is not used or modified in the loop
}
Could be implemented using this assembly:
MOVD Rn, Ri
loop:
...
BRCTG Ri, loop
Note that i will count down from n in the assembly whereas in the
original for loop it counted up to n which is why we can't use i
in the loop.
These instructions will only be used in hand-written codegen and
assembly for now since SSA blocks cannot currently modify values.
We could look into this in the future though.
Change-Id: Iaab93b8aa2699513b825439b8ea20d8fe2ea1ee6
Reviewed-on: https://go-review.googlesource.com/c/go/+/199977
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
diff --git a/src/cmd/asm/internal/arch/s390x.go b/src/cmd/asm/internal/arch/s390x.go
index 6efae26..0a4d278 100644
--- a/src/cmd/asm/internal/arch/s390x.go
+++ b/src/cmd/asm/internal/arch/s390x.go
@@ -30,6 +30,8 @@
"BR",
"BVC",
"BVS",
+ "BRCT",
+ "BRCTG",
"CMPBEQ",
"CMPBGE",
"CMPBGT",
diff --git a/src/cmd/asm/internal/asm/testdata/s390x.s b/src/cmd/asm/internal/asm/testdata/s390x.s
index 6888651..bc0a49c 100644
--- a/src/cmd/asm/internal/asm/testdata/s390x.s
+++ b/src/cmd/asm/internal/asm/testdata/s390x.s
@@ -266,6 +266,9 @@
BLTU 0(PC) // a7540000
BLEU 0(PC) // a7d40000
+ BRCT R1, 0(PC) // a7160000
+ BRCTG R2, 0(PC) // a7270000
+
CMPBNE R1, R2, 0(PC) // ec1200007064
CMPBEQ R3, R4, 0(PC) // ec3400008064
CMPBLT R5, R6, 0(PC) // ec5600004064
diff --git a/src/cmd/compile/internal/s390x/ggen.go b/src/cmd/compile/internal/s390x/ggen.go
index ae9965c..16af190 100644
--- a/src/cmd/compile/internal/s390x/ggen.go
+++ b/src/cmd/compile/internal/s390x/ggen.go
@@ -38,18 +38,14 @@
// Generate a loop of large clears.
if cnt > clearLoopCutoff {
- n := cnt - (cnt % 256)
- end := int16(s390x.REGRT2)
- p = pp.Appendpp(p, s390x.AADD, obj.TYPE_CONST, 0, off+n, obj.TYPE_REG, end, 0)
- p.Reg = reg
+ ireg := int16(s390x.REGRT2) // register holds number of remaining loop iterations
+ p = pp.Appendpp(p, s390x.AMOVD, obj.TYPE_CONST, 0, cnt/256, obj.TYPE_REG, ireg, 0)
p = pp.Appendpp(p, s390x.ACLEAR, obj.TYPE_CONST, 0, 256, obj.TYPE_MEM, reg, off)
pl := p
p = pp.Appendpp(p, s390x.AADD, obj.TYPE_CONST, 0, 256, obj.TYPE_REG, reg, 0)
- p = pp.Appendpp(p, s390x.ACMP, obj.TYPE_REG, reg, 0, obj.TYPE_REG, end, 0)
- p = pp.Appendpp(p, s390x.ABNE, obj.TYPE_NONE, 0, 0, obj.TYPE_BRANCH, 0, 0)
+ p = pp.Appendpp(p, s390x.ABRCTG, obj.TYPE_REG, ireg, 0, obj.TYPE_BRANCH, 0, 0)
gc.Patch(p, pl)
-
- cnt -= n
+ cnt = cnt % 256
}
// Generate remaining clear instructions without a loop.
diff --git a/src/cmd/internal/obj/s390x/a.out.go b/src/cmd/internal/obj/s390x/a.out.go
index b44531c..7dcf3e8 100644
--- a/src/cmd/internal/obj/s390x/a.out.go
+++ b/src/cmd/internal/obj/s390x/a.out.go
@@ -409,6 +409,10 @@
ABVS
ASYSCALL
+ // branch on count
+ ABRCT
+ ABRCTG
+
// compare and branch
ACRJ
ACGRJ
diff --git a/src/cmd/internal/obj/s390x/anames.go b/src/cmd/internal/obj/s390x/anames.go
index dad710b..c3a76a0 100644
--- a/src/cmd/internal/obj/s390x/anames.go
+++ b/src/cmd/internal/obj/s390x/anames.go
@@ -155,6 +155,8 @@
"BVC",
"BVS",
"SYSCALL",
+ "BRCT",
+ "BRCTG",
"CRJ",
"CGRJ",
"CLRJ",
diff --git a/src/cmd/internal/obj/s390x/asmz.go b/src/cmd/internal/obj/s390x/asmz.go
index ea254c7..3cc7d0b 100644
--- a/src/cmd/internal/obj/s390x/asmz.go
+++ b/src/cmd/internal/obj/s390x/asmz.go
@@ -256,6 +256,10 @@
{i: 90, as: ACLGIJ, a1: C_SCON, a2: C_REG, a3: C_ADDCON, a6: C_SBRA},
{i: 90, as: ACMPUBEQ, a1: C_REG, a3: C_ANDCON, a6: C_SBRA},
+ // branch on count
+ {i: 41, as: ABRCT, a1: C_REG, a6: C_SBRA},
+ {i: 41, as: ABRCTG, a1: C_REG, a6: C_SBRA},
+
// move on condition
{i: 17, as: AMOVDEQ, a1: C_REG, a6: C_REG},
@@ -3394,6 +3398,21 @@
*asm = append(*asm, uint8(wd))
}
+ case 41: // branch on count
+ r1 := p.From.Reg
+ ri2 := (p.Pcond.Pc - p.Pc) >> 1
+ if int64(int16(ri2)) != ri2 {
+ c.ctxt.Diag("branch target too far away")
+ }
+ var opcode uint32
+ switch p.As {
+ case ABRCT:
+ opcode = op_BRCT
+ case ABRCTG:
+ opcode = op_BRCTG
+ }
+ zRI(opcode, uint32(r1), uint32(ri2), asm)
+
case 47: // negate [reg] reg
r := p.From.Reg
if r == 0 {
