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cmd/internal/obj/ppc64: generate small, shifted constants in register

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Check for shifted 16b constants, and transform them to avoid the load
penalty. This should be much faster than loading, and reduce binary
size by reducing the constant pool size.

Change-Id: I6834e08be7ca88e3b77449d226d08d199db84299
Reviewed-on: https://go-review.googlesource.com/c/go/+/531119
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Paul Murphy <murp@ibm.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Paul E. Murphy 2023-09-18 17:14:03 -05:00 committed by Paul Murphy
parent e47cab13a5
commit 36ecff0893
3 changed files with 61 additions and 12 deletions
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18
src/cmd/asm/internal/asm/testdata/ppc64.s vendored
View file

@ -32,11 +32,17 @@ TEXT asmtest(SB),DUPOK|NOSPLIT,$0
MOVW $2147483649, R5 // 6405800060a50001 or 0600800038a00001
MOVD $2147483649, R5 // 6405800060a50001 or 0600800038a00001
// Hex constant 0xFFFFFFFF80000001
MOVD $-2147483647, R5 // 3ca0800060a50001 or 0603800038a00001
// Hex constant 0xFFFFFFFE00000000 (load of constant on < power10, pli on >= power10
MOVD $-8589934592, R5 // 3ca00000e8a50000 or 0602000038a00000
// Hex constant 0xFFFFFFFE00000000
ADD $-8589934592, R5 // 3fe0fffe63ff00007bff83e463ff00007cbf2a14 or 0602000038a50000
MOVD $-2147483647, R5 // 3ca0800060a50001 or 0603800038a00001
// Hex constant 0xFFFFFFFE00000002 (load of constant on < power10, pli on >= power10
MOVD $-8589934590, R5 // 3ca00000e8a50000 or 0602000038a00002
// TODO: These are preprocessed by the assembler into MOVD $const>>shift, R5; SLD $shift, R5.
// This only captures the MOVD. Should the SLD be appended to the encoding by the test?
// Hex constant 0x20004000000
MOVD $2199090364416, R5 // 60058001
// Hex constant 0xFFFFFE0004000000
MOVD $-2198956146688, R5 // 38a08001
MOVD 8(R3), R4 // e8830008
MOVD (R3)(R4), R5 // 7ca4182a
MOVD (R3)(R0), R5 // 7ca0182a
@ -168,6 +174,8 @@ TEXT asmtest(SB),DUPOK|NOSPLIT,$0
ADD $-32767, R5, R4 // 38858001
ADD $-32768, R6 // 38c68000
ADD $-32768, R6, R5 // 38a68000
// Hex constant 0xFFFFFFFE00000000
ADD $-8589934592, R5 // 3fe0fffe63ff00007bff83e463ff00007cbf2a14 or 0602000038a50000
//TODO: this compiles to add r5,r6,r0. It should be addi r5,r6,0.
// this is OK since r0 == $0, but the latter is preferred.

30
src/cmd/internal/obj/ppc64/obj9.go
View file

@ -36,6 +36,7 @@ import (
"cmd/internal/sys"
"internal/abi"
"log"
"math/bits"
)
func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
@ -80,19 +81,34 @@ func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
}
case AMOVD:
// 32b constants (signed and unsigned) can be generated via 1 or 2 instructions.
// 32b constants (signed and unsigned) can be generated via 1 or 2 instructions. They can be assembled directly.
isS32 := int64(int32(p.From.Offset)) == p.From.Offset
isU32 := uint64(uint32(p.From.Offset)) == uint64(p.From.Offset)
// If prefixed instructions are supported, a 34b signed constant can be generated by one pli instruction.
isS34 := pfxEnabled && (p.From.Offset<<30)>>30 == p.From.Offset
// If the constant cannot be generated with 2 or less instructions, it must be placed in memory and loaded.
if p.From.Type == obj.TYPE_CONST && p.From.Name == obj.NAME_NONE && p.From.Reg == 0 && !isS32 && !isU32 && !isS34 {
p.From.Type = obj.TYPE_MEM
p.From.Sym = ctxt.Int64Sym(p.From.Offset)
p.From.Name = obj.NAME_EXTERN
p.From.Offset = 0
// Is this a shifted 16b constant? If so, rewrite it to avoid a creating and loading a constant.
val := p.From.Offset
shift := bits.TrailingZeros64(uint64(val))
mask := 0xFFFF << shift
if val&int64(mask) == val || (val>>(shift+16) == -1 && (val>>shift)<<shift == val) {
// Rewrite this value into MOVD $const>>shift, Rto; SLD $shift, Rto
q := obj.Appendp(p, c.newprog)
q.As = ASLD
q.From.Type = obj.TYPE_CONST
q.From.Offset = int64(shift)
q.To = p.To
p.From.Offset >>= shift
p = q
} else {
// Load the constant from memory.
p.From.Type = obj.TYPE_MEM
p.From.Sym = ctxt.Int64Sym(p.From.Offset)
p.From.Name = obj.NAME_EXTERN
p.From.Offset = 0
}
}
}

25
test/codegen/constants.go Normal file
View file

@ -0,0 +1,25 @@
// asmcheck
// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package codegen
func shifted16BitConstants(out [64]uint64) {
// ppc64x: "MOVD\t[$]8193,", "SLD\t[$]27,"
out[0] = 0x0000010008000000
// ppc64x: "MOVD\t[$]-32767", "SLD\t[$]26,"
out[1] = 0xFFFFFE0004000000
// ppc64x: "MOVD\t[$]-1", "SLD\t[$]48,"
out[2] = 0xFFFF000000000000
// ppc64x: "MOVD\t[$]65535", "SLD\t[$]44,"
out[3] = 0x0FFFF00000000000
// ppc64x: "MOVD\t[$]i64.fffff00000000001[(]SB[)]"
out[4] = 0xFFFFF00000000001
// ppc64x: "MOVD\t[$]i64.fffff80000000001[(]SB[)]"
out[5] = 0xFFFFF80000000001
// ppc64x: "MOVD\t[$]i64.0ffff80000000000[(]SB[)]"
out[6] = 0x0FFFF80000000000
}