cmd/internal/obj: change Prog.From3 to RestArgs ([]Addr)

This change makes it easier to express instructions
with arbitrary number of operands.

Rationale: previous approach with operand "hiding" does
not scale well, AVX and especially AVX512 have many
instructions with 3+ operands.

x86 asm backend is updated to handle up to 6 explicit operands.
It also fixes issue with 4-th immediate operand type checks.
All `ytab` tables are updated accordingly.

Changes to non-x86 backends only include these patterns:
`p.From3 = X` => `p.SetFrom3(X)`
`p.From3.X = Y` => `p.GetFrom3().X = Y`

Over time, other backends can adapt Prog.RestArgs
and reduce the amount of workarounds.

-- Performance --

x/benchmark/build:

$ benchstat upstream.bench patched.bench
name      old time/op                 new time/op                 delta
Build-48                  21.7s ± 2%                  21.8s ± 2%   ~     (p=0.218 n=10+10)

name      old binary-size             new binary-size             delta
Build-48                  10.3M ± 0%                  10.3M ± 0%   ~     (all equal)

name      old build-time/op           new build-time/op           delta
Build-48                  21.7s ± 2%                  21.8s ± 2%   ~     (p=0.218 n=10+10)

name      old build-peak-RSS-bytes    new build-peak-RSS-bytes    delta
Build-48                  145MB ± 5%                  148MB ± 5%   ~     (p=0.218 n=10+10)

name      old build-user+sys-time/op  new build-user+sys-time/op  delta
Build-48                  21.0s ± 2%                  21.2s ± 2%   ~     (p=0.075 n=10+10)

Microbenchmark shows a slight slowdown.

name        old time/op  new time/op  delta
AMD64asm-4  49.5ms ± 1%  49.9ms ± 1%  +0.67%  (p=0.001 n=23+15)

func BenchmarkAMD64asm(b *testing.B) {
  for i := 0; i < b.N; i++ {
    TestAMD64EndToEnd(nil)
    TestAMD64Encoder(nil)
  }
}

Change-Id: I4f1d37b5c2c966da3f2127705ccac9bff0038183
Reviewed-on: https://go-review.googlesource.com/63490
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

2 files changed, 5 insertions, 5 deletions

diff --git a/src/cmd/internal/obj/arm/asm5.go b/src/cmd/internal/obj/arm/asm5.go
index 98b45feb60..479005f294 100644
--- a/src/cmd/internal/obj/arm/asm5.go
+++ b/src/cmd/internal/obj/arm/asm5.go
@@ -2068,11 +2068,11 @@ func (c *ctxt5) asmout(p *obj.Prog, o *Optab, out []uint32) {
 		if r == 0 {
 			r = rt
 		}
-		if p.From3 == nil || p.From3.Type != obj.TYPE_CONST {
+		if p.GetFrom3() == nil || p.GetFrom3().Type != obj.TYPE_CONST {
 			c.ctxt.Diag("%v: missing or wrong LSB", p)
 			break
 		}
-		lsb := p.From3.Offset
+		lsb := p.GetFrom3().Offset
 		width := p.From.Offset
 		if lsb < 0 || lsb > 31 || width <= 0 || (lsb+width) > 31 {
 			c.ctxt.Diag("%v: wrong width or LSB", p)
@@ -3310,8 +3310,8 @@ func (c *ctxt5) chipfloat5(e float64) int {
 func nocache(p *obj.Prog) {
 	p.Optab = 0
 	p.From.Class = 0
-	if p.From3 != nil {
-		p.From3.Class = 0
+	if p.GetFrom3() != nil {
+		p.GetFrom3().Class = 0
 	}
 	p.To.Class = 0
 }
diff --git a/src/cmd/internal/obj/arm/obj5.go b/src/cmd/internal/obj/arm/obj5.go
index 32c4643166..59f044ec9d 100644
--- a/src/cmd/internal/obj/arm/obj5.go
+++ b/src/cmd/internal/obj/arm/obj5.go
@@ -186,7 +186,7 @@ func (c *ctxt5) rewriteToUseGot(p *obj.Prog) {
 			p.From.Offset = 0
 		}
 	}
-	if p.From3 != nil && p.From3.Name == obj.NAME_EXTERN {
+	if p.GetFrom3() != nil && p.GetFrom3().Name == obj.NAME_EXTERN {
 		c.ctxt.Diag("don't know how to handle %v with -dynlink", p)
 	}
 	var source *obj.Addr