cmd/compile: allow conversion from slice to array ptr

Panic if the slice is too short.

Updates #395

Change-Id: I90f4bff2da5d8f3148ba06d2482084f32b25c29a
Reviewed-on: https://go-review.googlesource.com/c/go/+/301650
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

4 files changed, 140 insertions, 136 deletions

diff --git a/src/cmd/compile/internal/ir/expr.go b/src/cmd/compile/internal/ir/expr.go
index 112d3941ce..a9f8c6eae5 100644
--- a/src/cmd/compile/internal/ir/expr.go
+++ b/src/cmd/compile/internal/ir/expr.go
@@ -277,7 +277,7 @@ func (n *ConvExpr) SetOp(op Op) {
 	switch op {
 	default:
 		panic(n.no("SetOp " + op.String()))
-	case OCONV, OCONVIFACE, OCONVNOP, OBYTES2STR, OBYTES2STRTMP, ORUNES2STR, OSTR2BYTES, OSTR2BYTESTMP, OSTR2RUNES, ORUNESTR:
+	case OCONV, OCONVIFACE, OCONVNOP, OBYTES2STR, OBYTES2STRTMP, ORUNES2STR, OSTR2BYTES, OSTR2BYTESTMP, OSTR2RUNES, ORUNESTR, OSLICE2ARRPTR:
 		n.op = op
 	}
 }
diff --git a/src/cmd/compile/internal/ir/fmt.go b/src/cmd/compile/internal/ir/fmt.go
index 1a05079dac..8eb1cffc59 100644
--- a/src/cmd/compile/internal/ir/fmt.go
+++ b/src/cmd/compile/internal/ir/fmt.go
@@ -206,6 +206,7 @@ var OpPrec = []int{
 	OPRINT:         8,
 	ORUNESTR:       8,
 	OSIZEOF:        8,
+	OSLICE2ARRPTR:  8,
 	OSTR2BYTES:     8,
 	OSTR2RUNES:     8,
 	OSTRUCTLIT:     8,
@@ -804,7 +805,8 @@ func exprFmt(n Node, s fmt.State, prec int) {
 		ORUNES2STR,
 		OSTR2BYTES,
 		OSTR2RUNES,
-		ORUNESTR:
+		ORUNESTR,
+		OSLICE2ARRPTR:
 		n := n.(*ConvExpr)
 		if n.Type() == nil || n.Type().Sym() == nil {
 			fmt.Fprintf(s, "(%v)", n.Type())
diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
index b6be74296f..b4db79e5c2 100644
--- a/src/cmd/compile/internal/ir/node.go
+++ b/src/cmd/compile/internal/ir/node.go
@@ -137,6 +137,7 @@ const (
 	OSTR2BYTES    // Type(Left) (Type is []byte, Left is a string)
 	OSTR2BYTESTMP // Type(Left) (Type is []byte, Left is a string, ephemeral)
 	OSTR2RUNES    // Type(Left) (Type is []rune, Left is a string)
+	OSLICE2ARRPTR // Type(Left) (Type is *[N]T, Left is a []T)
 	// Left = Right or (if Colas=true) Left := Right
 	// If Colas, then Ninit includes a DCL node for Left.
 	OAS
diff --git a/src/cmd/compile/internal/ir/op_string.go b/src/cmd/compile/internal/ir/op_string.go
index cfd36c7b3d..156ffd69ba 100644
--- a/src/cmd/compile/internal/ir/op_string.go
+++ b/src/cmd/compile/internal/ir/op_string.go
@@ -29,143 +29,144 @@ func _() {
 	_ = x[OSTR2BYTES-18]
 	_ = x[OSTR2BYTESTMP-19]
 	_ = x[OSTR2RUNES-20]
-	_ = x[OAS-21]
-	_ = x[OAS2-22]
-	_ = x[OAS2DOTTYPE-23]
-	_ = x[OAS2FUNC-24]
-	_ = x[OAS2MAPR-25]
-	_ = x[OAS2RECV-26]
-	_ = x[OASOP-27]
-	_ = x[OCALL-28]
-	_ = x[OCALLFUNC-29]
-	_ = x[OCALLMETH-30]
-	_ = x[OCALLINTER-31]
-	_ = x[OCALLPART-32]
-	_ = x[OCAP-33]
-	_ = x[OCLOSE-34]
-	_ = x[OCLOSURE-35]
-	_ = x[OCOMPLIT-36]
-	_ = x[OMAPLIT-37]
-	_ = x[OSTRUCTLIT-38]
-	_ = x[OARRAYLIT-39]
-	_ = x[OSLICELIT-40]
-	_ = x[OPTRLIT-41]
-	_ = x[OCONV-42]
-	_ = x[OCONVIFACE-43]
-	_ = x[OCONVNOP-44]
-	_ = x[OCOPY-45]
-	_ = x[ODCL-46]
-	_ = x[ODCLFUNC-47]
-	_ = x[ODCLCONST-48]
-	_ = x[ODCLTYPE-49]
-	_ = x[ODELETE-50]
-	_ = x[ODOT-51]
-	_ = x[ODOTPTR-52]
-	_ = x[ODOTMETH-53]
-	_ = x[ODOTINTER-54]
-	_ = x[OXDOT-55]
-	_ = x[ODOTTYPE-56]
-	_ = x[ODOTTYPE2-57]
-	_ = x[OEQ-58]
-	_ = x[ONE-59]
-	_ = x[OLT-60]
-	_ = x[OLE-61]
-	_ = x[OGE-62]
-	_ = x[OGT-63]
-	_ = x[ODEREF-64]
-	_ = x[OINDEX-65]
-	_ = x[OINDEXMAP-66]
-	_ = x[OKEY-67]
-	_ = x[OSTRUCTKEY-68]
-	_ = x[OLEN-69]
-	_ = x[OMAKE-70]
-	_ = x[OMAKECHAN-71]
-	_ = x[OMAKEMAP-72]
-	_ = x[OMAKESLICE-73]
-	_ = x[OMAKESLICECOPY-74]
-	_ = x[OMUL-75]
-	_ = x[ODIV-76]
-	_ = x[OMOD-77]
-	_ = x[OLSH-78]
-	_ = x[ORSH-79]
-	_ = x[OAND-80]
-	_ = x[OANDNOT-81]
-	_ = x[ONEW-82]
-	_ = x[ONOT-83]
-	_ = x[OBITNOT-84]
-	_ = x[OPLUS-85]
-	_ = x[ONEG-86]
-	_ = x[OOROR-87]
-	_ = x[OPANIC-88]
-	_ = x[OPRINT-89]
-	_ = x[OPRINTN-90]
-	_ = x[OPAREN-91]
-	_ = x[OSEND-92]
-	_ = x[OSLICE-93]
-	_ = x[OSLICEARR-94]
-	_ = x[OSLICESTR-95]
-	_ = x[OSLICE3-96]
-	_ = x[OSLICE3ARR-97]
-	_ = x[OSLICEHEADER-98]
-	_ = x[ORECOVER-99]
-	_ = x[ORECV-100]
-	_ = x[ORUNESTR-101]
-	_ = x[OSELRECV2-102]
-	_ = x[OIOTA-103]
-	_ = x[OREAL-104]
-	_ = x[OIMAG-105]
-	_ = x[OCOMPLEX-106]
-	_ = x[OALIGNOF-107]
-	_ = x[OOFFSETOF-108]
-	_ = x[OSIZEOF-109]
-	_ = x[OMETHEXPR-110]
-	_ = x[OSTMTEXPR-111]
-	_ = x[OBLOCK-112]
-	_ = x[OBREAK-113]
-	_ = x[OCASE-114]
-	_ = x[OCONTINUE-115]
-	_ = x[ODEFER-116]
-	_ = x[OFALL-117]
-	_ = x[OFOR-118]
-	_ = x[OFORUNTIL-119]
-	_ = x[OGOTO-120]
-	_ = x[OIF-121]
-	_ = x[OLABEL-122]
-	_ = x[OGO-123]
-	_ = x[ORANGE-124]
-	_ = x[ORETURN-125]
-	_ = x[OSELECT-126]
-	_ = x[OSWITCH-127]
-	_ = x[OTYPESW-128]
-	_ = x[OFUNCINST-129]
-	_ = x[OTCHAN-130]
-	_ = x[OTMAP-131]
-	_ = x[OTSTRUCT-132]
-	_ = x[OTINTER-133]
-	_ = x[OTFUNC-134]
-	_ = x[OTARRAY-135]
-	_ = x[OTSLICE-136]
-	_ = x[OINLCALL-137]
-	_ = x[OEFACE-138]
-	_ = x[OITAB-139]
-	_ = x[OIDATA-140]
-	_ = x[OSPTR-141]
-	_ = x[OCFUNC-142]
-	_ = x[OCHECKNIL-143]
-	_ = x[OVARDEF-144]
-	_ = x[OVARKILL-145]
-	_ = x[OVARLIVE-146]
-	_ = x[ORESULT-147]
-	_ = x[OINLMARK-148]
-	_ = x[OLINKSYMOFFSET-149]
-	_ = x[OTAILCALL-150]
-	_ = x[OGETG-151]
-	_ = x[OEND-152]
+	_ = x[OSLICE2ARRPTR-21]
+	_ = x[OAS-22]
+	_ = x[OAS2-23]
+	_ = x[OAS2DOTTYPE-24]
+	_ = x[OAS2FUNC-25]
+	_ = x[OAS2MAPR-26]
+	_ = x[OAS2RECV-27]
+	_ = x[OASOP-28]
+	_ = x[OCALL-29]
+	_ = x[OCALLFUNC-30]
+	_ = x[OCALLMETH-31]
+	_ = x[OCALLINTER-32]
+	_ = x[OCALLPART-33]
+	_ = x[OCAP-34]
+	_ = x[OCLOSE-35]
+	_ = x[OCLOSURE-36]
+	_ = x[OCOMPLIT-37]
+	_ = x[OMAPLIT-38]
+	_ = x[OSTRUCTLIT-39]
+	_ = x[OARRAYLIT-40]
+	_ = x[OSLICELIT-41]
+	_ = x[OPTRLIT-42]
+	_ = x[OCONV-43]
+	_ = x[OCONVIFACE-44]
+	_ = x[OCONVNOP-45]
+	_ = x[OCOPY-46]
+	_ = x[ODCL-47]
+	_ = x[ODCLFUNC-48]
+	_ = x[ODCLCONST-49]
+	_ = x[ODCLTYPE-50]
+	_ = x[ODELETE-51]
+	_ = x[ODOT-52]
+	_ = x[ODOTPTR-53]
+	_ = x[ODOTMETH-54]
+	_ = x[ODOTINTER-55]
+	_ = x[OXDOT-56]
+	_ = x[ODOTTYPE-57]
+	_ = x[ODOTTYPE2-58]
+	_ = x[OEQ-59]
+	_ = x[ONE-60]
+	_ = x[OLT-61]
+	_ = x[OLE-62]
+	_ = x[OGE-63]
+	_ = x[OGT-64]
+	_ = x[ODEREF-65]
+	_ = x[OINDEX-66]
+	_ = x[OINDEXMAP-67]
+	_ = x[OKEY-68]
+	_ = x[OSTRUCTKEY-69]
+	_ = x[OLEN-70]
+	_ = x[OMAKE-71]
+	_ = x[OMAKECHAN-72]
+	_ = x[OMAKEMAP-73]
+	_ = x[OMAKESLICE-74]
+	_ = x[OMAKESLICECOPY-75]
+	_ = x[OMUL-76]
+	_ = x[ODIV-77]
+	_ = x[OMOD-78]
+	_ = x[OLSH-79]
+	_ = x[ORSH-80]
+	_ = x[OAND-81]
+	_ = x[OANDNOT-82]
+	_ = x[ONEW-83]
+	_ = x[ONOT-84]
+	_ = x[OBITNOT-85]
+	_ = x[OPLUS-86]
+	_ = x[ONEG-87]
+	_ = x[OOROR-88]
+	_ = x[OPANIC-89]
+	_ = x[OPRINT-90]
+	_ = x[OPRINTN-91]
+	_ = x[OPAREN-92]
+	_ = x[OSEND-93]
+	_ = x[OSLICE-94]
+	_ = x[OSLICEARR-95]
+	_ = x[OSLICESTR-96]
+	_ = x[OSLICE3-97]
+	_ = x[OSLICE3ARR-98]
+	_ = x[OSLICEHEADER-99]
+	_ = x[ORECOVER-100]
+	_ = x[ORECV-101]
+	_ = x[ORUNESTR-102]
+	_ = x[OSELRECV2-103]
+	_ = x[OIOTA-104]
+	_ = x[OREAL-105]
+	_ = x[OIMAG-106]
+	_ = x[OCOMPLEX-107]
+	_ = x[OALIGNOF-108]
+	_ = x[OOFFSETOF-109]
+	_ = x[OSIZEOF-110]
+	_ = x[OMETHEXPR-111]
+	_ = x[OSTMTEXPR-112]
+	_ = x[OBLOCK-113]
+	_ = x[OBREAK-114]
+	_ = x[OCASE-115]
+	_ = x[OCONTINUE-116]
+	_ = x[ODEFER-117]
+	_ = x[OFALL-118]
+	_ = x[OFOR-119]
+	_ = x[OFORUNTIL-120]
+	_ = x[OGOTO-121]
+	_ = x[OIF-122]
+	_ = x[OLABEL-123]
+	_ = x[OGO-124]
+	_ = x[ORANGE-125]
+	_ = x[ORETURN-126]
+	_ = x[OSELECT-127]
+	_ = x[OSWITCH-128]
+	_ = x[OTYPESW-129]
+	_ = x[OFUNCINST-130]
+	_ = x[OTCHAN-131]
+	_ = x[OTMAP-132]
+	_ = x[OTSTRUCT-133]
+	_ = x[OTINTER-134]
+	_ = x[OTFUNC-135]
+	_ = x[OTARRAY-136]
+	_ = x[OTSLICE-137]
+	_ = x[OINLCALL-138]
+	_ = x[OEFACE-139]
+	_ = x[OITAB-140]
+	_ = x[OIDATA-141]
+	_ = x[OSPTR-142]
+	_ = x[OCFUNC-143]
+	_ = x[OCHECKNIL-144]
+	_ = x[OVARDEF-145]
+	_ = x[OVARKILL-146]
+	_ = x[OVARLIVE-147]
+	_ = x[ORESULT-148]
+	_ = x[OINLMARK-149]
+	_ = x[OLINKSYMOFFSET-150]
+	_ = x[OTAILCALL-151]
+	_ = x[OGETG-152]
+	_ = x[OEND-153]
 }
 
-const _Op_name = "XXXNAMENONAMETYPEPACKLITERALNILADDSUBORXORADDSTRADDRANDANDAPPENDBYTES2STRBYTES2STRTMPRUNES2STRSTR2BYTESSTR2BYTESTMPSTR2RUNESASAS2AS2DOTTYPEAS2FUNCAS2MAPRAS2RECVASOPCALLCALLFUNCCALLMETHCALLINTERCALLPARTCAPCLOSECLOSURECOMPLITMAPLITSTRUCTLITARRAYLITSLICELITPTRLITCONVCONVIFACECONVNOPCOPYDCLDCLFUNCDCLCONSTDCLTYPEDELETEDOTDOTPTRDOTMETHDOTINTERXDOTDOTTYPEDOTTYPE2EQNELTLEGEGTDEREFINDEXINDEXMAPKEYSTRUCTKEYLENMAKEMAKECHANMAKEMAPMAKESLICEMAKESLICECOPYMULDIVMODLSHRSHANDANDNOTNEWNOTBITNOTPLUSNEGORORPANICPRINTPRINTNPARENSENDSLICESLICEARRSLICESTRSLICE3SLICE3ARRSLICEHEADERRECOVERRECVRUNESTRSELRECV2IOTAREALIMAGCOMPLEXALIGNOFOFFSETOFSIZEOFMETHEXPRSTMTEXPRBLOCKBREAKCASECONTINUEDEFERFALLFORFORUNTILGOTOIFLABELGORANGERETURNSELECTSWITCHTYPESWFUNCINSTTCHANTMAPTSTRUCTTINTERTFUNCTARRAYTSLICEINLCALLEFACEITABIDATASPTRCFUNCCHECKNILVARDEFVARKILLVARLIVERESULTINLMARKLINKSYMOFFSETTAILCALLGETGEND"
+const _Op_name = "XXXNAMENONAMETYPEPACKLITERALNILADDSUBORXORADDSTRADDRANDANDAPPENDBYTES2STRBYTES2STRTMPRUNES2STRSTR2BYTESSTR2BYTESTMPSTR2RUNESSLICE2ARRPTRASAS2AS2DOTTYPEAS2FUNCAS2MAPRAS2RECVASOPCALLCALLFUNCCALLMETHCALLINTERCALLPARTCAPCLOSECLOSURECOMPLITMAPLITSTRUCTLITARRAYLITSLICELITPTRLITCONVCONVIFACECONVNOPCOPYDCLDCLFUNCDCLCONSTDCLTYPEDELETEDOTDOTPTRDOTMETHDOTINTERXDOTDOTTYPEDOTTYPE2EQNELTLEGEGTDEREFINDEXINDEXMAPKEYSTRUCTKEYLENMAKEMAKECHANMAKEMAPMAKESLICEMAKESLICECOPYMULDIVMODLSHRSHANDANDNOTNEWNOTBITNOTPLUSNEGORORPANICPRINTPRINTNPARENSENDSLICESLICEARRSLICESTRSLICE3SLICE3ARRSLICEHEADERRECOVERRECVRUNESTRSELRECV2IOTAREALIMAGCOMPLEXALIGNOFOFFSETOFSIZEOFMETHEXPRSTMTEXPRBLOCKBREAKCASECONTINUEDEFERFALLFORFORUNTILGOTOIFLABELGORANGERETURNSELECTSWITCHTYPESWFUNCINSTTCHANTMAPTSTRUCTTINTERTFUNCTARRAYTSLICEINLCALLEFACEITABIDATASPTRCFUNCCHECKNILVARDEFVARKILLVARLIVERESULTINLMARKLINKSYMOFFSETTAILCALLGETGEND"
 
-var _Op_index = [...]uint16{0, 3, 7, 13, 17, 21, 28, 31, 34, 37, 39, 42, 48, 52, 58, 64, 73, 85, 94, 103, 115, 124, 126, 129, 139, 146, 153, 160, 164, 168, 176, 184, 193, 201, 204, 209, 216, 223, 229, 238, 246, 254, 260, 264, 273, 280, 284, 287, 294, 302, 309, 315, 318, 324, 331, 339, 343, 350, 358, 360, 362, 364, 366, 368, 370, 375, 380, 388, 391, 400, 403, 407, 415, 422, 431, 444, 447, 450, 453, 456, 459, 462, 468, 471, 474, 480, 484, 487, 491, 496, 501, 507, 512, 516, 521, 529, 537, 543, 552, 563, 570, 574, 581, 589, 593, 597, 601, 608, 615, 623, 629, 637, 645, 650, 655, 659, 667, 672, 676, 679, 687, 691, 693, 698, 700, 705, 711, 717, 723, 729, 737, 742, 746, 753, 759, 764, 770, 776, 783, 788, 792, 797, 801, 806, 814, 820, 827, 834, 840, 847, 860, 868, 872, 875}
+var _Op_index = [...]uint16{0, 3, 7, 13, 17, 21, 28, 31, 34, 37, 39, 42, 48, 52, 58, 64, 73, 85, 94, 103, 115, 124, 136, 138, 141, 151, 158, 165, 172, 176, 180, 188, 196, 205, 213, 216, 221, 228, 235, 241, 250, 258, 266, 272, 276, 285, 292, 296, 299, 306, 314, 321, 327, 330, 336, 343, 351, 355, 362, 370, 372, 374, 376, 378, 380, 382, 387, 392, 400, 403, 412, 415, 419, 427, 434, 443, 456, 459, 462, 465, 468, 471, 474, 480, 483, 486, 492, 496, 499, 503, 508, 513, 519, 524, 528, 533, 541, 549, 555, 564, 575, 582, 586, 593, 601, 605, 609, 613, 620, 627, 635, 641, 649, 657, 662, 667, 671, 679, 684, 688, 691, 699, 703, 705, 710, 712, 717, 723, 729, 735, 741, 749, 754, 758, 765, 771, 776, 782, 788, 795, 800, 804, 809, 813, 818, 826, 832, 839, 846, 852, 859, 872, 880, 884, 887}
 
 func (i Op) String() string {
 	if i >= Op(len(_Op_index)-1) {