internal/load: use alias slice for determinism

Previously aliases were stored in a map which was causing
non-deterministic code generation (see recent build failures). This diff
changes to a slice to avoid this problem.

Updates mmcloughlin#50

internal/load/annoyingaliases.sh

@@ -12,7 +12,7 @@ arch=${GOROOT}/src/cmd/asm/internal/arch/arch.go
     echo
     echo 'package load'
     echo
-    echo 'var annoyingaliases = map[string]string{'
+    echo 'var annoyingaliases = []alias{'
 
     awk '
         /archX86/ { x86=1 }
@@ -27,7 +27,7 @@ arch=${GOROOT}/src/cmd/asm/internal/arch/arch.go
             sub(/x86\.A/, "", to)
 
             if(from != to) { 
-                printf("\t\"%s\": \"%s\",\n", from, to)
+                printf("\t{\"%s\", \"%s\"},\n", from, to)
             }
         }
     ' ${arch}

internal/load/load.go

@@ -74,15 +74,19 @@ func (l *Loader) Load() ([]inst.Instruction, error) {
 		im[e.Opcode] = e
 	}
 
-	// Apply list of aliases.
-	for from, to := range aliases {
-		if existing, found := im[from]; found {
-			im[to].Forms = append(im[to].Forms, existing.Forms...)
+	// Merge aliased forms. This is primarily for MOVQ (issue #50).
+	for _, a := range aliases {
+		if existing, found := im[a.From]; found {
+			im[a.To].Forms = append(im[a.To].Forms, existing.Forms...)
 		}
-		cpy := *im[to]
-		cpy.Opcode = from
-		cpy.AliasOf = to
-		im[from] = &cpy
+	}
+
+	// Apply list of aliases.
+	for _, a := range aliases {
+		cpy := *im[a.To]
+		cpy.Opcode = a.From
+		cpy.AliasOf = a.To
+		im[a.From] = &cpy
 	}
 
 	// Dedupe forms.

internal/load/tables.go

@@ -4,9 +4,15 @@ import (
 	"github.com/mmcloughlin/avo/internal/inst"
 )
 
+// alias defines an opcode alias.
+type alias struct {
+	From string
+	To   string
+}
+
 // aliases defines a list of opcode aliases. Where possible these are extracted
 // from the code (see note below).
-var aliases = map[string]string{
+var aliases = []alias{
 	// The PSHUFD/PSHUFL alias is not recorded in the list of "Annoying aliases" below. However the instructions are identical.
 	//
 	// Reference: https://github.com/golang/go/blob/048c9164a0c5572df18325e377473e7893dbfb07/src/cmd/internal/obj/x86/asm6.go#L1365
@@ -17,7 +23,7 @@ var aliases = map[string]string{
 	//
 	//		{APSHUFD, yxshuf, Pq, opBytes{0x70, 0}},
 	//
-	"PSHUFD": "PSHUFL",
+	{"PSHUFD", "PSHUFL"},
 }
 
 // Go contains a list of self-proclaimed "Annoying aliases", as follows. We use
@@ -88,9 +94,7 @@ var aliases = map[string]string{
 //go:generate ./annoyingaliases.sh zannoyingaliases.go
 
 func init() {
-	for from, to := range annoyingaliases {
-		aliases[from] = to
-	}
+	aliases = append(aliases, annoyingaliases...)
 }
 
 // extras is simply a list of extra instructions to add to the database.