pkg/compiler: optimize array[const] representation

Represent array[const[X, int8], N] as string["XX...X"].

This replaces potentially huge number of:
		NONFAILING(*(uint8_t*)0x2000126c = 0);
		NONFAILING(*(uint8_t*)0x2000126d = 0);
		NONFAILING(*(uint8_t*)0x2000126e = 0);
with a single memcpy. In one reproducer we had 3991 such lines.

Also replace memcpy's with memset's when possible.

Update #1070

1 files changed, 24 insertions, 0 deletions

diff --git a/pkg/compiler/types.go b/pkg/compiler/types.go
index b2c8c3204..038a05f24 100644
--- a/pkg/compiler/types.go
+++ b/pkg/compiler/types.go
@@ -4,6 +4,8 @@
 package compiler
 
 import (
+	"bytes"
+	"encoding/binary"
 	"fmt"
 	"sort"
 	"strconv"
@@ -249,6 +251,28 @@ var typeArray = &typeDesc{
 				RangeEnd:   end,
 			}
 		}
+		if ct, ok := elemType.(*prog.ConstType); ok &&
+			(ct.ArgFormat == prog.FormatNative || ct.ArgFormat == prog.FormatBigEndian) &&
+			kind == prog.ArrayRangeLen && begin == end {
+			// Special case: const string takes less space in C programs.
+			base.TypeSize = begin * ct.Size()
+			base.TypeAlign = ct.TypeAlign
+			val := make([]byte, 8)
+			if ct.ArgFormat == prog.FormatBigEndian {
+				binary.BigEndian.PutUint64(val, ct.Val)
+				val = val[8-ct.Size():]
+			} else {
+				binary.LittleEndian.PutUint64(val, ct.Val)
+				val = val[:ct.Size()]
+			}
+			val = bytes.Repeat(val, int(begin))
+			return &prog.BufferType{
+				TypeCommon: base.TypeCommon,
+				Kind:       prog.BufferString,
+				Values:     []string{string(val)},
+				NoZ:        true,
+			}
+		}
 		// TypeSize is assigned later in layoutArray.
 		base.TypeAlign = elemType.Alignment()
 		return &prog.ArrayType{