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

3 files changed, 37 insertions, 26 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{
diff --git a/pkg/csource/csource.go b/pkg/csource/csource.go
index 24717a31a..c30db6b9d 100644
--- a/pkg/csource/csource.go
+++ b/pkg/csource/csource.go
@@ -366,8 +366,13 @@ func (ctx *context) copyin(w *bytes.Buffer, csumSeq *int, copyin prog.ExecCopyin
 	case prog.ExecArgResult:
 		ctx.copyinVal(w, copyin.Addr, arg.Size, ctx.resultArgToStr(arg), arg.Format)
 	case prog.ExecArgData:
-		fmt.Fprintf(w, "\tNONFAILING(memcpy((void*)0x%x, \"%s\", %v));\n",
-			copyin.Addr, toCString(arg.Data, arg.Readable), len(arg.Data))
+		if bytes.Equal(arg.Data, bytes.Repeat(arg.Data[:1], len(arg.Data))) {
+			fmt.Fprintf(w, "\tNONFAILING(memset((void*)0x%x, %v, %v));\n",
+				copyin.Addr, arg.Data[0], len(arg.Data))
+		} else {
+			fmt.Fprintf(w, "\tNONFAILING(memcpy((void*)0x%x, \"%s\", %v));\n",
+				copyin.Addr, toCString(arg.Data, arg.Readable), len(arg.Data))
+		}
 	case prog.ExecArgCsum:
 		switch arg.Kind {
 		case prog.ExecArgCsumInet:
diff --git a/pkg/csource/csource_test.go b/pkg/csource/csource_test.go
index 752ff919b..e2035b286 100644
--- a/pkg/csource/csource_test.go
+++ b/pkg/csource/csource_test.go
@@ -160,37 +160,19 @@ csource2(&AUTO="12345678")
 csource3(&AUTO)
 csource4(&AUTO)
 csource5(&AUTO)
+csource6(&AUTO)
 `,
 			output: `
 NONFAILING(memcpy((void*)0x20000040, "\x12\x34\x56\x78", 4));
 syscall(SYS_csource2, 0x20000040ul);
-NONFAILING(*(uint8*)0x20000080 = 0);
-NONFAILING(*(uint8*)0x20000081 = 0);
-NONFAILING(*(uint8*)0x20000082 = 0);
-NONFAILING(*(uint8*)0x20000083 = 0);
-NONFAILING(*(uint8*)0x20000084 = 0);
-NONFAILING(*(uint8*)0x20000085 = 0);
-NONFAILING(*(uint8*)0x20000086 = 0);
-NONFAILING(*(uint8*)0x20000087 = 0);
-NONFAILING(*(uint8*)0x20000088 = 0);
-NONFAILING(*(uint8*)0x20000089 = 0);
+NONFAILING(memset((void*)0x20000080, 0, 10));
 syscall(SYS_csource3, 0x20000080ul);
-NONFAILING(*(uint8*)0x200000c0 = 0xab);
-NONFAILING(*(uint8*)0x200000c1 = 0xab);
-NONFAILING(*(uint8*)0x200000c2 = 0xab);
-NONFAILING(*(uint8*)0x200000c3 = 0xab);
-NONFAILING(*(uint8*)0x200000c4 = 0xab);
-NONFAILING(*(uint8*)0x200000c5 = 0xab);
-NONFAILING(*(uint8*)0x200000c6 = 0xab);
-NONFAILING(*(uint8*)0x200000c7 = 0xab);
-NONFAILING(*(uint8*)0x200000c8 = 0xab);
-NONFAILING(*(uint8*)0x200000c9 = 0xab);
+NONFAILING(memset((void*)0x200000c0, 48, 10));
 syscall(SYS_csource4, 0x200000c0ul);
-NONFAILING(*(uint32*)0x20000100 = 0x12345678);
-NONFAILING(*(uint32*)0x20000104 = 0x12345678);
-NONFAILING(*(uint32*)0x20000108 = 0x12345678);
-NONFAILING(*(uint32*)0x2000010c = 0x12345678);
+NONFAILING(memcpy((void*)0x20000100, "0101010101", 10));
 syscall(SYS_csource5, 0x20000100ul);
+NONFAILING(memcpy((void*)0x20000140, "101010101010", 12));
+syscall(SYS_csource6, 0x20000140ul);
 `,
 		},
 	}