compiler: fix emission of large object layouts

Large object layouts don't fit in a pointer-sized integer and therefore
need to be stored in a global instead. However, the way the data was
stored in these globals was not correct for buffers that don't have
pointers near the end. This commit fixes this issue by using math/big
FillBytes() instead of Bytes().

This gets the unicode package to compile on AVR.

compiler/llvm.go

@@ -147,7 +147,7 @@ func (c *compilerContext) createObjectLayout(t llvm.Type, pos token.Pos) llvm.Va
 
 	// Create the global initializer.
 	bitmapBytes := make([]byte, int(objectSizeWords+7)/8)
-	copy(bitmapBytes, bitmap.Bytes())
+	bitmap.FillBytes(bitmapBytes)
 	var bitmapByteValues []llvm.Value
 	for _, b := range bitmapBytes {
 		bitmapByteValues = append(bitmapByteValues, llvm.ConstInt(c.ctx.Int8Type(), uint64(b), false))

compiler/testdata/gc.go

@@ -20,6 +20,10 @@ var (
 		y [60]uintptr
 		z *byte
 	}
+	struct4 *struct {
+		x *byte
+		y [61]uintptr
+	}
 
 	slice1 []byte
 	slice2 []*int
@@ -50,6 +54,10 @@ func newStruct() {
 		y [60]uintptr
 		z *byte
 	})
+	struct4 = new(struct {
+		x *byte
+		y [61]uintptr
+	})
 }
 
 func newFuncValue() *func() {

compiler/testdata/gc.ll

@@ -17,10 +17,12 @@ target triple = "wasm32-unknown-wasi"
 @main.struct1 = hidden global {}* null, align 4
 @main.struct2 = hidden global { i32, i32 }* null, align 4
 @main.struct3 = hidden global { i8*, [60 x i32], i8* }* null, align 4
+@main.struct4 = hidden global { i8*, [61 x i32] }* null, align 4
 @main.slice1 = hidden global { i8*, i32, i32 } zeroinitializer, align 8
 @main.slice2 = hidden global { i32**, i32, i32 } zeroinitializer, align 8
 @main.slice3 = hidden global { { i8*, i32, i32 }*, i32, i32 } zeroinitializer, align 8
 @"runtime/gc.layout:62-2000000000000001" = linkonce_odr unnamed_addr constant { i32, [8 x i8] } { i32 62, [8 x i8] c" \00\00\00\00\00\00\01" }
+@"runtime/gc.layout:62-0001" = linkonce_odr unnamed_addr constant { i32, [8 x i8] } { i32 62, [8 x i8] c"\00\00\00\00\00\00\00\01" }
 @"reflect/types.type:basic:complex128" = linkonce_odr constant %runtime.typecodeID { %runtime.typecodeID* null, i32 0, %runtime.interfaceMethodInfo* null, %runtime.typecodeID* @"reflect/types.type:pointer:basic:complex128", i32 0 }
 @"reflect/types.type:pointer:basic:complex128" = linkonce_odr constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:basic:complex128", i32 0, %runtime.interfaceMethodInfo* null, %runtime.typecodeID* null, i32 0 }
 
@@ -67,6 +69,8 @@ entry:
   store i8* %new1, i8** bitcast ({ i32, i32 }** @main.struct2 to i8**), align 4
   %new2 = call i8* @runtime.alloc(i32 248, i8* bitcast ({ i32, [8 x i8] }* @"runtime/gc.layout:62-2000000000000001" to i8*), i8* undef, i8* null) #0
   store i8* %new2, i8** bitcast ({ i8*, [60 x i32], i8* }** @main.struct3 to i8**), align 4
+  %new3 = call i8* @runtime.alloc(i32 248, i8* bitcast ({ i32, [8 x i8] }* @"runtime/gc.layout:62-0001" to i8*), i8* undef, i8* null) #0
+  store i8* %new3, i8** bitcast ({ i8*, [61 x i32] }** @main.struct4 to i8**), align 4
   ret void
 }