Assembly code for iteration over StringPiece (by-value vs by-reference)

stringpieceitertest.s

# Source:
# void StringPieceIterTestVal(const std::vector<base::StringPiece>& vector) {
#   for (base::StringPiece piece : vector)
#     std::fwrite(piece.data(), piece.size(), 1, stdout);
# }
#
# void StringPieceIterTestRef(const std::vector<base::StringPiece>& vector) {
#   for (const base::StringPiece& piece : vector)
#     std::fwrite(piece.data(), piece.size(), 1, stdout);
# }
# (both functions generate same code)
#
# Compiler: clang++ Linux 64-bit

# BB#0:                                 # %entry
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register %rbp
	pushq	%r15
	pushq	%r14
	pushq	%rbx
	pushq	%rax
	.cfi_offset %rbx, -40
	.cfi_offset %r14, -32
	.cfi_offset %r15, -24
	movq	(%rdi), %rbx
	movq	8(%rdi), %r14
	cmpq	%r14, %rbx
	je	.LBB23_3
# BB#1:
	movq	stdout@GOTPCREL(%rip), %r15
	.p2align	4, 0x90
.LBB23_2:                               # %for.body
	movq	(%rbx), %rdi
	movq	8(%rbx), %rsi
	movq	(%r15), %rcx
	movl	$1, %edx
	callq	fwrite@PLT
	addq	$16, %rbx
	cmpq	%r14, %rbx
	jne	.LBB23_2
.LBB23_3:                               # %for.cond.cleanup
	addq	$8, %rsp
	popq	%rbx
	popq	%r14
	popq	%r15
	popq	%rbp
	retq