gistfile1.txt

julia> f4(x::Int) = (x <= 1000 && x > 0) ? Base.checked_add(Base.checked_sub(x,1),1) : 0
f4 (generic function with 1 method)

julia> code_llvm(f4,(Int,))

define i64 @julia_f418717(i64) {
top:
  %.off = add i64 %0, -1, !dbg !1590
  %1 = icmp ugt i64 %.off, 999, !dbg !1590
  br i1 %1, label %L5, label %if2, !dbg !1590

if2:                                              ; preds = %top
  %2 = call { i64, i1 } @llvm.ssub.with.overflow.i64(i64 %0, i64 1), !dbg !1590
  %3 = extractvalue { i64, i1 } %2, 1, !dbg !1590
  br i1 %3, label %fail, label %pass, !dbg !1590

fail:                                             ; preds = %if2
  %4 = load %jl_value_t** @jl_overflow_exception, align 8, !dbg !1590
  call void @jl_throw_with_superfluous_argument(%jl_value_t* %4, i32 1), !dbg !1590
  unreachable, !dbg !1590

pass:                                             ; preds = %if2
  %5 = extractvalue { i64, i1 } %2, 0, !dbg !1590
  %6 = call { i64, i1 } @llvm.sadd.with.overflow.i64(i64 %5, i64 1), !dbg !1590
  %7 = extractvalue { i64, i1 } %6, 1, !dbg !1590
  br i1 %7, label %fail3, label %pass4, !dbg !1590

fail3:                                            ; preds = %pass
  %8 = load %jl_value_t** @jl_overflow_exception, align 8, !dbg !1590
  call void @jl_throw_with_superfluous_argument(%jl_value_t* %8, i32 1), !dbg !1590
  unreachable, !dbg !1590

pass4:                                            ; preds = %pass
  %9 = extractvalue { i64, i1 } %6, 0, !dbg !1590
  ret i64 %9, !dbg !1590

L5:                                               ; preds = %top
  ret i64 0, !dbg !1590
}

julia> code_native(f4,(Int,))
	.text
Filename: none
Source line: 1
	push	RBP
	mov	RBP, RSP
Source line: 1
	lea	RCX, QWORD PTR [RDI - 1]
	cmp	RCX, 999
	jbe	4
	xor	EAX, EAX
	pop	RBP
	ret
	cmp	RDI, 1
	jo	16
	lea	RAX, QWORD PTR [RCX + 1]
	add	RCX, 1
	jo	2
	pop	RBP
	ret
	movabs	RAX, 139953980758368
	mov	RDI, QWORD PTR [RAX]
	movabs	RAX, 139953965933040
	mov	ESI, 1
	call	RAX

julia> f5(x::Int) = (x <= 1000 && x > 0) ? x : 0
f5 (generic function with 1 method)

julia> code_llvm(f5,(Int,))

define i64 @julia_f518718(i64) {
top:
  %.off = add i64 %0, -1, !dbg !1593
  %1 = icmp ugt i64 %.off, 999, !dbg !1593
  %merge = select i1 %1, i64 0, i64 %0, !dbg !1593
  ret i64 %merge, !dbg !1593
}

julia> code_native(f5,(Int,))
	.text
Filename: none
Source line: 1
	push	RBP
	mov	RBP, RSP
Source line: 1
	lea	RCX, QWORD PTR [RDI - 1]
	xor	EAX, EAX
	cmp	RCX, 999
	cmovbe	RAX, RDI
	pop	RBP
	ret

julia> versioninfo()
Julia Version 0.3.0-prerelease+3456
Commit dc53d93 (2014-06-03 22:37 UTC)
Platform Info:
  System: Linux (x86_64-unknown-linux-gnu)
  CPU: Intel(R) Core(TM) i7-3540M CPU @ 3.00GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY)
  LAPACK: libopenblas
  LIBM: libopenlibm

This is an example of the code that would be generated for a statement like length(1:n). If n is positive and less than the maximum value for integers, then this should just return n. However, the checks for overflow are not optimised away and remain as dead code paths.