Souper says:

; Function: fn2
%0:i32 = var 
%1:i32 = sdiv %0, 0:i32
%2:i1 = ne 0:i32, %1
cand %2 1:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_569/foo.bc

LLVM says:

define void @fn2() #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %div.i = sdiv i32 %0, 0
  %tobool.i = icmp ne i32 %div.i, 0
  %div..i = select i1 %tobool.i, i32 %div.i, i32 1
  store i32 %div..i, i32* @b, align 4, !tbaa !1
  ret void
}
define void @fn1(i32 %p1) #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %div = sdiv i32 %0, %p1
  %tobool = icmp ne i32 %div, 0
  %div. = select i1 %tobool, i32 %div, i32 1
  store i32 %div., i32* @b, align 4, !tbaa !1
  ret void
}

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_569/foo.c -o reduce_569/foo.bc

C source code:

int a, b;
void fn1();
void fn2() { fn1(); }

void fn1(p1) { b = a / p1 ?: 1; }

x86-64 from LLVM:

fn2:                                    # @fn2
	movl	a(%rip), %eax
	xorl	%ecx, %ecx
	cltd
	idivl	%ecx
	testl	%eax, %eax
	movl	$1, %ecx
	cmovnel	%eax, %ecx
	movl	%ecx, b(%rip)
	retq
fn1:                                    # @fn1
	movl	a(%rip), %eax
	cltd
	idivl	%edi
	testl	%eax, %eax
	movl	$1, %ecx
	cmovnel	%eax, %ecx
	movl	%ecx, b(%rip)
	retq
.Ltmp1:

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_569/foo.c -S -o -

x86-64 from GCC:

fn2:
	movl	a(%rip), %eax
	xorl	%ecx, %ecx
	cltd
	idivl	%ecx
	movb	$1, %cl
	testl	%eax, %eax
	cmovne	%eax, %ecx
	movl	%ecx, b(%rip)
	ret
fn1:
.LFB1:
	movl	a(%rip), %eax
	movl	$1, %ecx
	cltd
	idivl	%edi
	testl	%eax, %eax
	cmovne	%eax, %ecx
	movl	%ecx, b(%rip)
	ret
.LFE1:

COMMAND: gcc -w -O3 reduce_569/foo.c -S -o -