Souper says:

; Function: fn2
%0:i32 = var 
%1:i1 = ne 0:i32, %0
%2:i32 = zext %1
%3:i32 = udiv 1:i32, %2
%4:i1 = ne 0:i32, %3
cand %4 1:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_789/foo.bc

LLVM says:

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

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_789/foo.c -o reduce_789/foo.bc

C source code:

int a, b;
int fn1(p1) { return 1 / p1 ?: 1; }

void fn2() {
  int c = fn1(a && 1);
  b = c;
}

x86-64 from LLVM:

fn1:                                    # @fn1
	movl	$1, %ecx
	movl	$1, %eax
	xorl	%edx, %edx
	idivl	%edi
	testl	%eax, %eax
	cmovnel	%eax, %ecx
	movl	%ecx, %eax
	retq
fn2:                                    # @fn2
	cmpl	$0, a(%rip)
	setne	%al
	movzbl	%al, %ecx
	movl	$1, %esi
	movl	$1, %eax
	xorl	%edx, %edx
	divl	%ecx
	testl	%eax, %eax
	cmovnel	%eax, %esi
	movl	%esi, b(%rip)
	retq
.Ltmp1:

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_789/foo.c -S -o -

x86-64 from GCC:

fn1:
	movl	$1, %ecx
	movl	%ecx, %eax
	cltd
	idivl	%edi
	testl	%eax, %eax
	cmove	%ecx, %eax
	ret
fn2:
.LFB1:
	movl	$1, b(%rip)
	ret
.LFE1:

COMMAND: gcc -w -O3 reduce_789/foo.c -S -o -