Souper says:

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

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_380/foo.bc

LLVM says:

define void @fn2() #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %cmp = icmp eq i32 %0, 0
  %conv = zext i1 %cmp to i32
  %div.i = udiv i32 1, %conv
  store i32 %div.i, i32* @c, align 4, !tbaa !1
  %tobool.i = icmp eq i32 %div.i, 0
  br i1 %tobool.i, label %fn1.exit, label %if.then.i

if.then.i:                                        ; preds = %entry
  store i32 0, i32* @b, align 4, !tbaa !1
  br label %fn1.exit

fn1.exit:                                         ; preds = %entry, %if.then.i
  ret void
}
define void @fn1(i32 %p1) #0 {
entry:
  %div = sdiv i32 1, %p1
  store i32 %div, i32* @c, align 4, !tbaa !1
  %tobool = icmp eq i32 %div, 0
  br i1 %tobool, label %if.end, label %if.then

if.then:                                          ; preds = %entry
  store i32 0, i32* @b, align 4, !tbaa !1
  br label %if.end

if.end:                                           ; preds = %entry, %if.then
  ret void
}

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_380/foo.c -o reduce_380/foo.bc

C source code:

int a, b, c;
void fn1();
void fn2() { fn1(0 == a); }

void fn1(p1) {
  c = 1 / p1;
  if (c)
    b = 0;
}

x86-64 from LLVM:

fn2:                                    # @fn2
	cmpl	$0, a(%rip)
	sete	%al
	movzbl	%al, %ecx
	movl	$1, %eax
	xorl	%edx, %edx
	divl	%ecx
	testl	%eax, %eax
	movl	%eax, c(%rip)
	je	.LBB0_2
	movl	$0, b(%rip)
.LBB0_2:                                # %fn1.exit
	retq
fn1:                                    # @fn1
	movl	$1, %eax
	xorl	%edx, %edx
	idivl	%edi
	testl	%eax, %eax
	movl	%eax, c(%rip)
	je	.LBB1_2
	movl	$0, b(%rip)
.LBB1_2:                                # %if.end
	retq
.Ltmp1:

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_380/foo.c -S -o -

x86-64 from GCC:

fn2:
	movl	a(%rip), %eax
	xorl	%ecx, %ecx
	testl	%eax, %eax
	movl	$1, %eax
	sete	%cl
	cltd
	idivl	%ecx
	testl	%eax, %eax
	movl	%eax, c(%rip)
	je	.L1
	movl	$0, b(%rip)
.L1:
	rep ret
fn1:
.LFB1:
	movl	$1, %eax
	cltd
	idivl	%edi
	testl	%eax, %eax
	movl	%eax, c(%rip)
	je	.L7
	movl	$0, b(%rip)
.L7:
	rep ret
.LFE1:

COMMAND: gcc -w -O3 reduce_380/foo.c -S -o -