Souper says:

; Function: fn1
%0:i32 = var 
%1:i1 = eq 0:i32, %0
%2:i32 = zext %1
%3:i32 = or %0, %2
%4:i1 = eq 0:i32, %3
cand %4 0:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_783/foo.bc

LLVM says:

define void @fn1() #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %cmp = icmp eq i32 %0, 0
  %conv = zext i1 %cmp to i32
  store i32 %conv, i32* @b, align 4, !tbaa !1
  %or = or i32 %conv, %0
  %tobool = icmp eq i32 %or, 0
  br i1 %tobool, label %if.end, label %for.cond.preheader

for.cond.preheader:                               ; preds = %entry
  br label %for.cond

for.cond:                                         ; preds = %for.cond.preheader, %for.cond
  br label %for.cond

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

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_783/foo.c -o reduce_783/foo.bc

C source code:

int a, b;
void fn1() {
  b = a == 0;
  if (b | a)
    for (;;)
      ;
}

x86-64 from LLVM:

fn1:                                    # @fn1
	movl	a(%rip), %eax
	testl	%eax, %eax
	sete	%cl
	movzbl	%cl, %ecx
	movl	%ecx, b(%rip)
	orl	%eax, %ecx
	je	.LBB0_2
.LBB0_1:                                # %for.cond
	jmp	.LBB0_1
.LBB0_2:                                # %if.end
	retq

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_783/foo.c -S -o -

x86-64 from GCC:

fn1:
	movl	a(%rip), %eax
	xorl	%edx, %edx
	testl	%eax, %eax
	sete	%dl
	movl	%edx, b(%rip)
	orl	%eax, %edx
	je	.L1
.L3:
	jmp	.L3
.L1:
	rep ret

COMMAND: gcc -w -O3 reduce_783/foo.c -S -o -