Souper says:

; Function: fn1
%0:i32 = var 
%1:i64 = sext %0
%2:i64 = and 9223372036854775807:i64, %1
%3:i1 = ne 0:i64, %2
%4:i32 = select %3, %0, 1:i32
%5:i1 = eq 0:i32, %4
cand %5 0:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_388/foo.bc

LLVM says:

define void @fn1() #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %conv = sext i32 %0 to i64
  %and = and i64 %conv, 9223372036854775807
  %tobool = icmp ne i64 %and, 0
  %conv1 = select i1 %tobool, i32 %0, i32 1
  store i32 %conv1, i32* @b, align 4, !tbaa !1
  %tobool2 = icmp eq i32 %conv1, 0
  br i1 %tobool2, 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_388/foo.c -o reduce_388/foo.bc

C source code:

int a, b;
void fn1() {
  b = a & 9223372036854775807 ?: 1;
  if (b)
    for (;;)
      ;
}

x86-64 from LLVM:

fn1:                                    # @fn1
	movslq	a(%rip), %rax
	movabsq	$9223372036854775807, %rcx # imm = 0x7FFFFFFFFFFFFFFF
	testq	%rcx, %rax
	movl	$1, %ecx
	cmovnel	%eax, %ecx
	testl	%ecx, %ecx
	movl	%ecx, b(%rip)
	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_388/foo.c -S -o -

x86-64 from GCC:

fn1:
	movslq	a(%rip), %rdx
	movabsq	$9223372036854775807, %rax
	andq	%rdx, %rax
	je	.L2
	testl	%eax, %eax
	movl	%eax, b(%rip)
	jne	.L5
	rep ret
.L2:
.L5:
.L4:
	jmp	.L4

COMMAND: gcc -w -O3 reduce_388/foo.c -S -o -