Souper says:

; Function: fn1
%0:i32 = var 
%1:i64 = sext %0
%2:i64 = subnsw 2036854775807:i64, %1
%3:i1 = slt %2, 1:i64
cand %3 0:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_743/foo.bc

LLVM says:

define void @fn1() #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %conv = sext i32 %0 to i64
  %sub = sub nsw i64 2036854775807, %conv
  %cmp = icmp slt i64 %sub, 1
  %conv1 = zext i1 %cmp to i32
  store i32 %conv1, i32* @b, align 4, !tbaa !1
  ret void
}

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_743/foo.c -o reduce_743/foo.bc

C source code:

int a, b;
void fn1() { b = 2036854775807 - a < 1; }

x86-64 from LLVM:

fn1:                                    # @fn1
	movslq	a(%rip), %rax
	movabsq	$2036854775807, %rcx    # imm = 0x1DA3E015FFF
	subq	%rax, %rcx
	testq	%rcx, %rcx
	setle	%al
	movzbl	%al, %eax
	movl	%eax, b(%rip)
	retq

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_743/foo.c -S -o -

x86-64 from GCC:

fn1:
	movl	$0, b(%rip)
	ret

COMMAND: gcc -w -O3 reduce_743/foo.c -S -o -