Souper says:

; Function: fn1
%0:i32 = var 
%1:i32 = var 
%2:i32 = and %0, %1
%3:i1 = slt %2, 0:i32
pc %3 1:i1
%4:i32 = subnsw 0:i32, %0
%5:i1 = slt %1, %4
cand %5 1:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_228/foo.bc

LLVM says:

define void @fn1() #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %1 = load i32* @b, align 4
  %2 = and i32 %1, %0
  %3 = icmp slt i32 %2, 0
  br i1 %3, label %land.rhs, label %land.end

land.rhs:                                         ; preds = %entry
  %sub = sub nsw i32 0, %1
  %cmp2 = icmp slt i32 %0, %sub
  br label %land.end

land.end:                                         ; preds = %land.rhs, %entry
  %4 = phi i1 [ false, %entry ], [ %cmp2, %land.rhs ]
  %land.ext = zext i1 %4 to i32
  store i32 %land.ext, i32* @c, align 4, !tbaa !1
  ret void
}

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_228/foo.c -o reduce_228/foo.bc

C source code:

int a, b, c;
void fn1() { c = a < 0 && b < 0 && a < -b; }

x86-64 from LLVM:

fn1:                                    # @fn1
	movl	a(%rip), %eax
	movl	b(%rip), %ecx
	testl	%eax, %ecx
	js	.LBB0_2
	xorl	%eax, %eax
	jmp	.LBB0_3
.LBB0_2:                                # %land.rhs
	negl	%ecx
	cmpl	%ecx, %eax
	setl	%al
.LBB0_3:                                # %land.end
	movzbl	%al, %eax
	movl	%eax, c(%rip)
	retq

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_228/foo.c -S -o -

x86-64 from GCC:

fn1:
	movl	a(%rip), %edx
	xorl	%eax, %eax
	testl	%edx, %edx
	js	.L5
	movl	%eax, c(%rip)
	ret
.L5:
	movl	b(%rip), %eax
	shrl	$31, %eax
	movl	%eax, c(%rip)
	ret

COMMAND: gcc -w -O3 reduce_228/foo.c -S -o -