Souper says:

; Function: fn1
%0:i32 = var 
%1:i1 = slt %0, 0:i32
pc %1 1:i1
%2:i32 = add 1:i32, %0
%3:i1 = slt 0:i32, %2
cand %3 0:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_756/foo.bc

LLVM says:

define void @fn1() #0 {
entry:
  %.pr = load i32* @b, align 4, !tbaa !1
  %cmp1 = icmp slt i32 %.pr, 0
  br i1 %cmp1, label %for.body.lr.ph, label %for.end

for.body.lr.ph:                                   ; preds = %entry
  %0 = add i32 %.pr, 1
  %1 = icmp sgt i32 %0, 0
  %smax = select i1 %1, i32 %0, i32 0
  store i32 0, i32* @a, align 4, !tbaa !1
  store i32 %smax, i32* @b, align 4, !tbaa !1
  br label %for.end

for.end:                                          ; preds = %for.body.lr.ph, %entry
  ret void
}

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_756/foo.c -o reduce_756/foo.bc

C source code:

int a, b;
void fn1() {
  for (; b < 0; b++)
    a = 0;
}

x86-64 from LLVM:

fn1:                                    # @fn1
	movl	b(%rip), %eax
	testl	%eax, %eax
	jns	.LBB0_2
	xorl	%ecx, %ecx
	incl	%eax
	cmovsl	%ecx, %eax
	movl	$0, a(%rip)
	movl	%eax, b(%rip)
.LBB0_2:                                # %for.end
	retq

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_756/foo.c -S -o -

x86-64 from GCC:

fn1:
	movl	b(%rip), %eax
	testl	%eax, %eax
	jns	.L1
	movl	$0, a(%rip)
	movl	$0, b(%rip)
.L1:
	rep ret

COMMAND: gcc -w -O3 reduce_756/foo.c -S -o -