Souper says:

; Function: fn1
%0:i16 = var 
%1:i1 = slt %0, 1:i16
pc %1 1:i1
%2:i16 = add 1:i16, %0
%3:i1 = slt 1:i16, %2
cand %3 0:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_538/foo.bc

LLVM says:

define void @fn1() #0 {
entry:
  %.pr = load i16* @a, align 2, !tbaa !1
  %cmp2 = icmp slt i16 %.pr, 1
  br i1 %cmp2, label %for.body.lr.ph, label %for.end

for.body.lr.ph:                                   ; preds = %entry
  %0 = add i16 %.pr, 1
  %1 = icmp sgt i16 %0, 1
  %smax = select i1 %1, i16 %0, i16 1
  store i32 0, i32* @b, align 4, !tbaa !5
  store i16 %smax, i16* @a, align 2, !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_538/foo.c -o reduce_538/foo.bc

C source code:

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

x86-64 from LLVM:

fn1:                                    # @fn1
	movw	a(%rip), %ax
	testw	%ax, %ax
	jg	.LBB0_2
	incl	%eax
	testw	%ax, %ax
	movw	$1, %cx
	cmovgw	%ax, %cx
	movl	$0, b(%rip)
	movw	%cx, a(%rip)
.LBB0_2:                                # %for.end
	retq

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_538/foo.c -S -o -

x86-64 from GCC:

fn1:
	cmpw	$0, a(%rip)
	jg	.L1
	movl	$1, %eax
	movl	$0, b(%rip)
	movw	%ax, a(%rip)
.L1:
	rep ret

COMMAND: gcc -w -O3 reduce_538/foo.c -S -o -