Souper says:

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

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_22/foo.bc

LLVM says:

define void @fn1() #0 {
entry:
  %0 = load i32* @b, align 4, !tbaa !1
  %cmp1 = icmp sgt i32 %0, 0
  %a.promoted = load i32* @a, align 4
  br i1 %cmp1, label %entry.split.us, label %entry.entry.split_crit_edge

entry.entry.split_crit_edge:                      ; preds = %entry
  %cmp2 = icmp slt i32 %a.promoted, %0
  %lor.ext = zext i1 %cmp2 to i32
  %lor.ext. = select i1 %cmp2, i32 %lor.ext, i32 0
  br label %for.end

entry.split.us:                                   ; preds = %entry
  %tobool.us = icmp ne i32 %a.promoted, 0
  %cmp2.us = icmp slt i32 %a.promoted, %0
  %.cmp2.us = or i1 %tobool.us, %cmp2.us
  %lor.ext.us = zext i1 %.cmp2.us to i32
  %lor.ext..us = select i1 %.cmp2.us, i32 %lor.ext.us, i32 0
  br label %for.end

for.end:                                          ; preds = %entry.split.us, %entry.entry.split_crit_edge
  %lor.ext..lcssa = phi i32 [ %lor.ext., %entry.entry.split_crit_edge ], [ %lor.ext..us, %entry.split.us ]
  store i32 %lor.ext..lcssa, i32* @a, align 4
  ret void
}

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_22/foo.c -o reduce_22/foo.bc

C source code:

int a, b;
void fn1() {
  int c = 0;
  for (; c >= 0; c--)
    a = b > 0 && a || a < b ?: 0;
}

x86-64 from LLVM:

fn1:                                    # @fn1
	movl	b(%rip), %eax
	testl	%eax, %eax
	movl	a(%rip), %ecx
	jle	.LBB0_1
	testl	%ecx, %ecx
	setne	%dl
	cmpl	%eax, %ecx
	setl	%al
	xorl	%ecx, %ecx
	orb	%dl, %al
	movzbl	%al, %eax
	cmovel	%ecx, %eax
	movl	%eax, a(%rip)
	retq
.LBB0_1:                                # %entry.entry.split_crit_edge
	xorl	%edx, %edx
	cmpl	%eax, %ecx
	setl	%al
	movzbl	%al, %eax
	cmovgel	%edx, %eax
	movl	%eax, a(%rip)
	retq

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_22/foo.c -S -o -

x86-64 from GCC:

fn1:
	movl	b(%rip), %eax
	movl	a(%rip), %edx
	testl	%eax, %eax
	jle	.L4
	movl	a(%rip), %edx
	testl	%edx, %edx
	je	.L5
	movl	$1, %eax
	movl	%eax, a(%rip)
	ret
.L5:
	xorl	%edx, %edx
.L4:
	cmpl	%eax, %edx
	setl	%al
	movzbl	%al, %eax
	movl	%eax, a(%rip)
	ret

COMMAND: gcc -w -O3 reduce_22/foo.c -S -o -