Souper says:

; Function: fn3
%0:i32 = var 
%1:i1 = eq 0:i32, %0
pc %1 0:i1
%2:i32 = var 
%3:i1 = ne 0:i32, %2
%4:i32 = zext %3
%5:i32 = select %3, %4, %0
%6:i1 = eq 0:i32, %5
cand %6 0:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_123/foo.bc

LLVM says:

define i32 @fn1() #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %tobool = icmp eq i32 %0, 0
  br i1 %tobool, label %land.end, label %land.rhs

land.rhs:                                         ; preds = %entry
  %1 = load i32* @b, align 4, !tbaa !1
  %tobool1 = icmp ne i32 %1, 0
  br label %land.end

land.end:                                         ; preds = %entry, %land.rhs
  %2 = phi i1 [ false, %entry ], [ %tobool1, %land.rhs ]
  %land.ext = zext i1 %2 to i32
  %cond = select i1 %2, i32 %land.ext, i32 %0
  ret i32 %cond
}
define void @fn3() #1 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %tobool.i.i = icmp eq i32 %0, 0
  %1 = load i32* @b, align 4, !tbaa !1
  %tobool1.i.i = icmp ne i32 %1, 0
  br i1 %tobool.i.i, label %fn1.exit.us.i.preheader, label %fn1.exit.i.preheader

fn1.exit.us.i.preheader:                          ; preds = %entry
  br label %fn1.exit.us.i

fn1.exit.i.preheader:                             ; preds = %entry
  %land.ext.i.i = zext i1 %tobool1.i.i to i32
  %cond.i.i = select i1 %tobool1.i.i, i32 %land.ext.i.i, i32 %0
  %tobool.i = icmp eq i32 %cond.i.i, 0
  br i1 %tobool.i, label %fn1.exit.i.preheader2, label %for.cond1.i.preheader

for.cond1.i.preheader:                            ; preds = %fn1.exit.i.preheader
  br label %for.cond1.i

fn1.exit.i.preheader2:                            ; preds = %fn1.exit.i.preheader
  br label %fn1.exit.i

fn1.exit.us.i:                                    ; preds = %fn1.exit.us.i.preheader, %fn1.exit.us.i
  br label %fn1.exit.us.i

fn1.exit.i:                                       ; preds = %fn1.exit.i.preheader2, %fn1.exit.i
  br label %fn1.exit.i

for.cond1.i:                                      ; preds = %for.cond1.i.preheader, %for.cond1.i
  br label %for.cond1.i
}

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_123/foo.c -o reduce_123/foo.bc

C source code:

int a, b;
int fn1() { return a && b ?: a; }

static int fn2() {
  for (;;) {
    int c = fn1();
    if (c)
      for (;;)
        ;
  }
}

void fn3() { fn2(); }

x86-64 from LLVM:

fn1:                                    # @fn1
	movl	a(%rip), %eax
	testl	%eax, %eax
	je	.LBB0_1
	cmpl	$0, b(%rip)
	setne	%cl
	jmp	.LBB0_3
.LBB0_1:
	xorl	%ecx, %ecx
.LBB0_3:                                # %land.end
	movzbl	%cl, %ecx
	testb	%cl, %cl
	cmovnel	%ecx, %eax
	retq
fn3:                                    # @fn3
	movl	a(%rip), %eax
	testl	%eax, %eax
	je	.LBB1_4
	movl	b(%rip), %ecx
	testl	%ecx, %ecx
	setne	%cl
	movzbl	%cl, %ecx
	cmovnel	%ecx, %eax
	testl	%eax, %eax
	je	.LBB1_2
.LBB1_3:                                # %for.cond1.i
	jmp	.LBB1_3
.LBB1_4:                                # %fn1.exit.us.i
	jmp	.LBB1_4
.LBB1_2:                                # %fn1.exit.i
	jmp	.LBB1_2
.Ltmp1:

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_123/foo.c -S -o -

x86-64 from GCC:

fn1:
	movl	a(%rip), %edx
	xorl	%eax, %eax
	testl	%edx, %edx
	je	.L2
	movl	b(%rip), %ecx
	movb	$1, %al
	testl	%ecx, %ecx
	cmove	%edx, %eax
.L2:
	rep ret
fn3:
.LFB2:
	movl	a(%rip), %eax
	testl	%eax, %eax
	jne	.L8
.L9:
	jmp	.L9
.L8:
.L10:
	jmp	.L10
.LFE2:

COMMAND: gcc -w -O3 reduce_123/foo.c -S -o -