Souper says:

; Function: fn2
%0:i32 = var 
%1:i32 = ashr 4294955978:i32, %0
%2:i1 = slt %1, 1:i32
cand %2 1:i1

COMMAND: /home/regehr/souper/build/souper -stp-path=/usr/local/bin/stp reduce_744/foo.bc

LLVM says:

define void @fn2() #0 {
entry:
  %0 = load i32* @a, align 4, !tbaa !1
  %shr.i = ashr i32 -11318, %0
  %cmp.i = icmp slt i32 %shr.i, 1
  %conv2.i = zext i1 %cmp.i to i32
  store i32 %conv2.i, i32* @a, align 4, !tbaa !1
  ret void
}
define void @fn1(i64 %p1) #0 {
entry:
  %conv = trunc i64 %p1 to i32
  %sext = shl i32 %conv, 16
  %conv1 = ashr exact i32 %sext, 16
  %0 = load i32* @a, align 4, !tbaa !1
  %shr = ashr i32 %conv1, %0
  %cmp = icmp slt i32 %shr, 1
  %conv2 = zext i1 %cmp to i32
  store i32 %conv2, i32* @a, align 4, !tbaa !1
  ret void
}

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -c -w -emit-llvm -O3 reduce_744/foo.c -o reduce_744/foo.bc

C source code:

int a;
void fn1(unsigned long long);
void fn2() { fn1(54218); }

void fn1(unsigned long long p1) {
  short b = p1;
  a = b >> a < 1;
}

x86-64 from LLVM:

fn2:                                    # @fn2
	movb	a(%rip), %cl
	movl	$-11318, %eax           # imm = 0xFFFFFFFFFFFFD3CA
	sarl	%cl, %eax
	testl	%eax, %eax
	setle	%al
	movzbl	%al, %eax
	movl	%eax, a(%rip)
	retq
fn1:                                    # @fn1
	movswl	%di, %eax
	movb	a(%rip), %cl
	sarl	%cl, %eax
	testl	%eax, %eax
	setle	%al
	movzbl	%al, %eax
	movl	%eax, a(%rip)
	retq
.Ltmp1:

COMMAND: /home/regehr/souper/third_party/llvm/Debug/bin/clang -w -O3 reduce_744/foo.c -S -o -

x86-64 from GCC:

fn2:
	movl	a(%rip), %ecx
	movl	$-11318, %eax
	sarl	%cl, %eax
	testl	%eax, %eax
	setle	%al
	movzbl	%al, %eax
	movl	%eax, a(%rip)
	ret
fn1:
.LFB1:
	movl	a(%rip), %ecx
	movswl	%di, %edi
	xorl	%eax, %eax
	sarl	%cl, %edi
	testl	%edi, %edi
	setle	%al
	movl	%eax, a(%rip)
	ret
.LFE1:

COMMAND: gcc -w -O3 reduce_744/foo.c -S -o -