int SPI_PUMP() {
  int r = 0;
  *(volatile unsigned int *)(0xFFFFFFD0 + 0x04) = (0xFF);
  r = (*(volatile unsigned int *)(0xFFFFFFD0 + 0x04) & 255);
  *(volatile unsigned int *)(0xFFFFFFD0 + 0x04) = (0xFF);
  r = (r << 8) | (*(volatile unsigned int *)(0xFFFFFFD0 + 0x04) & 255);
  *(volatile unsigned int *)(0xFFFFFFD0 + 0x04) = (0xFF);
  r = (r << 8) | (*(volatile unsigned int *)(0xFFFFFFD0 + 0x04) & 255);
  *(volatile unsigned int *)(0xFFFFFFD0 + 0x04) = (0xFF);
  r = (r << 8) | (*(volatile unsigned int *)(0xFFFFFFD0 + 0x04) & 255);
  return (r);
}


x86 assembly (clang, -O0):
<SPI_PUMP>:
push   %rbp
mov    %rsp,%rbp
movl   $0x0,-0x4(%rbp)
mov    $0xffffffd4,%eax
movl   $0xff,(%rax)
mov    $0xffffffd4,%eax
mov    (%rax),%eax
and    $0xff,%eax
mov    %eax,-0x4(%rbp)
mov    $0xffffffd4,%eax
movl   $0xff,(%rax)
mov    -0x4(%rbp),%eax
shl    $0x8,%eax
mov    $0xffffffd4,%ecx
mov    (%rcx),%ecx
and    $0xff,%ecx
or     %ecx,%eax
mov    %eax,-0x4(%rbp)
mov    $0xffffffd4,%eax
movl   $0xff,(%rax)
mov    -0x4(%rbp),%eax
shl    $0x8,%eax
mov    $0xffffffd4,%ecx
mov    (%rcx),%ecx
and    $0xff,%ecx
or     %ecx,%eax
mov    %eax,-0x4(%rbp)
mov    $0xffffffd4,%eax
movl   $0xff,(%rax)
mov    -0x4(%rbp),%eax
shl    $0x8,%eax
mov    $0xffffffd4,%ecx
mov    (%rcx),%ecx
and    $0xff,%ecx
or     %ecx,%eax
mov    %eax,-0x4(%rbp)
mov    -0x4(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<SPI_PUMP>:
mov    $0xffffffd4,%eax
movl   $0xff,(%rax)
mov    (%rax),%ecx
movl   $0xff,(%rax)
mov    (%rax),%edx
movl   $0xff,(%rax)
mov    (%rax),%esi
movl   $0xff,(%rax)
shl    $0x18,%ecx
movzbl %dl,%edx
shl    $0x10,%edx
or     %ecx,%edx
shl    $0x8,%esi
movzwl %si,%ecx
or     %edx,%ecx
mov    (%rax),%eax
movzbl %al,%eax
or     %ecx,%eax
ret

LLVM IR (-O0):
define i32 @SPI_PUMP() {
%1 = alloca i32
store i32 0, i32* %1
store volatile i32 255, i32* inttoptr (i64 4294967252 to i32*)
%2 = load volatile i32, i32* inttoptr (i64 4294967252 to i32*)
%3 = and i32 %2, 255
store i32 %3, i32* %1
store volatile i32 255, i32* inttoptr (i64 4294967252 to i32*)
%4 = load i32, i32* %1
%5 = shl i32 %4, 8
%6 = load volatile i32, i32* inttoptr (i64 4294967252 to i32*)
%7 = and i32 %6, 255
%8 = or i32 %5, %7
store i32 %8, i32* %1
store volatile i32 255, i32* inttoptr (i64 4294967252 to i32*)
%9 = load i32, i32* %1
%10 = shl i32 %9, 8
%11 = load volatile i32, i32* inttoptr (i64 4294967252 to i32*)
%12 = and i32 %11, 255
%13 = or i32 %10, %12
store i32 %13, i32* %1
store volatile i32 255, i32* inttoptr (i64 4294967252 to i32*)
%14 = load i32, i32* %1
%15 = shl i32 %14, 8
%16 = load volatile i32, i32* inttoptr (i64 4294967252 to i32*)
%17 = and i32 %16, 255
%18 = or i32 %15, %17
store i32 %18, i32* %1
%19 = load i32, i32* %1
ret i32 %19
}

LLVM IR (-O2):
define i32 @SPI_PUMP() {
store volatile i32 255, i32* inttoptr (i64 4294967252 to i32*)
%1 = load volatile i32, i32* inttoptr (i64 4294967252 to i32*)
store volatile i32 255, i32* inttoptr (i64 4294967252 to i32*)
%2 = load volatile i32, i32* inttoptr (i64 4294967252 to i32*)
store volatile i32 255, i32* inttoptr (i64 4294967252 to i32*)
%3 = load volatile i32, i32* inttoptr (i64 4294967252 to i32*)
store volatile i32 255, i32* inttoptr (i64 4294967252 to i32*)
%4 = shl i32 %1, 24
%5 = shl i32 %2, 16
%6 = and i32 %5, 16711680
%7 = or i32 %6, %4
%8 = shl i32 %3, 8
%9 = and i32 %8, 65280
%10 = or i32 %9, %7
%11 = load volatile i32, i32* inttoptr (i64 4294967252 to i32*)
%12 = and i32 %11, 255
%13 = or i32 %10, %12
ret i32 %13
}