[LLVMdev] struct with signed bitfield (PR17827)

[Kay Tiong Khoo]

I've been diagnosing this bug:
http://llvm.org/bugs/show_bug.cgi?id=17827

Summary: I think the following program miscompiles at -O1 because the fact
that 'f0' is a signed 3-bit value is lost in the unoptimized LLVM IR. How
do we fix this?

$ cat bitfield.c
/* %struct.S = type { i8, [3 x i8] } ??? */
struct S {
  int f0:3;
} a;

int foo (int p) {
  struct S c = a;
  c.f0 = p & 6;
  return c.f0 < 1;
}

int main () {
  return foo (4);
}
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