[llvm-bugs] [Bug 41121] New: After r348496, "Unable to predicate BX killed renamable $r0"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41121

            Bug ID: 41121
           Summary: After r348496, "Unable to predicate BX killed
                    renamable $r0"
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: dimitry at andric.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

As described in https://bugs.freebsd.org/236567, compiling the FreeBSD
lang/spidermonkey170 or lang/spidermonkey38 ports for armv7 or armv6 errors out
with (note the strange error formatting, this is verbatim):

Unable to predicate BX killed renamable $r0
!
UNREACHABLE executed at lib/CodeGen/IfConversion.cpp:2022!

Bisection shows this started occurring after https://reviews.llvm.org/rL348496
("[GVN] Don't perform scalar PRE on GEPs").

Minimized test case:

// clang -cc1 -triple armv7-- -S -O2 Unified_cpp_js_src10-min.cpp
template <typename> struct c;
template <typename b> struct j : c<b> {
  j(int);
  b *aa() { return d; }
  b e() { return *d; }
  b *d;
};
typedef struct {
  struct {
    union {
      int f;
      int *ab;
    } g;
  } h;
} i;
struct n {
  int *k() { return ac.h.g.ab; }
  int l() { return ac.h.g.f; }
  i ac;
};
template <class m> struct p {
  int ad();
  int *k() {
    n o = *static_cast<m *>(this)->ae();
    return o.k();
  }
};
template <> struct c<n> : p<j<n>> {
  n *ae() { return static_cast<j<n> *>(this)->aa(); }
};
void fn1(bool *);
bool q;
int r;
void u() {
  void *a[]{&&s, &&t};
t:
  fn1(&q);
  goto *a[r];
s:;
}
int v(j<n> w, j<n> x, bool *y) {
  if (w.ad()) {
    *y = w.k() == x.k();
    return 0;
  }
  *y = w.e().l() == x.e().l();
  return 0;
}
void fn1(bool *w) { v(0, 0, w); }

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