[LLVMbugs] [Bug 16710] New: Failure to constant-fold vector global

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16710

            Bug ID: 16710
           Summary: Failure to constant-fold vector global
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Interprocedural Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: silvas at purdue.edu
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

We are not able to constant-fold the use of `Global.Member` in this code (with
clang -O3):

typedef float __m128 __attribute__((__vector_size__(16)));
class GlobalType {
public:
  GlobalType(float F) {
    Member = (__m128){F, F, F, F}; // simplified from _mm_load1_ps
  }
  __m128 Member;
};
static const GlobalType Global = 42.0f;

__m128 use(__m128 V) {
  return V * Global.Member;
}

However, we *are* able to fold this:

class GlobalType {
public:
  GlobalType(float F) {
    Member = F;
  }
  float Member;
};
static const GlobalType Global = 42.0f;

float use(float V) {
  return V * Global.Member;
}

In the float case, the folding happens in -globalopt.

(Note: running an extra `-globalopt -constprop` after the standard -O3
optimizations does fold it; for some reason -globalopt only folds the value of
the global, but doesn't substitute its use).

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