[LLVMbugs] [Bug 13542] New: Problem with LICM optimization

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon Aug 6 23:30:34 PDT 2012


             Bug #: 13542
           Summary: Problem with LICM optimization
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: release blocker
          Priority: P
         Component: LLVM Codegen
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: rahul.s1 at samsung.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

For the below code after doing " O2 "  lever optimization , the code aborts as
per the test case.

extern "C" void * malloc(__SIZE_TYPE__);
extern "C" void abort(void);

void *p;
void __attribute__((noinline)) init(void)
  p = malloc(4);

inline void *operator new(__SIZE_TYPE__)
  return p;

inline void operator delete (void*) {}

int * __attribute__((noinline)) doit(int n)
  float *q;
  int *r;

  for (int i=0; i<n; ++i)
    q = new float;
    *q = 1.0;
    delete q;
    r = new int;
    *r = 1;

  return r;

int main()
  if (*doit(1) != 1)
  return 0;

For the doit function,
In the code flow , it seems that while doing LICM optimization , the store
instruction for float while getting promoted actually gets promoted below the
store for int . So in further alias analysis , the int operation is removed
which is setting the value to float store operation.

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