Fix bad assert in print-changed code

[jamieschmeiser]

Summary

The assertion that both functions were not missing was incorrect and would
fail when one of the functions was missing. Fixed it and moved the
assertion earlier to check the input parameters to better capture
first-failure.

[aeubanks]

do you have a test case that triggers this?

[jamieschmeiser]

I'll come up with a lit test and attach it

[jamieschmeiser]

Add a lit test that triggered the assertion.

[aeubanks]

lgtm

[jamieschmeiser]

[NFC] Rename test to match PR name and move into directory so that it will only
be run on systems that have an appropriate diff.

[jamieschmeiser]

[NFC] remove blank lines at EOF

llvm/lib/Passes/StandardInstrumentations.cpp

if (!getModuleForComparison(IR)) {
     handleFunctionCompare(Name, Prefix, PassID, false,
                           Before.getData().begin()->getValue(),
                           After.getData().begin()->getValue());
     return;
   }
 
   ChangedIRData::report(
       Before, After, [&](const ChangedFuncData *B, const ChangedFuncData *A) {
+        assert((B || A) && "Both functions cannot be missing.");
         ChangedFuncData Missing;
         if (!B)
           B = &Missing;
         else if (!A)
           A = &Missing;
-        assert(B != &Missing && A != &Missing &&
-               "Both functions cannot be missing.");
         handleFunctionCompare(Name, Prefix, PassID, true, *B, *A);
       });
 }
 
 void ChangedIRComparer::analyzeIR(Any IR, ChangedIRData &Data) {
   if (const Module *M = getModuleForComparison(IR)) {
     // Create data for each existing/interesting function in the module.
     for (const Function &F : *M)