[FastISel] fix a fallback diagnostic.

[igorb]

Summary

FastISel was marked as failed in case instruction selection succeeded.

[igorb]

ping

[zvi]

Is there a way to produce a test to cover this fix?

[ab]

There's a test for the call side in r294970, and I added some tests in r299093, you can probably make either check the generic fastisel fallback diagnostic too?

But in general, it's probably time to replace the function-level fallback diagnostic with the remarks, now that we have both.

@bogner, @qcolombet: do you guys still use the function diagnostic?

[igorb]

• add tests. Thanks.

[zvi]

LGTM

lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

if (FastIS) {
         }
 
         // Bottom-up: reset the insert pos at the top, after any local-value
         // instructions.
         FastIS->recomputeInsertPt();
 
         // Try to select the instruction with FastISel.
         if (FastIS->selectInstruction(Inst)) {
-          FastISelFailed = true;
           --NumFastIselRemaining;
           ++NumFastIselSuccess;
           // If fast isel succeeded, skip over all the folded instructions, and
           // then see if there is a load right before the selected instructions.
           // Try to fold the load if so.
           const Instruction *BeforeInst = Inst;
           while (BeforeInst != &*Begin) {
             BeforeInst = &*std::prev(BasicBlock::const_iterator(BeforeInst));
             if (!isFoldedOrDeadInstruction(BeforeInst, FuncInfo))
               break;
           }
           if (BeforeInst != Inst && isa<LoadInst>(BeforeInst) &&
               BeforeInst->hasOneUse() &&
               FastIS->tryToFoldLoad(cast<LoadInst>(BeforeInst), Inst)) {
             // If we succeeded, don't re-select the load.
             BI = std::next(BasicBlock::const_iterator(BeforeInst));
             --NumFastIselRemaining;
             ++NumFastIselSuccess;
           }
           continue;
         }
 
+        FastISelFailed = true;
+
         // Then handle certain instructions as single-LLVM-Instruction blocks.
         if (isa<CallInst>(Inst)) {
           OptimizationRemarkMissed R("sdagisel", "FastISelFailure",
                                      Inst->getDebugLoc(), LLVMBB);
 
           R << "FastISel missed call";
 
           if (R.isEnabled() || EnableFastISelAbort) {