[SimplifyCFG] Use a more generic name for the selects created by SpeculativelyExecuteBB to prevent long names from being created

[craig.topper]

Summary

Currently the selects are created with the names of their inputs concatenated together. It's possible to get cases that chain these selects together resulting in long names due to multiple levels of concatenation. Our internal branch of llvm managed to generate names over 100000 characters in length on a particular test due to an extreme compounding of the names.

This patch changes the name to a generic name that is not dependent on its inputs. I'm open to other suggestions.

As a small demonstration, here is what is currently in the output IR for merge-cond-stores-2.ll before this patch

%1 = select i1 %tobool, i32 %0, i32 %or
%.or4 = select i1 %tobool2, i32 %1, i32 %or4
%.or4.or9 = select i1 %tobool7, i32 %.or4, i32 %or9
%.or4.or9.or14 = select i1 %tobool12, i32 %.or4.or9, i32 %or14
%.or4.or9.or14.or19 = select i1 %tobool17, i32 %.or4.or9.or14, i32 %or19
%.or4.or9.or14.or19.or24 = select i1 %tobool22, i32 %.or4.or9.or14.or19, i32 %or24
%.or4.or9.or14.or19.or24.or29 = select i1 %tobool27, i32 %.or4.or9.or14.or19.or24, i32 %or29
%.or4.or9.or14.or19.or24.or29.or34 = select i1 %tobool32, i32 %.or4.or9.or14.or19.or24.or29, i32 %or34
%.or4.or9.or14.or19.or24.or29.or34.or39 = select i1 %tobool37, i32 %.or4.or9.or14.or19.or24.or29.or34, i32 %or39
%.or4.or9.or14.or19.or24.or29.or34.or39.or44 = select i1 %tobool42, i32 %.or4.or9.or14.or19.or24.or29.or34.or39, i32 %or44
%.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49 = select i1 %tobool47, i32 %.or4.or9.or14.or19.or24.or29.or34.or39.or44, i32 %or49
%.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54 = select i1 %tobool52, i32 %.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49, i32 %or54
%.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54.or59 = select i1 %tobool57, i32 %.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54, i32 %or59
%.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54.or59.or64 = select i1 %tobool62, i32 %.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54.or59, i32 %or64
%.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54.or59.or64.or69 = select i1 %tobool67, i32 %.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54.or59.or64, i32 %or69
%.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54.or59.or64.or69.or74 = select i1 %tobool72, i32 %.or4.or9.or14.or19.or24.or29.or34.or39.or44.or49.or54.or59.or64.or69, i32 %or74

[spatel]

The code change looks obviously correct, so LGTM.

I'd suggest regenerating the checks in the tests using utils/update_test_checks.py. We really don't want those to be affected by cosmetic name changes, right?

llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp

static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
   // Insert a select of the value of the speculated store.
   if (SpeculatedStoreValue) {
     IRBuilder<NoFolder> Builder(BI);
     Value *TrueV = SpeculatedStore->getValueOperand();
     Value *FalseV = SpeculatedStoreValue;
     if (Invert)
       std::swap(TrueV, FalseV);
     Value *S = Builder.CreateSelect(
-        BrCond, TrueV, FalseV, TrueV->getName() + "." + FalseV->getName(), BI);
+        BrCond, TrueV, FalseV, "spec.store.select", BI);
     SpeculatedStore->setOperand(0, S);
     SpeculatedStore->applyMergedLocation(BI->getDebugLoc(),
                                          SpeculatedStore->getDebugLoc());
   }
 
   // Metadata can be dependent on the condition we are hoisting above.
   // Conservatively strip all metadata on the instruction.
   for (auto &I : *ThenBB)
for (BasicBlock::iterator I = EndBB->begin();
 
     // Create a select whose true value is the speculatively executed value and
     // false value is the preexisting value. Swap them if the branch
     // destinations were inverted.
     Value *TrueV = ThenV, *FalseV = OrigV;
     if (Invert)
       std::swap(TrueV, FalseV);
     Value *V = Builder.CreateSelect(
-        BrCond, TrueV, FalseV, TrueV->getName() + "." + FalseV->getName(), BI);
+        BrCond, TrueV, FalseV, "spec.select", BI);
     PN->setIncomingValue(OrigI, V);
     PN->setIncomingValue(ThenI, V);
   }
 
   ++NumSpeculations;
   return true;
 }