[NFC][SimplifyCFG] FoldTwoEntryPHINode(): make better use of GetIfCondition() returning dom block

Author: LebedevRI

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -2794,13 +2794,12 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
   // in the predecessor blocks can be promoted as well. If not, we won't be able
   // to get rid of the control flow, so it's not worth promoting to select
   // instructions.
-  BasicBlock *DomBlock = nullptr;
+  BasicBlock *DomBlock = DomBI->getParent();
   BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
   BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
   if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
     IfBlock1 = nullptr;
   } else {
-    DomBlock = *pred_begin(IfBlock1);
     for (BasicBlock::iterator I = IfBlock1->begin(); !I->isTerminator(); ++I)
       if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I) &&
           !isa<PseudoProbeInst>(I)) {
@@ -2814,7 +2813,6 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
   if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
     IfBlock2 = nullptr;
   } else {
-    DomBlock = *pred_begin(IfBlock2);
     for (BasicBlock::iterator I = IfBlock2->begin(); !I->isTerminator(); ++I)
       if (!AggressiveInsts.count(&*I) && !isa<DbgInfoIntrinsic>(I) &&
           !isa<PseudoProbeInst>(I)) {
@@ -2824,7 +2822,6 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
         return Changed;
       }
   }
-  assert(DomBlock && "Failed to find root DomBlock");
 
   // If either of the blocks has it's address taken, we can't do this fold.
   if ((IfBlock1 && IfBlock1->hasAddressTaken()) ||
@@ -2837,16 +2834,15 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
 
   // If we can still promote the PHI nodes after this gauntlet of tests,
   // do all of the PHI's now.
-  Instruction *InsertPt = DomBlock->getTerminator();
-  IRBuilder<NoFolder> Builder(InsertPt);
 
   // Move all 'aggressive' instructions, which are defined in the
   // conditional parts of the if's up to the dominating block.
   if (IfBlock1)
-    hoistAllInstructionsInto(DomBlock, InsertPt, IfBlock1);
+    hoistAllInstructionsInto(DomBlock, DomBI, IfBlock1);
   if (IfBlock2)
-    hoistAllInstructionsInto(DomBlock, InsertPt, IfBlock2);
+    hoistAllInstructionsInto(DomBlock, DomBI, IfBlock2);
 
+  IRBuilder<NoFolder> Builder(DomBI);
   // Propagate fast-math-flags from phi nodes to replacement selects.
   IRBuilder<>::FastMathFlagGuard FMFGuard(Builder);
   while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
@@ -2857,7 +2853,7 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
     Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
     Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
 
-    Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", InsertPt);
+    Value *Sel = Builder.CreateSelect(IfCond, TrueVal, FalseVal, "", DomBI);
     PN->replaceAllUsesWith(Sel);
     Sel->takeName(PN);
     PN->eraseFromParent();
@@ -2866,8 +2862,6 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
   // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
   // has been flattened.  Change DomBlock to jump directly to our new block to
   // avoid other simplifycfg's kicking in on the diamond.
-  Instruction *OldTI = DomBlock->getTerminator();
-  Builder.SetInsertPoint(OldTI);
   Builder.CreateBr(BB);
 
   SmallVector<DominatorTree::UpdateType, 3> Updates;
@@ -2877,7 +2871,7 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
       Updates.push_back({DominatorTree::Delete, DomBlock, Successor});
   }
 
-  OldTI->eraseFromParent();
+  DomBI->eraseFromParent();
   if (DTU)
     DTU->applyUpdates(Updates);