[InstCombine, SCCP] Consolidate code used to remove instructions

InstCombine and SCCP both want to remove dead code in a very particular
way but using identical means to do so.  Share the code between the two.

No functionality change is intended.

llvm-svn: 258653

3 files changed, 26 insertions, 37 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 0ccd79a5cef..329a1f1af89 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3012,24 +3012,9 @@ static bool prepareICWorklistFromFunction(Function &F, const DataLayout &DL,
     if (Visited.count(&*BB))
       continue;
 
-    // Delete the instructions backwards, as it has a reduced likelihood of
-    // having to update as many def-use and use-def chains.
-    Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
-    while (EndInst != BB->begin()) {
-      // Delete the next to last instruction.
-      Instruction *Inst = &*--EndInst->getIterator();
-      if (!Inst->use_empty() && !Inst->getType()->isTokenTy())
-        Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
-      if (Inst->isEHPad() || Inst->getType()->isTokenTy()) {
-        EndInst = Inst;
-        continue;
-      }
-      if (!isa<DbgInfoIntrinsic>(Inst)) {
-        ++NumDeadInst;
-        MadeIRChange = true;
-      }
-      Inst->eraseFromParent();
-    }
+    unsigned NumDeadInstInBB = removeAllNonTerminatorAndEHPadInstructions(&*BB);
+    MadeIRChange |= NumDeadInstInBB > 0;
+    NumDeadInst += NumDeadInstInBB;
   }
 
   return MadeIRChange;
diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp
index 4b18679a9c4..902fbdfc295 100644
--- a/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -1568,25 +1568,8 @@ static void DeleteInstructionInBlock(BasicBlock *BB) {
   DEBUG(dbgs() << "  BasicBlock Dead:" << *BB);
   ++NumDeadBlocks;
 
-  // Check to see if there are non-terminating instructions to delete.
-  if (isa<TerminatorInst>(BB->begin()))
-    return;
-
-  // Delete the instructions backwards, as it has a reduced likelihood of having
-  // to update as many def-use and use-def chains.
-  Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
-  while (EndInst != BB->begin()) {
-    // Delete the next to last instruction.
-    Instruction *Inst = &*--EndInst->getIterator();
-    if (!Inst->use_empty())
-      Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
-    if (Inst->isEHPad()) {
-      EndInst = Inst;
-      continue;
-    }
-    BB->getInstList().erase(Inst);
-    ++NumInstRemoved;
-  }
+  unsigned NumRemovedInBB = removeAllNonTerminatorAndEHPadInstructions(BB);
+  NumInstRemoved += NumRemovedInBB;
 }
 
 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index ed941a7d61a..d2ac9890b62 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1222,6 +1222,27 @@ bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
                            Deref, Offset);
 }
 
+unsigned llvm::removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB) {
+  unsigned NumDeadInst = 0;
+  // Delete the instructions backwards, as it has a reduced likelihood of
+  // having to update as many def-use and use-def chains.
+  Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
+  while (EndInst != BB->begin()) {
+    // Delete the next to last instruction.
+    Instruction *Inst = &*--EndInst->getIterator();
+    if (!Inst->use_empty() && !Inst->getType()->isTokenTy())
+      Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
+    if (Inst->isEHPad() || Inst->getType()->isTokenTy()) {
+      EndInst = Inst;
+      continue;
+    }
+    if (!isa<DbgInfoIntrinsic>(Inst))
+      ++NumDeadInst;
+    Inst->eraseFromParent();
+  }
+  return NumDeadInst;
+}
+
 void llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
   BasicBlock *BB = I->getParent();
   // Loop over all of the successors, removing BB's entry from any PHI