Revert "[InstCombine] avoid crash from deleting an instruction that still has uses (PR43723) (3rd try)"

This reverts commit 3db8a3ef86e7b3331ab466a78c10a62be9e69829.
This caused a different memory-sanitizer failure than earlier attempts,
but it's still not right.

1 files changed, 4 insertions, 18 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 3b137c3f1c3..b1828d0fe32 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2340,21 +2340,13 @@ static bool isAllocSiteRemovable(Instruction *AI,
               return false;
             LLVM_FALLTHROUGH;
           }
+          case Intrinsic::invariant_start:
           case Intrinsic::invariant_end:
           case Intrinsic::lifetime_start:
           case Intrinsic::lifetime_end:
           case Intrinsic::objectsize:
             Users.emplace_back(I);
             continue;
-          case Intrinsic::invariant_start:
-            // Only delete this if it has no uses or a single 'end' use.
-            if (I->use_empty())
-              Users.emplace_back(I);
-            else if (I->hasOneUse() &&
-                     match(I->user_back(),
-                           m_Intrinsic<Intrinsic::invariant_end>()))
-              Users.emplace_back(I);
-            continue;
           }
         }
 
@@ -2402,13 +2394,14 @@ Instruction *InstCombiner::visitAllocSite(Instruction &MI) {
 
   if (isAllocSiteRemovable(&MI, Users, &TLI)) {
     for (unsigned i = 0, e = Users.size(); i != e; ++i) {
+      // Lowering all @llvm.objectsize calls first because they may
+      // use a bitcast/GEP of the alloca we are removing.
       if (!Users[i])
        continue;
 
       Instruction *I = cast<Instruction>(&*Users[i]);
+
       if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
-        // Lowering all @llvm.objectsize calls first because they may
-        // use a bitcast/GEP of the alloca we are removing.
         if (II->getIntrinsicID() == Intrinsic::objectsize) {
           Value *Result =
               lowerObjectSizeCall(II, DL, &TLI, /*MustSucceed=*/true);
@@ -2416,13 +2409,6 @@ Instruction *InstCombiner::visitAllocSite(Instruction &MI) {
           eraseInstFromFunction(*I);
           Users[i] = nullptr; // Skip examining in the next loop.
         }
-        // Erase llvm.invariant.start because we expect that it is used by
-        // llvm.invariant.end that we will remove below.
-        if (II->getIntrinsicID() == Intrinsic::invariant_start) {
-          replaceInstUsesWith(*I, UndefValue::get(I->getType()));
-          eraseInstFromFunction(*I);
-          Users[i] = nullptr; // Skip examining in the next loop.
-        }
       }
     }
     for (unsigned i = 0, e = Users.size(); i != e; ++i) {