Reapply [MergeICmps] Don't require GEP

Recommit without changes over 53abe3ff66a54117308352d379837c7d3229f8d6,
which addressed the cause of the reported crash.

-----

With opaque pointers, the zero-offset load will generally not use
a GEP. Allow a direct load without GEP, which is treated the same
way as a zero-offset GEP.

1 files changed, 32 insertions, 20 deletions

diff --git a/llvm/lib/Transforms/Scalar/MergeICmps.cpp b/llvm/lib/Transforms/Scalar/MergeICmps.cpp
index 1c1026b097f8..ce01ae5b2692 100644
--- a/llvm/lib/Transforms/Scalar/MergeICmps.cpp
+++ b/llvm/lib/Transforms/Scalar/MergeICmps.cpp
@@ -144,31 +144,33 @@ BCEAtom visitICmpLoadOperand(Value *const Val, BaseIdentifier &BaseId) {
     LLVM_DEBUG(dbgs() << "volatile or atomic\n");
     return {};
   }
-  Value *const Addr = LoadI->getOperand(0);
+  Value *Addr = LoadI->getOperand(0);
   if (Addr->getType()->getPointerAddressSpace() != 0) {
     LLVM_DEBUG(dbgs() << "from non-zero AddressSpace\n");
     return {};
   }
-  auto *const GEP = dyn_cast<GetElementPtrInst>(Addr);
-  if (!GEP)
-    return {};
-  LLVM_DEBUG(dbgs() << "GEP\n");
-  if (GEP->isUsedOutsideOfBlock(LoadI->getParent())) {
-    LLVM_DEBUG(dbgs() << "used outside of block\n");
-    return {};
-  }
-  const auto &DL = GEP->getModule()->getDataLayout();
-  if (!isDereferenceablePointer(GEP, LoadI->getType(), DL)) {
+  const auto &DL = LoadI->getModule()->getDataLayout();
+  if (!isDereferenceablePointer(Addr, LoadI->getType(), DL)) {
     LLVM_DEBUG(dbgs() << "not dereferenceable\n");
     // We need to make sure that we can do comparison in any order, so we
     // require memory to be unconditionnally dereferencable.
     return {};
   }
-  APInt Offset = APInt(DL.getPointerTypeSizeInBits(GEP->getType()), 0);
-  if (!GEP->accumulateConstantOffset(DL, Offset))
-    return {};
-  return BCEAtom(GEP, LoadI, BaseId.getBaseId(GEP->getPointerOperand()),
-                 Offset);
+
+  APInt Offset = APInt(DL.getPointerTypeSizeInBits(Addr->getType()), 0);
+  Value *Base = Addr;
+  auto *GEP = dyn_cast<GetElementPtrInst>(Addr);
+  if (GEP) {
+    LLVM_DEBUG(dbgs() << "GEP\n");
+    if (GEP->isUsedOutsideOfBlock(LoadI->getParent())) {
+      LLVM_DEBUG(dbgs() << "used outside of block\n");
+      return {};
+    }
+    if (!GEP->accumulateConstantOffset(DL, Offset))
+      return {};
+    Base = GEP->getPointerOperand();
+  }
+  return BCEAtom(GEP, LoadI, BaseId.getBaseId(Base), Offset);
 }
 
 // A comparison between two BCE atoms, e.g. `a == o.a` in the example at the
@@ -367,8 +369,11 @@ Optional<BCECmpBlock> visitCmpBlock(Value *const Val, BasicBlock *const Block,
     return None;
 
   BCECmpBlock::InstructionSet BlockInsts(
-      {Result->Lhs.GEP, Result->Rhs.GEP, Result->Lhs.LoadI, Result->Rhs.LoadI,
-       Result->CmpI, BranchI});
+      {Result->Lhs.LoadI, Result->Rhs.LoadI, Result->CmpI, BranchI});
+  if (Result->Lhs.GEP)
+    BlockInsts.insert(Result->Lhs.GEP);
+  if (Result->Rhs.GEP)
+    BlockInsts.insert(Result->Rhs.GEP);
   return BCECmpBlock(std::move(*Result), Block, BlockInsts);
 }
 
@@ -603,8 +608,15 @@ static BasicBlock *mergeComparisons(ArrayRef<BCECmpBlock> Comparisons,
                          NextCmpBlock->getParent(), InsertBefore);
   IRBuilder<> Builder(BB);
   // Add the GEPs from the first BCECmpBlock.
-  Value *const Lhs = Builder.Insert(FirstCmp.Lhs().GEP->clone());
-  Value *const Rhs = Builder.Insert(FirstCmp.Rhs().GEP->clone());
+  Value *Lhs, *Rhs;
+  if (FirstCmp.Lhs().GEP)
+    Lhs = Builder.Insert(FirstCmp.Lhs().GEP->clone());
+  else
+    Lhs = FirstCmp.Lhs().LoadI->getPointerOperand();
+  if (FirstCmp.Rhs().GEP)
+    Rhs = Builder.Insert(FirstCmp.Rhs().GEP->clone());
+  else
+    Rhs = FirstCmp.Rhs().LoadI->getPointerOperand();
 
   Value *IsEqual = nullptr;
   LLVM_DEBUG(dbgs() << "Merging " << Comparisons.size() << " comparisons -> "