Reapply [MergeICmps] Don't require GEP

Recommit without changes over 53abe3ff66,
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.

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 -> "

llvm/test/Transforms/MergeICmps/X86/no-gep-other-work.ll

@@ -10,22 +10,13 @@ declare void @other_work()
 
 define i1 @test(i8* dereferenceable(2) %arg, i8* dereferenceable(2) %arg1) {
 ; CHECK-LABEL: @test(
-; CHECK-NEXT:  entry:
+; CHECK-NEXT:  "if+entry":
 ; CHECK-NEXT:    call void @other_work()
-; CHECK-NEXT:    [[ARG_OFF:%.*]] = getelementptr inbounds i8, i8* [[ARG:%.*]], i64 1
-; CHECK-NEXT:    [[ARG1_OFF:%.*]] = getelementptr inbounds i8, i8* [[ARG1:%.*]], i64 1
-; CHECK-NEXT:    [[ARG_OFF_VAL:%.*]] = load i8, i8* [[ARG_OFF]], align 1
-; CHECK-NEXT:    [[ARG1_OFF_VAL:%.*]] = load i8, i8* [[ARG1_OFF]], align 1
-; CHECK-NEXT:    [[CMP_OFF:%.*]] = icmp eq i8 [[ARG_OFF_VAL]], [[ARG1_OFF_VAL]]
-; CHECK-NEXT:    br i1 [[CMP_OFF]], label [[IF:%.*]], label [[JOIN:%.*]]
-; CHECK:       if:
-; CHECK-NEXT:    [[ARG_VAL:%.*]] = load i8, i8* [[ARG]], align 1
-; CHECK-NEXT:    [[ARG1_VAL:%.*]] = load i8, i8* [[ARG1]], align 1
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[ARG_VAL]], [[ARG1_VAL]]
-; CHECK-NEXT:    br label [[JOIN]]
+; CHECK-NEXT:    [[MEMCMP:%.*]] = call i32 @memcmp(i8* [[ARG:%.*]], i8* [[ARG1:%.*]], i64 2)
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp eq i32 [[MEMCMP]], 0
+; CHECK-NEXT:    br label [[JOIN:%.*]]
 ; CHECK:       join:
-; CHECK-NEXT:    [[PHI:%.*]] = phi i1 [ false, [[ENTRY:%.*]] ], [ [[CMP]], [[IF]] ]
-; CHECK-NEXT:    ret i1 [[PHI]]
+; CHECK-NEXT:    ret i1 [[TMP0]]
 ;
 entry:
   call void @other_work()

llvm/test/Transforms/MergeICmps/X86/opaque-ptr.ll

@@ -7,21 +7,12 @@ target triple = "x86_64-unknown-unknown"
 
 define i1 @test(ptr dereferenceable(8) %a, ptr dereferenceable(8) %b) {
 ; CHECK-LABEL: @test(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[V0:%.*]] = load i32, ptr [[A:%.*]], align 4
-; CHECK-NEXT:    [[V1:%.*]] = load i32, ptr [[B:%.*]], align 4
-; CHECK-NEXT:    [[CMP_I:%.*]] = icmp eq i32 [[V0]], [[V1]]
-; CHECK-NEXT:    br i1 [[CMP_I]], label [[LAND_RHS_I:%.*]], label [[OPEQ1_EXIT:%.*]]
-; CHECK:       land.rhs.i:
-; CHECK-NEXT:    [[SECOND_I:%.*]] = getelementptr inbounds [[S:%.*]], ptr [[A]], i64 0, i32 1
-; CHECK-NEXT:    [[V2:%.*]] = load i32, ptr [[SECOND_I]], align 4
-; CHECK-NEXT:    [[SECOND2_I:%.*]] = getelementptr inbounds [[S]], ptr [[B]], i64 0, i32 1
-; CHECK-NEXT:    [[V3:%.*]] = load i32, ptr [[SECOND2_I]], align 4
-; CHECK-NEXT:    [[CMP3_I:%.*]] = icmp eq i32 [[V2]], [[V3]]
-; CHECK-NEXT:    br label [[OPEQ1_EXIT]]
+; CHECK-NEXT:  "entry+land.rhs.i":
+; CHECK-NEXT:    [[MEMCMP:%.*]] = call i32 @memcmp(ptr [[A:%.*]], ptr [[B:%.*]], i64 8)
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp eq i32 [[MEMCMP]], 0
+; CHECK-NEXT:    br label [[OPEQ1_EXIT:%.*]]
 ; CHECK:       opeq1.exit:
-; CHECK-NEXT:    [[PHI:%.*]] = phi i1 [ false, [[ENTRY:%.*]] ], [ [[CMP3_I]], [[LAND_RHS_I]] ]
-; CHECK-NEXT:    ret i1 [[PHI]]
+; CHECK-NEXT:    ret i1 [[TMP0]]
 ;
 entry:
   %v0 = load i32, ptr %a, align 4