Revert "LSV: forbid load-cycles when vectorizing; fix bug (#104815)" (#106245)

This reverts commit c46b41a.

Multiple tests time out, either due to performance hit (see comment) or
a cycle.

Author: dklimkin

llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp

@@ -998,32 +998,10 @@ bool Vectorizer::isSafeToMove(
   LLVM_DEBUG(dbgs() << "LSV: isSafeToMove(" << *ChainElem << " -> "
                     << *ChainBegin << ")\n");
 
-  assert(isa<LoadInst>(ChainElem) == IsLoadChain &&
-         isa<LoadInst>(ChainBegin) == IsLoadChain);
-
+  assert(isa<LoadInst>(ChainElem) == IsLoadChain);
   if (ChainElem == ChainBegin)
     return true;
 
-  if constexpr (IsLoadChain) {
-    // If ChainElem depends on ChainBegin, they're not safe to reorder.
-    SmallVector<Instruction *, 8> Worklist;
-    Worklist.emplace_back(ChainElem);
-    while (!Worklist.empty()) {
-      Instruction *I = Worklist.pop_back_val();
-      for (Use &O : I->operands()) {
-        if (isa<PHINode>(O))
-          continue;
-        if (auto *J = dyn_cast<Instruction>(O)) {
-          if (J == ChainBegin) {
-            LLVM_DEBUG(dbgs() << "LSV: dependent loads; not safe to reorder\n");
-            return false;
-          }
-          Worklist.emplace_back(J);
-        }
-      }
-    }
-  }
-
   // Invariant loads can always be reordered; by definition they are not
   // clobbered by stores.
   if (isInvariantLoad(ChainElem))

llvm/test/Transforms/LoadStoreVectorizer/AArch64/pr37865.ll

@@ -1,22 +1,9 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
-; RUN: opt -mtriple=aarch64 -passes=load-store-vectorizer -S %s | FileCheck %s
-
-; LSV was attempting to vectorize this earlier, but crashed while re-ordering
-; instructions due to the load-load cycle. Now, the candidate loads are no
-; longer considered safe for reordering.
+; REQUIRES: asserts
+; RUN: not --crash opt -mtriple=aarch64 -passes=load-store-vectorizer \
+; RUN:   -disable-output %s 2>&1 | FileCheck %s
 
 define i32 @load_cycle(ptr %x) {
-; CHECK-LABEL: define i32 @load_cycle(
-; CHECK-SAME: ptr [[X:%.*]]) {
-; CHECK-NEXT:  [[ENTRY:.*:]]
-; CHECK-NEXT:    [[GEP_X_1:%.*]] = getelementptr inbounds [2 x i32], ptr [[X]], i32 0, i32 1
-; CHECK-NEXT:    [[LOAD_X_1:%.*]] = load i32, ptr [[GEP_X_1]], align 4
-; CHECK-NEXT:    [[REM:%.*]] = urem i32 [[LOAD_X_1]], 1
-; CHECK-NEXT:    [[GEP_X_2:%.*]] = getelementptr inbounds [2 x i32], ptr [[X]], i32 [[REM]], i32 0
-; CHECK-NEXT:    [[LOAD_X_2:%.*]] = load i32, ptr [[GEP_X_2]], align 4
-; CHECK-NEXT:    [[RET:%.*]] = add i32 [[LOAD_X_2]], [[LOAD_X_1]]
-; CHECK-NEXT:    ret i32 [[RET]]
-;
+; CHECK: Unexpected cycle while re-ordering instructions
 entry:
   %gep.x.1 = getelementptr inbounds [2 x i32], ptr %x, i32 0, i32 1
   %load.x.1 = load i32, ptr %gep.x.1
@@ -26,61 +13,3 @@ entry:
   %ret = add i32 %load.x.2, %load.x.1
   ret i32 %ret
 }
-
-define i32 @load_cycle2(ptr %x, i32 %y) {
-; CHECK-LABEL: define i32 @load_cycle2(
-; CHECK-SAME: ptr [[X:%.*]], i32 [[Y:%.*]]) {
-; CHECK-NEXT:  [[ENTRY:.*:]]
-; CHECK-NEXT:    [[GEP_X_1:%.*]] = getelementptr inbounds [2 x i32], ptr [[X]], i32 [[Y]], i32 1
-; CHECK-NEXT:    [[LOAD_X_1:%.*]] = load i32, ptr [[GEP_X_1]], align 4
-; CHECK-NEXT:    [[MUL:%.*]] = mul i32 [[LOAD_X_1]], 2
-; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[Y]], [[MUL]]
-; CHECK-NEXT:    [[SUB_1:%.*]] = sub i32 [[ADD]], [[LOAD_X_1]]
-; CHECK-NEXT:    [[SUB_2:%.*]] = sub i32 [[SUB_1]], [[LOAD_X_1]]
-; CHECK-NEXT:    [[GEP_X_2:%.*]] = getelementptr inbounds [2 x i32], ptr [[X]], i32 [[SUB_2]], i32 0
-; CHECK-NEXT:    [[LOAD_X_2:%.*]] = load i32, ptr [[GEP_X_2]], align 4
-; CHECK-NEXT:    [[RET:%.*]] = add i32 [[LOAD_X_2]], [[LOAD_X_1]]
-; CHECK-NEXT:    ret i32 [[RET]]
-;
-entry:
-  %gep.x.1 = getelementptr inbounds [2 x i32], ptr %x, i32 %y, i32 1
-  %load.x.1 = load i32, ptr %gep.x.1
-  %mul = mul i32 %load.x.1, 2
-  %add = add i32 %y, %mul
-  %sub.1 = sub i32 %add, %load.x.1
-  %sub.2 = sub i32 %sub.1, %load.x.1
-  %gep.x.2 = getelementptr inbounds [2 x i32], ptr %x, i32 %sub.2, i32 0
-  %load.x.2 = load i32, ptr %gep.x.2
-  %ret = add i32 %load.x.2, %load.x.1
-  ret i32 %ret
-}
-
-@global.1 = global i32 0
-@global.2 = global [1 x [3 x i32]] zeroinitializer
-
-define i16 @load_cycle3() {
-; CHECK-LABEL: define i16 @load_cycle3() {
-; CHECK-NEXT:  [[ENTRY:.*:]]
-; CHECK-NEXT:    [[LOAD_1:%.*]] = load i32, ptr @global.1, align 4
-; CHECK-NEXT:    [[UREM_1:%.*]] = urem i32 [[LOAD_1]], 1
-; CHECK-NEXT:    [[GEP_1:%.*]] = getelementptr inbounds [1 x [3 x i32]], ptr @global.2, i32 0, i32 [[UREM_1]]
-; CHECK-NEXT:    [[GEP_2:%.*]] = getelementptr inbounds [3 x i32], ptr [[GEP_1]], i32 0, i32 2
-; CHECK-NEXT:    [[LOAD_2:%.*]] = load i32, ptr [[GEP_2]], align 4
-; CHECK-NEXT:    [[UREM_2:%.*]] = urem i32 [[LOAD_2]], 1
-; CHECK-NEXT:    [[GEP_3:%.*]] = getelementptr inbounds [1 x [3 x i32]], ptr @global.2, i32 0, i32 [[UREM_2]]
-; CHECK-NEXT:    [[GEP_4:%.*]] = getelementptr inbounds [3 x i32], ptr [[GEP_3]], i32 0, i32 1
-; CHECK-NEXT:    [[LOAD_3:%.*]] = load i32, ptr [[GEP_4]], align 4
-; CHECK-NEXT:    ret i16 0
-;
-entry:
-  %load.1 = load i32, ptr @global.1
-  %urem.1 = urem i32 %load.1, 1
-  %gep.1 = getelementptr inbounds [1 x [3 x i32]], ptr @global.2, i32 0, i32 %urem.1
-  %gep.2 = getelementptr inbounds [3 x i32], ptr %gep.1, i32 0, i32 2
-  %load.2 = load i32, ptr %gep.2
-  %urem.2 = urem i32 %load.2, 1
-  %gep.3 = getelementptr inbounds [1 x [3 x i32]], ptr @global.2, i32 0, i32 %urem.2
-  %gep.4 = getelementptr inbounds [3 x i32], ptr %gep.3, i32 0, i32 1
-  %load.3 = load i32, ptr %gep.4
-  ret i16 0
-}