[AggressiveInstCombine] Fix memory location for alias analysis

Author: dtcxzyw

llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp

@@ -710,9 +710,17 @@ static bool foldLoadsRecursive(Value *V, LoadOps &LOps, const DataLayout &DL,
   MemoryLocation Loc;
   if (!Start->comesBefore(End)) {
     std::swap(Start, End);
-    Loc = MemoryLocation::get(End);
+    // If LOps.RootInsert comes after LI2, since we use LI2 as the new insert
+    // point, we should make sure whether the memory region accessed by LOps
+    // isn't modified.
     if (LOps.FoundRoot)
-      Loc = Loc.getWithNewSize(LOps.LoadSize);
+      Loc = MemoryLocation(
+          LOps.Root->getPointerOperand(),
+          LocationSize::precise(DL.getTypeStoreSize(
+              IntegerType::get(LI1->getContext(), LOps.LoadSize))),
+          LOps.AATags);
+    else
+      Loc = MemoryLocation::get(End);
   } else
     Loc = MemoryLocation::get(End);
   unsigned NumScanned = 0;

llvm/test/Transforms/AggressiveInstCombine/X86/or-load.ll

@@ -2512,8 +2512,14 @@ entry:
 define i64 @loadcombine_consecutive_mayalias(ptr %p) {
 ; LE-LABEL: @loadcombine_consecutive_mayalias(
 ; LE-NEXT:  entry:
-; LE-NEXT:    [[LOAD1:%.*]] = load i64, ptr [[P:%.*]], align 4
+; LE-NEXT:    [[LOAD3:%.*]] = load i32, ptr [[P:%.*]], align 4
+; LE-NEXT:    [[GEP1:%.*]] = getelementptr i8, ptr [[P]], i64 4
 ; LE-NEXT:    store i8 0, ptr getelementptr inbounds nuw (i8, ptr @g, i64 4), align 4
+; LE-NEXT:    [[LOAD2:%.*]] = load i32, ptr [[GEP1]], align 4
+; LE-NEXT:    [[TMP0:%.*]] = zext i32 [[LOAD2]] to i64
+; LE-NEXT:    [[TMP1:%.*]] = shl i64 [[TMP0]], 32
+; LE-NEXT:    [[ZEXT3:%.*]] = zext i32 [[LOAD3]] to i64
+; LE-NEXT:    [[LOAD1:%.*]] = or i64 [[TMP1]], [[ZEXT3]]
 ; LE-NEXT:    [[RES:%.*]] = lshr i64 [[LOAD1]], 32
 ; LE-NEXT:    ret i64 [[RES]]
 ;