[llvm] [DSE] Apply initializes attribute to DSE (PR #107282)

[Haopeng Liu via llvm-commits]

================
@@ -820,20 +828,121 @@ struct MemoryLocationWrapper {
   const Value *UnderlyingObject;
   MemoryDef *MemDef;
   Instruction *DefInst;
+  bool DefByInitializesAttr = false;
 };
 
 // A memory def wrapper that represents a MemoryDef and the MemoryLocation(s)
 // defined by this MemoryDef.
 struct MemoryDefWrapper {
-  MemoryDefWrapper(MemoryDef *MemDef, std::optional<MemoryLocation> MemLoc) {
+  MemoryDefWrapper(
+      MemoryDef *MemDef,
+      const SmallVectorImpl<std::pair<MemoryLocation, bool>> &MemLocations) {
     DefInst = MemDef->getMemoryInst();
-    if (MemLoc.has_value())
-      DefinedLocation = MemoryLocationWrapper(*MemLoc, MemDef);
+    for (auto &[MemLoc, DefByInitializesAttr] : MemLocations)
+      DefinedLocations.push_back(
+          MemoryLocationWrapper(MemLoc, MemDef, DefByInitializesAttr));
   }
   Instruction *DefInst;
-  std::optional<MemoryLocationWrapper> DefinedLocation = std::nullopt;
+  SmallVector<MemoryLocationWrapper, 1> DefinedLocations;
+};
+
+bool HasInitializesAttr(Instruction *I) {
+  CallBase *CB = dyn_cast<CallBase>(I);
+  if (!CB)
+    return false;
+
+  for (size_t Idx = 0; Idx < CB->arg_size(); Idx++)
+    if (CB->paramHasAttr(Idx, Attribute::Initializes))
+      return true;
+  return false;
+}
+
+struct ArgumentInitInfo {
+  size_t Idx = -1;
+  ConstantRangeList Inits;
+  bool HasDeadOnUnwindAttr = false;
+  bool FuncHasNoUnwindAttr = false;
 };
 
+ConstantRangeList
+GetMergedInitAttr(const SmallVectorImpl<ArgumentInitInfo> &Args) {
+  if (Args.empty())
+    return {};
+
+  // To address unwind, the function should have nounwind attribute or the
+  // arguments have dead_on_unwind attribute. Otherwise, return empty.
+  for (const auto &Arg : Args) {
+    if (!Arg.FuncHasNoUnwindAttr && !Arg.HasDeadOnUnwindAttr)
+      return {};
+    if (Arg.Inits.empty())
+      return {};
+  }
+
+  if (Args.size() == 1)
+    return Args[0].Inits;
+
+  ConstantRangeList MergedIntervals = Args[0].Inits;
+  for (size_t i = 1; i < Args.size(); i++)
----------------
haopliu wrote:

Thanks for this info! Will keep these style rules in mind.

https://github.com/llvm/llvm-project/pull/107282