Vendor import of llvm trunk r240225:vendor/llvm/llvm-trunk-r240225

https://llvm.org/svn/llvm-project/llvm/trunk@240225

1 files changed, 20 insertions, 2 deletions

diff --git a/lib/Transforms/IPO/ArgumentPromotion.cpp b/lib/Transforms/IPO/ArgumentPromotion.cpp
index c7c57ab56444..86b3faa09b9c 100644
--- a/lib/Transforms/IPO/ArgumentPromotion.cpp
+++ b/lib/Transforms/IPO/ArgumentPromotion.cpp
@@ -92,7 +92,7 @@ namespace {
     unsigned maxElements;
     DenseMap<const Function *, DISubprogram *> FunctionDIs;
   };
-}
+} // namespace
 
 char ArgPromotion::ID = 0;
 INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion",
@@ -245,6 +245,24 @@ CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
     Argument *PtrArg = PointerArgs[i];
     Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
 
+    // Replace sret attribute with noalias. This reduces register pressure by
+    // avoiding a register copy.
+    if (PtrArg->hasStructRetAttr()) {
+      unsigned ArgNo = PtrArg->getArgNo();
+      F->setAttributes(
+          F->getAttributes()
+              .removeAttribute(F->getContext(), ArgNo + 1, Attribute::StructRet)
+              .addAttribute(F->getContext(), ArgNo + 1, Attribute::NoAlias));
+      for (Use &U : F->uses()) {
+        CallSite CS(U.getUser());
+        CS.setAttributes(
+            CS.getAttributes()
+                .removeAttribute(F->getContext(), ArgNo + 1,
+                                 Attribute::StructRet)
+                .addAttribute(F->getContext(), ArgNo + 1, Attribute::NoAlias));
+      }
+    }
+
     // If this is a byval argument, and if the aggregate type is small, just
     // pass the elements, which is always safe, if the passed value is densely
     // packed or if we can prove the padding bytes are never accessed. This does
@@ -553,7 +571,7 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg,
     LoadInst *Load = Loads[i];
     BasicBlock *BB = Load->getParent();
 
-    AliasAnalysis::Location Loc = MemoryLocation::get(Load);
+    MemoryLocation Loc = MemoryLocation::get(Load);
     if (AA.canInstructionRangeModRef(BB->front(), *Load, Loc,
         AliasAnalysis::Mod))
       return false;  // Pointer is invalidated!