Add CodeGen support for functions that always return arguments via a new parameter attribute 'returned', which is taken advantage of in target-independent tail call opportunity detection and in ARM call lowering (when placed on an integral first parameter).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179925 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 37 insertions, 7 deletions

diff --git a/lib/CodeGen/Analysis.cpp b/lib/CodeGen/Analysis.cpp
index 9723f8080c..4731af5089 100644
--- a/lib/CodeGen/Analysis.cpp
+++ b/lib/CodeGen/Analysis.cpp
@@ -261,6 +261,32 @@ static bool sameNoopInput(const Value *V1, const Value *V2,
             TLI.getPointerTy().getSizeInBits() == 
               cast<IntegerType>(I->getType())->getBitWidth())
           NoopInput = Op;
+      } else if (isa<CallInst>(I)) {
+        // Look through call
+        for (User::const_op_iterator i = I->op_begin(),
+                                     // Skip Callee
+                                     e = I->op_end() - 1;
+             i != e; ++i) {
+          unsigned attrInd = i - I->op_begin() + 1;
+          if (cast<CallInst>(I)->paramHasAttr(attrInd, Attribute::Returned) &&
+              isNoopBitcast((*i)->getType(), I->getType(), TLI)) {
+            NoopInput = *i;
+            break;
+          }
+        }
+      } else if (isa<InvokeInst>(I)) {
+        // Look through invoke
+        for (User::const_op_iterator i = I->op_begin(),
+                                     // Skip BB, BB, Callee
+                                     e = I->op_end() - 3;
+             i != e; ++i) {
+          unsigned attrInd = i - I->op_begin() + 1;
+          if (cast<InvokeInst>(I)->paramHasAttr(attrInd, Attribute::Returned) &&
+              isNoopBitcast((*i)->getType(), I->getType(), TLI)) {
+            NoopInput = *i;
+            break;
+          }
+        }
       }
     }
 
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index ce40cd6a0c..c1c8be4387 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5232,6 +5232,7 @@ void SelectionDAGBuilder::LowerCallTo(ImmutableCallSite CS, SDValue Callee,
     Entry.isSRet = true;
     Entry.isNest = false;
     Entry.isByVal = false;
+    Entry.isReturned = false;
     Entry.Alignment = Align;
     Args.push_back(Entry);
     RetTy = Type::getVoidTy(FTy->getContext());
@@ -5249,13 +5250,14 @@ void SelectionDAGBuilder::LowerCallTo(ImmutableCallSite CS, SDValue Callee,
     Entry.Node = ArgNode; Entry.Ty = V->getType();
 
     unsigned attrInd = i - CS.arg_begin() + 1;
-    Entry.isSExt  = CS.paramHasAttr(attrInd, Attribute::SExt);
-    Entry.isZExt  = CS.paramHasAttr(attrInd, Attribute::ZExt);
-    Entry.isInReg = CS.paramHasAttr(attrInd, Attribute::InReg);
-    Entry.isSRet  = CS.paramHasAttr(attrInd, Attribute::StructRet);
-    Entry.isNest  = CS.paramHasAttr(attrInd, Attribute::Nest);
-    Entry.isByVal = CS.paramHasAttr(attrInd, Attribute::ByVal);
-    Entry.Alignment = CS.getParamAlignment(attrInd);
+    Entry.isSExt     = CS.paramHasAttr(attrInd, Attribute::SExt);
+    Entry.isZExt     = CS.paramHasAttr(attrInd, Attribute::ZExt);
+    Entry.isInReg    = CS.paramHasAttr(attrInd, Attribute::InReg);
+    Entry.isSRet     = CS.paramHasAttr(attrInd, Attribute::StructRet);
+    Entry.isNest     = CS.paramHasAttr(attrInd, Attribute::Nest);
+    Entry.isByVal    = CS.paramHasAttr(attrInd, Attribute::ByVal);
+    Entry.isReturned = CS.paramHasAttr(attrInd, Attribute::Returned);
+    Entry.Alignment  = CS.getParamAlignment(attrInd);
     Args.push_back(Entry);
   }
 
@@ -6430,6 +6432,8 @@ TargetLowering::LowerCallTo(TargetLowering::CallLoweringInfo &CLI) const {
       }
       if (Args[i].isNest)
         Flags.setNest();
+      if (Args[i].isReturned)
+        Flags.setReturned();
       Flags.setOrigAlign(OriginalAlignment);
 
       MVT PartVT = getRegisterType(CLI.RetTy->getContext(), VT);