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

4 files changed, 35 insertions, 23 deletions

diff --git a/include/llvm/IR/Argument.h b/include/llvm/IR/Argument.h
index ef4e4fc..40d61ff 100644
--- a/include/llvm/IR/Argument.h
+++ b/include/llvm/IR/Argument.h
@@ -78,6 +78,10 @@ public:
   /// containing function.
   bool hasStructRetAttr() const;
 
+  /// \brief Return true if this argument has the returned attribute on it in
+  /// its containing function.
+  bool hasReturnedAttr() const;
+
   /// \brief Add a Attribute to an argument.
   void addAttr(AttributeSet AS);
 
diff --git a/include/llvm/IR/Attributes.h b/include/llvm/IR/Attributes.h
index f93f28b..c801436 100644
--- a/include/llvm/IR/Attributes.h
+++ b/include/llvm/IR/Attributes.h
@@ -87,6 +87,7 @@ public:
     OptimizeForSize,       ///< opt_size
     ReadNone,              ///< Function does not access memory
     ReadOnly,              ///< Function only reads from memory
+    Returned,              ///< Return value is always equal to this argument
     ReturnsTwice,          ///< Function can return twice
     SExt,                  ///< Sign extended before/after call
     StackAlignment,        ///< Alignment of stack for function (3 bits)
diff --git a/include/llvm/Target/TargetCallingConv.h b/include/llvm/Target/TargetCallingConv.h
index 2160e37..56ebfa4 100644
--- a/include/llvm/Target/TargetCallingConv.h
+++ b/include/llvm/Target/TargetCallingConv.h
@@ -36,10 +36,12 @@ namespace ISD {
     static const uint64_t ByValOffs      = 4;
     static const uint64_t Nest           = 1ULL<<5;  ///< Nested fn static chain
     static const uint64_t NestOffs       = 5;
-    static const uint64_t ByValAlign     = 0xFULL << 6; ///< Struct alignment
-    static const uint64_t ByValAlignOffs = 6;
-    static const uint64_t Split          = 1ULL << 10;
-    static const uint64_t SplitOffs      = 10;
+    static const uint64_t Returned       = 1ULL<<6;
+    static const uint64_t ReturnedOffs   = 6;
+    static const uint64_t ByValAlign     = 0xFULL<<7; ///< Struct alignment
+    static const uint64_t ByValAlignOffs = 7;
+    static const uint64_t Split          = 1ULL<<11;
+    static const uint64_t SplitOffs      = 11;
     static const uint64_t OrigAlign      = 0x1FULL<<27;
     static const uint64_t OrigAlignOffs  = 27;
     static const uint64_t ByValSize      = 0xffffffffULL << 32; ///< Struct size
@@ -51,23 +53,26 @@ namespace ISD {
   public:
     ArgFlagsTy() : Flags(0) { }
 
-    bool isZExt()   const { return Flags & ZExt; }
-    void setZExt()  { Flags |= One << ZExtOffs; }
+    bool isZExt()      const { return Flags & ZExt; }
+    void setZExt()     { Flags |= One << ZExtOffs; }
 
-    bool isSExt()   const { return Flags & SExt; }
-    void setSExt()  { Flags |= One << SExtOffs; }
+    bool isSExt()      const { return Flags & SExt; }
+    void setSExt()     { Flags |= One << SExtOffs; }
 
-    bool isInReg()  const { return Flags & InReg; }
-    void setInReg() { Flags |= One << InRegOffs; }
+    bool isInReg()     const { return Flags & InReg; }
+    void setInReg()    { Flags |= One << InRegOffs; }
 
-    bool isSRet()   const { return Flags & SRet; }
-    void setSRet()  { Flags |= One << SRetOffs; }
+    bool isSRet()      const { return Flags & SRet; }
+    void setSRet()     { Flags |= One << SRetOffs; }
 
-    bool isByVal()  const { return Flags & ByVal; }
-    void setByVal() { Flags |= One << ByValOffs; }
+    bool isByVal()     const { return Flags & ByVal; }
+    void setByVal()    { Flags |= One << ByValOffs; }
 
-    bool isNest()   const { return Flags & Nest; }
-    void setNest()  { Flags |= One << NestOffs; }
+    bool isNest()      const { return Flags & Nest; }
+    void setNest()     { Flags |= One << NestOffs; }
+
+    bool isReturned()  const { return Flags & Returned; }
+    void setReturned() { Flags |= One << ReturnedOffs; }
 
     unsigned getByValAlign() const {
       return (unsigned)
diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index e169bcf..1e7ccd8 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -1910,16 +1910,18 @@ public:
   struct ArgListEntry {
     SDValue Node;
     Type* Ty;
-    bool isSExt  : 1;
-    bool isZExt  : 1;
-    bool isInReg : 1;
-    bool isSRet  : 1;
-    bool isNest  : 1;
-    bool isByVal : 1;
+    bool isSExt     : 1;
+    bool isZExt     : 1;
+    bool isInReg    : 1;
+    bool isSRet     : 1;
+    bool isNest     : 1;
+    bool isByVal    : 1;
+    bool isReturned : 1;
     uint16_t Alignment;
 
     ArgListEntry() : isSExt(false), isZExt(false), isInReg(false),
-      isSRet(false), isNest(false), isByVal(false), Alignment(0) { }
+      isSRet(false), isNest(false), isByVal(false), isReturned(false),
+      Alignment(0) { }
   };
   typedef std::vector<ArgListEntry> ArgListTy;