Swift Calling Convention: use %RAX for sret.

We don't need to copy the sret argument into %rax upon return.
rdar://25671494

llvm-svn: 267579

3 files changed, 16 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86CallingConv.td b/llvm/lib/Target/X86/X86CallingConv.td
index ed17b1d4d04..263a207a667 100644
--- a/llvm/lib/Target/X86/X86CallingConv.td
+++ b/llvm/lib/Target/X86/X86CallingConv.td
@@ -303,6 +303,10 @@ def CC_X86_64_C : CallingConv<[
   // A SwiftError is passed in R12.
   CCIfSwiftError<CCIfType<[i64], CCAssignToReg<[R12]>>>,
 
+  // For Swift Calling Convention, pass sret in %RAX.
+  CCIfCC<"CallingConv::Swift",
+    CCIfSRet<CCIfType<[i64], CCAssignToReg<[RAX]>>>>,
+
   // The first 6 integer arguments are passed in integer registers.
   CCIfType<[i32], CCAssignToReg<[EDI, ESI, EDX, ECX, R8D, R9D]>>,
   CCIfType<[i64], CCAssignToReg<[RDI, RSI, RDX, RCX, R8 , R9 ]>>,
diff --git a/llvm/lib/Target/X86/X86FastISel.cpp b/llvm/lib/Target/X86/X86FastISel.cpp
index 697bd8aace7..6614ac0dd4a 100644
--- a/llvm/lib/Target/X86/X86FastISel.cpp
+++ b/llvm/lib/Target/X86/X86FastISel.cpp
@@ -1121,11 +1121,14 @@ bool X86FastISel::X86SelectRet(const Instruction *I) {
     RetRegs.push_back(VA.getLocReg());
   }
 
+  // Swift calling convention does not require we copy the sret argument
+  // into %rax/%eax for the return, and SRetReturnReg is not set for Swift.
+
   // All x86 ABIs require that for returning structs by value we copy
   // the sret argument into %rax/%eax (depending on ABI) for the return.
   // We saved the argument into a virtual register in the entry block,
   // so now we copy the value out and into %rax/%eax.
-  if (F.hasStructRetAttr()) {
+  if (F.hasStructRetAttr() && CC != CallingConv::Swift) {
     unsigned Reg = X86MFInfo->getSRetReturnReg();
     assert(Reg &&
            "SRetReturnReg should have been set in LowerFormalArguments()!");
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 4d9d4616e69..ad844601c24 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -2082,6 +2082,9 @@ X86TargetLowering::LowerReturn(SDValue Chain,
     RetOps.push_back(DAG.getRegister(VA.getLocReg(), VA.getLocVT()));
   }
 
+  // Swift calling convention does not require we copy the sret argument
+  // into %rax/%eax for the return, and SRetReturnReg is not set for Swift.
+
   // All x86 ABIs require that for returning structs by value we copy
   // the sret argument into %rax/%eax (depending on ABI) for the return.
   // We saved the argument into a virtual register in the entry block,
@@ -2610,6 +2613,11 @@ SDValue X86TargetLowering::LowerFormalArguments(
   }
 
   for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
+    // Swift calling convention does not require we copy the sret argument
+    // into %rax/%eax for the return. We don't set SRetReturnReg for Swift.
+    if (CallConv == CallingConv::Swift)
+      continue;
+
     // All x86 ABIs require that for returning structs by value we copy the
     // sret argument into %rax/%eax (depending on ABI) for the return. Save
     // the argument into a virtual register so that we can access it from the