From e4ffc030e2869bda17a9b9798092e929114863bd Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Sun, 22 Feb 2009 08:05:12 +0000
Subject: [PATCH] Be bug compatible with gcc by returning MMX values in RAX.

llvm-svn: 65274
---
 llvm/lib/Target/X86/X86CallingConv.td   |  5 +++--
 llvm/lib/Target/X86/X86ISelLowering.cpp | 15 ++++++++++-----
 llvm/test/CodeGen/X86/ret-mmx.ll        |  6 +++++-
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Target/X86/X86CallingConv.td b/llvm/lib/Target/X86/X86CallingConv.td
index 6742a90058a2..80bdbd0b1cfa 100644
--- a/llvm/lib/Target/X86/X86CallingConv.td
+++ b/llvm/lib/Target/X86/X86CallingConv.td
@@ -72,8 +72,9 @@ def RetCC_X86_64_C : CallingConv<[
   CCIfType<[f32], CCAssignToReg<[XMM0, XMM1]>>,
   CCIfType<[f64], CCAssignToReg<[XMM0, XMM1]>>,
 
-  // MMX vector types are always returned in XMM0.
-  CCIfType<[v8i8, v4i16, v2i32, v1i64, v2f32], CCAssignToReg<[XMM0, XMM1]>>,
+  // MMX vector types are always returned in RAX. This seems to disagree with
+  // ABI documentation but is bug compatible with gcc.
+  CCIfType<[v8i8, v4i16, v2i32, v1i64, v2f32], CCAssignToReg<[RAX]>>,
   CCDelegateTo<RetCC_X86Common>
 ]>;
 
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index efcb3f47ff77..674a633244d5 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -997,6 +997,14 @@ SDValue X86TargetLowering::LowerRET(SDValue Op, SelectionDAG &DAG) {
       continue;
     }
 
+    // 64-bit vector (MMX) values are returned in RAX.
+    if (Subtarget->is64Bit()) {
+      MVT ValVT = ValToCopy.getValueType();
+      if (VA.getLocReg() == X86::RAX &&
+          ValVT.isVector() && ValVT.getSizeInBits() == 64)
+        ValToCopy = DAG.getNode(ISD::BIT_CONVERT, dl, MVT::i64, ValToCopy);
+    }
+
     Chain = DAG.getCopyToReg(Chain, dl, VA.getLocReg(), ValToCopy, Flag);
     Flag = Chain.getValue(1);
   }
@@ -1073,13 +1081,10 @@ LowerCallResult(SDValue Chain, SDValue InFlag, CallSDNode *TheCall,
 
     SDValue Val;
     if (Is64Bit && CopyVT.isVector() && CopyVT.getSizeInBits() == 64) {
-      // For x86-64, MMX values are returned in XMM0 and XMM1. Issue an
-      // extract_vector_elt to i64 and then bit_convert it to the desired type.
+      // For x86-64, MMX values are returned in RAX.
       Chain = DAG.getCopyFromReg(Chain, dl, VA.getLocReg(),
-                                 MVT::v2i64, InFlag).getValue(1);
+                                 MVT::i64, InFlag).getValue(1);
       Val = Chain.getValue(0);
-      Val = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, MVT::i64,
-                        Val, DAG.getConstant(0, MVT::i64));
       Val = DAG.getNode(ISD::BIT_CONVERT, dl, CopyVT, Val);
     } else {
       Chain = DAG.getCopyFromReg(Chain, dl, VA.getLocReg(),
diff --git a/llvm/test/CodeGen/X86/ret-mmx.ll b/llvm/test/CodeGen/X86/ret-mmx.ll
index fe9380585de3..6587eabb7665 100644
--- a/llvm/test/CodeGen/X86/ret-mmx.ll
+++ b/llvm/test/CodeGen/X86/ret-mmx.ll
@@ -3,11 +3,15 @@
 
 @g_v1di = external global <1 x i64>
 
-define void @test_v1di() nounwind {
+define void @t1() nounwind {
 entry:
 	%call = call <1 x i64> @return_v1di()		; <<1 x i64>> [#uses=0]
 	store <1 x i64> %call, <1 x i64>* @g_v1di
         ret void
 }
 
+define <1 x i64> @t2() nounwind {
+	ret <1 x i64> <i64 1>
+}
+
 declare <1 x i64> @return_v1di()
-- 
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