[mips] Add CCValAssign::[ASZ]ExtUpper and CCPromoteToUpperBitsInType and handle struct's correctly on big-endian N32/N64 return values.

Summary:
The N32/N64 ABI's require that structs passed in registers are laid out
such that spilling the register with 'sd' places the struct at the lowest
address. For little endian this is trivial but for big-endian it requires
that structs are shifted into the upper bits of the register.

We also require that structs passed in registers have the 'inreg'
attribute for big-endian N32/N64 to work correctly. This is because the
tablegen-erated calling convention implementation only has access to the
lowered form of struct arguments (one or more integers of up to 64-bits
each) and is unable to determine the original type.

Reviewers: vmedic

Reviewed By: vmedic

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5286

llvm-svn: 218451

2 files changed, 82 insertions, 4 deletions

diff --git a/llvm/lib/Target/Mips/MipsCallingConv.td b/llvm/lib/Target/Mips/MipsCallingConv.td
index 1f3b89be656..013fb0de3e3 100644
--- a/llvm/lib/Target/Mips/MipsCallingConv.td
+++ b/llvm/lib/Target/Mips/MipsCallingConv.td
@@ -92,6 +92,14 @@ def CC_MipsN_VarArg : CallingConv<[
 ]>;
 
 def RetCC_MipsN : CallingConv<[
+  // Aggregate returns are positioned at the lowest address in the slot for
+  // both little and big-endian targets. When passing in registers, this
+  // requires that big-endian targets shift the value into the upper bits.
+  CCIfSubtarget<"isLittle()",
+      CCIfType<[i8, i16, i32], CCIfInReg<CCPromoteToType<i64>>>>,
+  CCIfSubtargetNot<"isLittle()",
+      CCIfType<[i8, i16, i32], CCIfInReg<CCPromoteToUpperBitsInType<i64>>>>,
+
   // i32 are returned in registers V0, V1
   CCIfType<[i32], CCAssignToReg<[V0, V1]>>,
 
diff --git a/llvm/lib/Target/Mips/MipsISelLowering.cpp b/llvm/lib/Target/Mips/MipsISelLowering.cpp
index 0dfc5d743d8..df73b6d3fb7 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsISelLowering.cpp
@@ -2696,13 +2696,49 @@ MipsTargetLowering::LowerCallResult(SDValue Chain, SDValue InFlag,
 
   // Copy all of the result registers out of their specified physreg.
   for (unsigned i = 0; i != RVLocs.size(); ++i) {
+    CCValAssign &VA = RVLocs[i];
+    assert(VA.isRegLoc() && "Can only return in registers!");
+
     SDValue Val = DAG.getCopyFromReg(Chain, DL, RVLocs[i].getLocReg(),
                                      RVLocs[i].getLocVT(), InFlag);
     Chain = Val.getValue(1);
     InFlag = Val.getValue(2);
 
-    if (RVLocs[i].getValVT() != RVLocs[i].getLocVT())
-      Val = DAG.getNode(ISD::BITCAST, DL, RVLocs[i].getValVT(), Val);
+    if (VA.isUpperBitsInLoc()) {
+      unsigned ValSizeInBits = Ins[i].ArgVT.getSizeInBits();
+      unsigned LocSizeInBits = VA.getLocVT().getSizeInBits();
+      unsigned Shift =
+          VA.getLocInfo() == CCValAssign::ZExtUpper ? ISD::SRL : ISD::SRA;
+      Val = DAG.getNode(
+          Shift, DL, VA.getLocVT(), Val,
+          DAG.getConstant(LocSizeInBits - ValSizeInBits, VA.getLocVT()));
+    }
+
+    switch (VA.getLocInfo()) {
+    default:
+      llvm_unreachable("Unknown loc info!");
+    case CCValAssign::Full:
+      break;
+    case CCValAssign::BCvt:
+      Val = DAG.getNode(ISD::BITCAST, DL, VA.getValVT(), Val);
+      break;
+    case CCValAssign::AExt:
+    case CCValAssign::AExtUpper:
+      Val = DAG.getNode(ISD::TRUNCATE, DL, VA.getValVT(), Val);
+      break;
+    case CCValAssign::ZExt:
+    case CCValAssign::ZExtUpper:
+      Val = DAG.getNode(ISD::AssertZext, DL, VA.getLocVT(), Val,
+                        DAG.getValueType(VA.getValVT()));
+      Val = DAG.getNode(ISD::TRUNCATE, DL, VA.getValVT(), Val);
+      break;
+    case CCValAssign::SExt:
+    case CCValAssign::SExtUpper:
+      Val = DAG.getNode(ISD::AssertSext, DL, VA.getLocVT(), Val,
+                        DAG.getValueType(VA.getValVT()));
+      Val = DAG.getNode(ISD::TRUNCATE, DL, VA.getValVT(), Val);
+      break;
+    }
 
     InVals.push_back(Val);
   }
@@ -2902,9 +2938,43 @@ MipsTargetLowering::LowerReturn(SDValue Chain,
     SDValue Val = OutVals[i];
     CCValAssign &VA = RVLocs[i];
     assert(VA.isRegLoc() && "Can only return in registers!");
+    bool UseUpperBits = false;
+
+    switch (VA.getLocInfo()) {
+    default:
+      llvm_unreachable("Unknown loc info!");
+    case CCValAssign::Full:
+      break;
+    case CCValAssign::BCvt:
+      Val = DAG.getNode(ISD::BITCAST, DL, VA.getLocVT(), Val);
+      break;
+    case CCValAssign::AExtUpper:
+      UseUpperBits = true;
+      // Fallthrough
+    case CCValAssign::AExt:
+      Val = DAG.getNode(ISD::ANY_EXTEND, DL, VA.getLocVT(), Val);
+      break;
+    case CCValAssign::ZExtUpper:
+      UseUpperBits = true;
+      // Fallthrough
+    case CCValAssign::ZExt:
+      Val = DAG.getNode(ISD::ZERO_EXTEND, DL, VA.getLocVT(), Val);
+      break;
+    case CCValAssign::SExtUpper:
+      UseUpperBits = true;
+      // Fallthrough
+    case CCValAssign::SExt:
+      Val = DAG.getNode(ISD::SIGN_EXTEND, DL, VA.getLocVT(), Val);
+      break;
+    }
 
-    if (RVLocs[i].getValVT() != RVLocs[i].getLocVT())
-      Val = DAG.getNode(ISD::BITCAST, DL, RVLocs[i].getLocVT(), Val);
+    if (UseUpperBits) {
+      unsigned ValSizeInBits = Outs[i].ArgVT.getSizeInBits();
+      unsigned LocSizeInBits = VA.getLocVT().getSizeInBits();
+      Val = DAG.getNode(
+          ISD::SHL, DL, VA.getLocVT(), Val,
+          DAG.getConstant(LocSizeInBits - ValSizeInBits, VA.getLocVT()));
+    }
 
     Chain = DAG.getCopyToReg(Chain, DL, VA.getLocReg(), Val, Flag);