[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218451 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/CallingConvLower.h

@@ -35,6 +35,12 @@ public:
     SExt,      // The value is sign extended in the location.
     ZExt,      // The value is zero extended in the location.
     AExt,      // The value is extended with undefined upper bits.
+    SExtUpper, // The value is in the upper bits of the location and should be
+               // sign extended when retrieved.
+    ZExtUpper, // The value is in the upper bits of the location and should be
+               // zero extended when retrieved.
+    AExtUpper, // The value is in the upper bits of the location and should be
+               // extended with undefined upper bits when retrieved.
     BCvt,      // The value is bit-converted in the location.
     VExt,      // The value is vector-widened in the location.
                // FIXME: Not implemented yet. Code that uses AExt to mean
@@ -43,6 +49,7 @@ public:
     Indirect   // The location contains pointer to the value.
     // TODO: a subset of the value is in the location.
   };
+
 private:
   /// ValNo - This is the value number begin assigned (e.g. an argument number).
   unsigned ValNo;
@@ -146,6 +153,9 @@ public:
     return (HTP == AExt || HTP == SExt || HTP == ZExt);
   }
 
+  bool isUpperBitsInLoc() const {
+    return HTP == AExtUpper || HTP == SExtUpper || HTP == ZExtUpper;
+  }
 };
 
 /// CCAssignFn - This function assigns a location for Val, updating State to

include/llvm/Target/TargetCallingConv.td

@@ -119,6 +119,12 @@ class CCPromoteToType<ValueType destTy> : CCAction {
   ValueType DestTy = destTy;
 }
 
+/// CCPromoteToUpperBitsInType - If applied, this promotes the specified current
+/// value to the specified type and shifts the value into the upper bits.
+class CCPromoteToUpperBitsInType<ValueType destTy> : CCAction {
+  ValueType DestTy = destTy;
+}
+
 /// CCBitConvertToType - If applied, this bitconverts the specified current
 /// value to the specified type.
 class CCBitConvertToType<ValueType destTy> : CCAction {

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]>>,
 

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())
+    if (VA.isUpperBitsInLoc()) {
-      Val = DAG.getNode(ISD::BITCAST, DL, RVLocs[i].getValVT(), Val);
+      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;
 
-    if (RVLocs[i].getValVT() != RVLocs[i].getLocVT())
+    switch (VA.getLocInfo()) {
-      Val = DAG.getNode(ISD::BITCAST, DL, RVLocs[i].getLocVT(), Val);
+    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 (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);
 

test/CodeGen/Mips/cconv/return-struct.ll

@@ -0,0 +1,84 @@
+; RUN: llc -mtriple=mips-linux-gnu -relocation-model=static < %s | FileCheck --check-prefix=ALL --check-prefix=O32 --check-prefix=O32-BE %s
+; RUN: llc -mtriple=mipsel-linux-gnu -relocation-model=static < %s | FileCheck --check-prefix=ALL --check-prefix=O32 --check-prefix=O32-LE %s
+
+; RUN-TODO: llc -mtriple=mips64-linux-gnu -relocation-model=static -mattr=-n64,+o32 < %s | FileCheck --check-prefix=ALL --check-prefix=O32 %s
+; RUN-TODO: llc -mtriple=mips64el-linux-gnu -relocation-model=static -mattr=-n64,+o32 < %s | FileCheck --check-prefix=ALL --check-prefix=O32 %s
+
+; RUN: llc -mtriple=mips64-linux-gnu -relocation-model=static -mattr=-n64,+n32 < %s | FileCheck --check-prefix=ALL --check-prefix=N32 --check-prefix=N32-BE %s
+; RUN: llc -mtriple=mips64el-linux-gnu -relocation-model=static -mattr=-n64,+n32 < %s | FileCheck --check-prefix=ALL --check-prefix=N32 --check-prefix=N32-LE %s
+
+; RUN: llc -mtriple=mips64-linux-gnu -relocation-model=static -mattr=-n64,+n64 < %s | FileCheck --check-prefix=ALL --check-prefix=N64 --check-prefix=N64-BE %s
+; RUN: llc -mtriple=mips64el-linux-gnu -relocation-model=static -mattr=-n64,+n64 < %s | FileCheck --check-prefix=ALL --check-prefix=N64 --check-prefix=N64-LE %s
+
+; Test struct returns for all ABI's and byte orders.
+
+@struct_byte = global {i8} zeroinitializer
+@struct_2byte = global {i8,i8} zeroinitializer
+
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i32, i1)
+
+define inreg {i8} @ret_struct_i8() nounwind {
+entry:
+        %0 = load volatile {i8}* @struct_byte
+        ret {i8} %0
+}
+
+; ALL-LABEL: ret_struct_i8:
+; O32-DAG:           lui [[R1:\$[0-9]+]], %hi(struct_byte)
+; O32-DAG:           lbu $2, %lo(struct_byte)([[R1]])
+
+; N32-LE-DAG:        lui [[R1:\$[0-9]+]], %hi(struct_byte)
+; N32-LE-DAG:        lb $2, %lo(struct_byte)([[R1]])
+
+; N32-BE-DAG:        lui [[R1:\$[0-9]+]], %hi(struct_byte)
+; N32-BE-DAG:        lb [[R2:\$[0-9]+]], %lo(struct_byte)([[R1]])
+; N32-BE-DAG:        dsll $2, [[R2]], 56
+
+; N64-LE-DAG:        ld  [[R1:\$[0-9]+]], %got_disp(struct_byte)($1)
+; N64-LE-DAG:        lb $2, 0([[R1]])
+
+; N64-BE-DAG:        ld  [[R1:\$[0-9]+]], %got_disp(struct_byte)($1)
+; N64-BE-DAG:        lb [[R2:\$[0-9]+]], 0([[R1]])
+; N64-BE-DAG:        dsll $2, [[R2]], 56
+
+; This test is based on the way clang currently lowers {i8,i8} to {i16}.
+; FIXME: It should probably work for without any lowering too but this doesn't
+;        work as expected. Each member gets mapped to a register rather than
+;        packed into a single register.
+define inreg {i16} @ret_struct_i16() nounwind {
+entry:
+        %retval = alloca {i8,i8}, align 1
+        %0 = bitcast {i8,i8}* %retval to i8*
+        call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* getelementptr inbounds ({i8,i8}* @struct_2byte, i32 0, i32 0), i64 2, i32 1, i1 false)
+        %1 = bitcast {i8,i8}* %retval to {i16}*
+        %2 = load volatile {i16}* %1
+        ret {i16} %2
+}
+
+; ALL-LABEL: ret_struct_i16:
+; O32-DAG:           lui [[R1:\$[0-9]+]], %hi(struct_2byte)
+; O32-DAG:           lhu [[R2:\$[0-9]+]], %lo(struct_2byte)([[R1]])
+; O32-DAG:           sh  [[R2]], 0([[SP:\$sp]])
+; O32-DAG:           lhu $2, 0([[SP:\$sp]])
+
+; N32-LE-DAG:        lui [[R1:\$[0-9]+]], %hi(struct_2byte)
+; N32-LE-DAG:        lhu [[R2:\$[0-9]+]], %lo(struct_2byte)([[R1]])
+; N32-LE-DAG:        sh  [[R2]], 8([[SP:\$sp]])
+; N32-LE-DAG:        lh  $2, 8([[SP:\$sp]])
+
+; N32-BE-DAG:        lui [[R1:\$[0-9]+]], %hi(struct_2byte)
+; N32-BE-DAG:        lhu [[R2:\$[0-9]+]], %lo(struct_2byte)([[R1]])
+; N32-BE-DAG:        sh  [[R2]], 8([[SP:\$sp]])
+; N32-BE-DAG:        lh  [[R3:\$[0-9]+]], 8([[SP:\$sp]])
+; N32-BE-DAG:        dsll $2, [[R3]], 48
+
+; N64-LE-DAG:        ld  [[R1:\$[0-9]+]], %got_disp(struct_2byte)($1)
+; N64-LE-DAG:        lhu [[R2:\$[0-9]+]], 0([[R1]])
+; N64-LE-DAG:        sh  [[R2]], 8([[SP:\$sp]])
+; N64-LE-DAG:        lh  $2, 8([[SP:\$sp]])
+
+; N64-BE-DAG:        ld  [[R1:\$[0-9]+]], %got_disp(struct_2byte)($1)
+; N64-BE-DAG:        lhu [[R2:\$[0-9]+]], 0([[R1]])
+; N64-BE-DAG:        sh  [[R2]], 8([[SP:\$sp]])
+; N64-BE-DAG:        lh  [[R3:\$[0-9]+]], 8([[SP:\$sp]])
+; N64-BE-DAG:        dsll $2, [[R3]], 48

utils/TableGen/CallingConvEmitter.cpp

@@ -231,6 +231,21 @@ void CallingConvEmitter::EmitAction(Record *Action,
           << IndentStr << "else\n"
           << IndentStr << IndentStr << "LocInfo = CCValAssign::AExt;\n";
       }
+    } else if (Action->isSubClassOf("CCPromoteToUpperBitsInType")) {
+      Record *DestTy = Action->getValueAsDef("DestTy");
+      MVT::SimpleValueType DestVT = getValueType(DestTy);
+      O << IndentStr << "LocVT = " << getEnumName(DestVT) << ";\n";
+      if (MVT(DestVT).isFloatingPoint()) {
+        PrintFatalError("CCPromoteToUpperBitsInType does not handle floating "
+                        "point");
+      } else {
+        O << IndentStr << "if (ArgFlags.isSExt())\n"
+          << IndentStr << IndentStr << "LocInfo = CCValAssign::SExtUpper;\n"
+          << IndentStr << "else if (ArgFlags.isZExt())\n"
+          << IndentStr << IndentStr << "LocInfo = CCValAssign::ZExtUpper;\n"
+          << IndentStr << "else\n"
+          << IndentStr << IndentStr << "LocInfo = CCValAssign::AExtUpper;\n";
+      }
     } else if (Action->isSubClassOf("CCBitConvertToType")) {
       Record *DestTy = Action->getValueAsDef("DestTy");
       O << IndentStr << "LocVT = " << getEnumName(getValueType(DestTy)) <<";\n";