Correct VectorCall x86 (32 bit) behavior for SSE Register Assignment

[erichkeane]

Summary

In running some internal vectorcall tests in 32 bit mode, we discovered that the behavior I'd previously implemented for x64 (and applied to x32) regarding the assignment of SSE registers was incorrect. See spec here: https://msdn.microsoft.com/en-us/library/dn375768.aspx

My previous implementation applied register argument position from the x64 version to both. This isn't correct for x86, so this removes and refactors that section. Additionally, it corrects the integer/int-pointer assignments. Unlike x64, x86 permits integers to be assigned independent of position.

Finally, the code for 32 bit was cleaned up a little to clarify the intent, as well as given a descriptive comment.

[rnk]

Oh joy. :)

lgtm, thanks for debugging this. The difference makes sense after the fact when you think about Win x64's approach to va_arg and /homeparams, and how that isn't relevant for x86.

[erichkeane]

Thanks Reid!

lib/CodeGen/TargetInfo.cpp

class X86_32ABIInfo : public SwiftABIInfo {
   ABIArgInfo getIndirectReturnResult(QualType Ty, CCState &State) const;
 
   /// \brief Return the alignment to use for the given type on the stack.
   unsigned getTypeStackAlignInBytes(QualType Ty, unsigned Align) const;
 
   Class classify(QualType Ty) const;
   ABIArgInfo classifyReturnType(QualType RetTy, CCState &State) const;
   ABIArgInfo classifyArgumentType(QualType RetTy, CCState &State) const;
-  ABIArgInfo reclassifyHvaArgType(QualType RetTy, CCState &State, 
-                                  const ABIArgInfo& current) const;
+
   /// \brief Updates the number of available free registers, returns 
   /// true if any registers were allocated.
   bool updateFreeRegs(QualType Ty, CCState &State) const;
 
   bool shouldAggregateUseDirect(QualType Ty, CCState &State, bool &InReg,
                                 bool &NeedsPadding) const;
   bool shouldPrimitiveUseInReg(QualType Ty, CCState &State) const;
 
if (State.CC == llvm::CallingConv::X86_FastCall ||
 
     return (Ty->isIntegralOrEnumerationType() || Ty->isPointerType() || 
         Ty->isReferenceType());
   }
 
   return true;
 }
 
-ABIArgInfo
-X86_32ABIInfo::reclassifyHvaArgType(QualType Ty, CCState &State,
-                                    const ABIArgInfo &current) const {
-  // Assumes vectorCall calling convention.
-  const Type *Base = nullptr;
-  uint64_t NumElts = 0;
-
-  if (!Ty->isBuiltinType() && !Ty->isVectorType() &&
-      isHomogeneousAggregate(Ty, Base, NumElts)) {
-    if (State.FreeSSERegs >= NumElts) {
-      // HVA types get passed directly in registers if there is room.
-      State.FreeSSERegs -= NumElts;
-      return getDirectX86Hva();
-    }
-    // If there's no room, the HVA gets passed as normal indirect
-    // structure.
-    return getIndirectResult(Ty, /*ByVal=*/false, State);
-  } 
-  return current;
-}
-
 ABIArgInfo X86_32ABIInfo::classifyArgumentType(QualType Ty,
                                                CCState &State) const {
   // FIXME: Set alignment on indirect arguments.
 
   Ty = useFirstFieldIfTransparentUnion(Ty);
 
   // Check with the C++ ABI first.
   const RecordType *RT = Ty->getAs<RecordType>();
   if (RT) {
     CGCXXABI::RecordArgABI RAA = getRecordArgABI(RT, getCXXABI());
     if (RAA == CGCXXABI::RAA_Indirect) {
       return getIndirectResult(Ty, false, State);
     } else if (RAA == CGCXXABI::RAA_DirectInMemory) {
       // The field index doesn't matter, we'll fix it up later.
       return ABIArgInfo::getInAlloca(/*FieldIndex=*/0);
     }
   }
 
-  // vectorcall adds the concept of a homogenous vector aggregate, similar
-  // to other targets, regcall uses some of the HVA rules.
+  // Regcall uses the concept of a homogenous vector aggregate, similar
+  // to other targets.
   const Type *Base = nullptr;
   uint64_t NumElts = 0;
-  if ((State.CC == llvm::CallingConv::X86_VectorCall ||
-       State.CC == llvm::CallingConv::X86_RegCall) &&
+  if (State.CC == llvm::CallingConv::X86_RegCall &&
       isHomogeneousAggregate(Ty, Base, NumElts)) {
 
-    if (State.CC == llvm::CallingConv::X86_RegCall) {
-      if (State.FreeSSERegs >= NumElts) {
-        State.FreeSSERegs -= NumElts;
-        if (Ty->isBuiltinType() || Ty->isVectorType())
-          return ABIArgInfo::getDirect();
-        return ABIArgInfo::getExpand();
-
-      }
-      return getIndirectResult(Ty, /*ByVal=*/false, State);
-    } else if (State.CC == llvm::CallingConv::X86_VectorCall) {
-      if (State.FreeSSERegs >= NumElts && (Ty->isBuiltinType() || Ty->isVectorType())) {
-        // Actual floating-point types get registers first time through if
-        // there is registers available
-        State.FreeSSERegs -= NumElts;
-        return ABIArgInfo::getDirect();
-      }  else if (!Ty->isBuiltinType() && !Ty->isVectorType()) {
-        // HVA Types only get registers after everything else has been
-        // set, so it gets set as indirect for now.
-        return ABIArgInfo::getIndirect(getContext().getTypeAlignInChars(Ty));
-      }
-    }
   }
 
   if (isAggregateTypeForABI(Ty)) {
     // Structures with flexible arrays are always indirect.
     // FIXME: This should not be byval!
     if (RT && RT->getDecl()->hasFlexibleArrayMember())
       return getIndirectResult(Ty, true, State);
 
ABIArgInfo X86_32ABIInfo::classifyArgumentType(QualType Ty,
 
   if (InReg)
     return ABIArgInfo::getDirectInReg();
   return ABIArgInfo::getDirect();
 }
 
 void X86_32ABIInfo::computeVectorCallArgs(CGFunctionInfo &FI, CCState &State,
                                           bool &UsedInAlloca) const {
-  // Vectorcall only allows the first 6 parameters to be passed in registers,
-  // and homogeneous vector aggregates are only put into registers as a second
-  // priority.
-  unsigned Count = 0;
-  CCState ZeroState = State;
-  ZeroState.FreeRegs = ZeroState.FreeSSERegs = 0;
-  // HVAs must be done as a second priority for registers, so the deferred
-  // items are dealt with by going through the pattern a second time.
+  // Vectorcall x86 works subtly different than in x64, so the format is
+  // a bit different than the x64 version.  First, all vector types (not HVAs)
+  // are assigned, with the first 6 ending up in the YMM0-5 or XMM0-5 registers.
+  // This differs from the x64 implementation, where the first 6 by INDEX get
+  // registers.
+  // After that, integers AND HVAs are assigned Left to Right in the same pass.
+  // Integers are passed as ECX/EDX if one is available (in order).  HVAs will
+  // first take up the remaining YMM/XMM registers. If insufficient registers
+  // remain but an integer register (ECX/EDX) is available, it will be passed
+  // in that, else, on the stack.
   for (auto &I : FI.arguments()) {
-    if (Count < VectorcallMaxParamNumAsReg)
-      I.info = classifyArgumentType(I.type, State);
-    else
-      // Parameters after the 6th cannot be passed in registers,
-      // so pretend there are no registers left for them.
-      I.info = classifyArgumentType(I.type, ZeroState);
+    // First pass do all the vector types.
+    const Type *Base = nullptr;
+    uint64_t NumElts = 0;
+    const QualType& Ty = I.type;
+    if ((Ty->isVectorType() || Ty->isBuiltinType()) &&
+        isHomogeneousAggregate(Ty, Base, NumElts)) {
+      if (State.FreeSSERegs >= NumElts) {
+        State.FreeSSERegs -= NumElts;
+        I.info = ABIArgInfo::getDirect();
+      } else {
+        I.info = classifyArgumentType(Ty, State);
+      }
       UsedInAlloca |= (I.info.getKind() == ABIArgInfo::InAlloca);
-    ++Count;
     }
-  Count = 0;
-  // Go through the arguments a second time to get HVAs registers if there
-  // are still some available.
+  }
+
   for (auto &I : FI.arguments()) {
-    if (Count < VectorcallMaxParamNumAsReg)
-      I.info = reclassifyHvaArgType(I.type, State, I.info);
-    ++Count;
+    // Second pass, do the rest!
+    const Type *Base = nullptr;
+    uint64_t NumElts = 0;
+    const QualType& Ty = I.type;
+    bool IsHva = isHomogeneousAggregate(Ty, Base, NumElts);
+
+    if (IsHva && !Ty->isVectorType() && !Ty->isBuiltinType()) {
+      // Assign true HVAs (non vector/native FP types).
+      if (State.FreeSSERegs >= NumElts) {
+        State.FreeSSERegs -= NumElts;
+        I.info = getDirectX86Hva();
+      } else {
+        I.info = getIndirectResult(Ty, /*ByVal=*/false, State);
+      }
+    } else if (!IsHva) {
+      // Assign all Non-HVAs, so this will exclude Vector/FP args.
+      I.info = classifyArgumentType(Ty, State);
+      UsedInAlloca |= (I.info.getKind() == ABIArgInfo::InAlloca);
+    }
   }
 }
 
 void X86_32ABIInfo::computeInfo(CGFunctionInfo &FI) const {
   CCState State(FI.getCallingConvention());
   if (IsMCUABI)
     State.FreeRegs = 3;
   else if (State.CC == llvm::CallingConv::X86_FastCall)

 }
 
 void WinX86_64ABIInfo::computeVectorCallArgs(CGFunctionInfo &FI,
                                              unsigned FreeSSERegs,
                                              bool IsVectorCall,
                                              bool IsRegCall) const {
   unsigned Count = 0;
   for (auto &I : FI.arguments()) {
+    // Vectorcall in x64 only permits the first 6 arguments to be passed
+    // as XMM/YMM registers.
     if (Count < VectorcallMaxParamNumAsReg)
       I.info = classify(I.type, FreeSSERegs, false, IsVectorCall, IsRegCall);
     else {
       // Since these cannot be passed in registers, pretend no registers
       // are left.
       unsigned ZeroSSERegsAvail = 0;
       I.info = classify(I.type, /*FreeSSERegs=*/ZeroSSERegsAvail, false,
                         IsVectorCall, IsRegCall);
     }
     ++Count;
   }
 
-  Count = 0;
   for (auto &I : FI.arguments()) {
-    if (Count < VectorcallMaxParamNumAsReg)
-      I.info = reclassifyHvaArgType(I.type, FreeSSERegs, I.info);
-    ++Count;
   }
 }
 
 void WinX86_64ABIInfo::computeInfo(CGFunctionInfo &FI) const {
   bool IsVectorCall =
       FI.getCallingConvention() == llvm::CallingConv::X86_VectorCall;
   bool IsRegCall = FI.getCallingConvention() == llvm::CallingConv::X86_RegCall;
 

test/CodeGen/vectorcall.c

 
 typedef float __attribute__((ext_vector_type(3))) v3f32;
 struct OddSizeHVA { v3f32 x, y; };
 
 void __vectorcall odd_size_hva(struct OddSizeHVA a) {}
 // X32: define x86_vectorcallcc void @"\01odd_size_hva@@32"(%struct.OddSizeHVA inreg %a.coerce)
 // X64: define x86_vectorcallcc void @"\01odd_size_hva@@32"(%struct.OddSizeHVA inreg %a.coerce)
 
-// The Vectorcall ABI only allows passing the first 6 items in registers, so this shouldn't 
+// The Vectorcall ABI only allows passing the first 6 items in registers in x64, so this shouldn't
 // consider 'p7' as a register.  Instead p5 gets put into the register on the second pass.
-struct HFA2 __vectorcall AddParticles(struct HFA2 p1, float p2, struct HFA4 p3, int p4, struct HFA2 p5, float p6, float p7){ return p1;}
-// X32: define x86_vectorcallcc %struct.HFA2 @"\01AddParticles@@80"(%struct.HFA2 inreg %p1.coerce, float %p2, %struct.HFA4* inreg %p3, i32 inreg %p4, %struct.HFA2 inreg %p5.coerce, float %p6, float %p7)
-// X64: define x86_vectorcallcc %struct.HFA2 @"\01AddParticles@@96"(%struct.HFA2 inreg %p1.coerce, float %p2, %struct.HFA4* %p3, i32 %p4, %struct.HFA2 inreg %p5.coerce, float %p6, float %p7)
+// x86 should pass p2, p6 and p7 in registers, then p1 in the second pass.
+struct HFA2 __vectorcall AddParticles(struct HFA2 p1, float p2, struct HFA4 p3, int p4, struct HFA2 p5, float p6, float p7, int p8){ return p1;}
+// X32: define x86_vectorcallcc %struct.HFA2 @"\01AddParticles@@84"(%struct.HFA2 inreg %p1.coerce, float %p2, %struct.HFA4* inreg %p3, i32 inreg %p4, %struct.HFA2* %p5, float %p6, float %p7, i32 %p8)
+// X64: define x86_vectorcallcc %struct.HFA2 @"\01AddParticles@@104"(%struct.HFA2 inreg %p1.coerce, float %p2, %struct.HFA4* %p3, i32 %p4, %struct.HFA2 inreg %p5.coerce, float %p6, float %p7, i32 %p8)
+
+// Vectorcall in both architectures allows passing of an HVA as long as there is room,
+// even if it is not one of the first 6 arguments.  First pass puts p4 into a
+// register on both.  p9 ends up in a register in x86 only.  Second pass puts p1
+// in a register, does NOT put p7 in a register (since theres no room), then puts 
+// p8 in a register.
+void __vectorcall HVAAnywhere(struct HFA2 p1, int p2, int p3, float p4, int p5, int p6, struct HFA4 p7, struct HFA2 p8, float p9){}
+// X32: define x86_vectorcallcc void @"\01HVAAnywhere@@88"(%struct.HFA2 inreg %p1.coerce, i32 inreg %p2, i32 inreg %p3, float %p4, i32 %p5, i32 %p6, %struct.HFA4* %p7, %struct.HFA2 inreg %p8.coerce, float %p9)
+// X64: define x86_vectorcallcc void @"\01HVAAnywhere@@112"(%struct.HFA2 inreg %p1.coerce, i32 %p2, i32 %p3, float %p4, i32 %p5, i32 %p6, %struct.HFA4* %p7, %struct.HFA2 inreg %p8.coerce, float %p9) 
+