[AArch64] Fix va_arg for soft-float

The AArch64 back-end already avoids saving the FP registers to the
va_list when the FP registers aren't present, but clang also needs to
know not to load them from the FP register save area when generating
code for va_arg.

The layout of va_list remains the same, but the vr_top and vr_offs
fields are unused.

Change-Id: I5d3dee1ac4a29f189432957910662939b79d9329

Author: ostannard

clang/lib/CodeGen/Targets/AArch64.cpp

@@ -53,8 +53,8 @@ class AArch64ABIInfo : public ABIInfo {
   Address EmitDarwinVAArg(Address VAListAddr, QualType Ty,
                           CodeGenFunction &CGF) const;
 
-  Address EmitAAPCSVAArg(Address VAListAddr, QualType Ty,
-                         CodeGenFunction &CGF) const;
+  Address EmitAAPCSVAArg(Address VAListAddr, QualType Ty, CodeGenFunction &CGF,
+                         AArch64ABIKind Kind) const;
 
   Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                     QualType Ty) const override {
@@ -65,7 +65,7 @@ class AArch64ABIInfo : public ABIInfo {
 
     return Kind == AArch64ABIKind::Win64 ? EmitMSVAArg(CGF, VAListAddr, Ty)
            : isDarwinPCS()               ? EmitDarwinVAArg(VAListAddr, Ty, CGF)
-                                         : EmitAAPCSVAArg(VAListAddr, Ty, CGF);
+                                         : EmitAAPCSVAArg(VAListAddr, Ty, CGF, Kind);
   }
 
   Address EmitMSVAArg(CodeGenFunction &CGF, Address VAListAddr,
@@ -516,7 +516,8 @@ bool AArch64ABIInfo::isZeroLengthBitfieldPermittedInHomogeneousAggregate()
 }
 
 Address AArch64ABIInfo::EmitAAPCSVAArg(Address VAListAddr, QualType Ty,
-                                       CodeGenFunction &CGF) const {
+                                       CodeGenFunction &CGF,
+                                       AArch64ABIKind Kind) const {
   ABIArgInfo AI = classifyArgumentType(Ty, /*IsVariadic=*/true,
                                        CGF.CurFnInfo->getCallingConvention());
   // Empty records are ignored for parameter passing purposes.
@@ -541,7 +542,8 @@ Address AArch64ABIInfo::EmitAAPCSVAArg(Address VAListAddr, QualType Ty,
     BaseTy = ArrTy->getElementType();
     NumRegs = ArrTy->getNumElements();
   }
-  bool IsFPR = BaseTy->isFloatingPointTy() || BaseTy->isVectorTy();
+  bool IsFPR = Kind == AArch64ABIKind::AAPCS &&
+               (BaseTy->isFloatingPointTy() || BaseTy->isVectorTy());
 
   // The AArch64 va_list type and handling is specified in the Procedure Call
   // Standard, section B.4:

clang/test/CodeGen/aarch64-soft-float-abi.c

@@ -1,6 +1,9 @@
 // RUN: %clang_cc1 -triple aarch64 -target-feature +fp-armv8 -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,HARD
 // RUN: %clang_cc1 -triple aarch64 -target-feature -fp-armv8 -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,SOFT
 
+// The va_list type does not change between the ABIs
+// CHECK: %struct.__va_list = type { ptr, ptr, ptr, i32, i32 }
+
 // Floats are passed in integer registers, this will be handled by the backend.
 // CHECK: define dso_local half @test0(half noundef %a)
 // CHECK: define dso_local bfloat @test1(bfloat noundef %a)
@@ -30,6 +33,21 @@ struct B {
 // HARD: define dso_local %struct.B @test11([2 x double] alignstack(8) %a.coerce)
 struct B test11(struct B a) { return a; }
 
+#include <stdarg.h>
+
+// For variadic arguments, va_arg will always retreive 
+// CHECK-LABEL: define dso_local double @test20(i32 noundef %a, ...)
+// CHECK: %vl = alloca %struct.__va_list, align 8
+// SOFT: %gr_offs_p = getelementptr inbounds %struct.__va_list, ptr %vl, i32 0, i32 3
+// SOFT: %reg_top_p = getelementptr inbounds %struct.__va_list, ptr %vl, i32 0, i32 1
+// HARD: %vr_offs_p = getelementptr inbounds %struct.__va_list, ptr %vl, i32 0, i32 4
+// HARD: %reg_top_p = getelementptr inbounds %struct.__va_list, ptr %vl, i32 0, i32 2
+double test20(int a, ...) {
+  va_list vl;
+  va_start(vl, a);
+  return va_arg(vl, double);
+}
+
 // Vector types are only available for targets with the correct hardware, and
 // their calling-convention is left undefined by the soft-float ABI, so they
 // aren't tested here.