Complete formal arguments for the SPARC v9 64-bit ABI.

All arguments are formally assigned to stack positions and then promoted
to floating point and integer registers. Since there are more floating
point registers than integer registers, this can cause situations where
floating point arguments are assigned to registers after integer
arguments that where assigned to the stack.

Use the inreg flag to indicate 32-bit fragments of structs containing
both float and int members.

The three-way shadowing between stack, integer, and floating point
registers requires custom argument lowering. The good news is that
return values are passed in the exact same way, and we can share the
code.

Still missing:

 - Update LowerReturn to handle structs returned in registers.
 - LowerCall.
 - Variadic functions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178958 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 86 insertions, 23 deletions

diff --git a/lib/Target/Sparc/SparcCallingConv.td b/lib/Target/Sparc/SparcCallingConv.td
index b38ac616dc..54784e0188 100644
--- a/lib/Target/Sparc/SparcCallingConv.td
+++ b/lib/Target/Sparc/SparcCallingConv.td
@@ -12,25 +12,9 @@
 //===----------------------------------------------------------------------===//
 
 //===----------------------------------------------------------------------===//
-// Return Value Calling Conventions
+// SPARC v8 32-bit.
 //===----------------------------------------------------------------------===//
 
-// Sparc 32-bit C return-value convention.
-def RetCC_Sparc32 : CallingConv<[
-  CCIfType<[i32], CCAssignToReg<[I0, I1, I2, I3, I4, I5]>>,
-  CCIfType<[f32], CCAssignToReg<[F0, F1, F2, F3]>>,
-  CCIfType<[f64], CCAssignToReg<[D0, D1]>>
-]>;
-
-// Sparc 64-bit C return-value convention.
-def RetCC_Sparc64 : CallingConv<[
-  CCIfType<[i32], CCPromoteToType<i64>>,
-  CCIfType<[i64], CCAssignToReg<[I0, I1, I2, I3, I4, I5]>>,
-  CCIfType<[f32], CCAssignToReg<[F0, F1, F2, F3]>>,
-  CCIfType<[f64], CCAssignToReg<[D0, D1]>>
-]>;
-
-// Sparc 32-bit C Calling convention.
 def CC_Sparc32 : CallingConv<[
   //Custom assign SRet to [sp+64].
   CCIfSRet<CCCustom<"CC_Sparc_Assign_SRet">>,
@@ -43,14 +27,93 @@ def CC_Sparc32 : CallingConv<[
   CCAssignToStack<4, 4>
 ]>;
 
-// Sparc 64-bit C Calling convention.
+def RetCC_Sparc32 : CallingConv<[
+  CCIfType<[i32], CCAssignToReg<[I0, I1, I2, I3, I4, I5]>>,
+  CCIfType<[f32], CCAssignToReg<[F0, F1, F2, F3]>>,
+  CCIfType<[f64], CCAssignToReg<[D0, D1]>>
+]>;
+
+
+//===----------------------------------------------------------------------===//
+// SPARC v9 64-bit.
+//===----------------------------------------------------------------------===//
+//
+// The 64-bit ABI conceptually assigns all function arguments to a parameter
+// array starting at [%fp+BIAS+128] in the callee's stack frame. All arguments
+// occupy a multiple of 8 bytes in the array. Integer arguments are extended to
+// 64 bits by the caller. Floats are right-aligned in their 8-byte slot, the
+// first 4 bytes in the slot are undefined.
+//
+// The integer registers %i0 to %i5 shadow the first 48 bytes of the parameter
+// array at fixed offsets. Integer arguments are promoted to registers when
+// possible.
+//
+// The floating point registers %f0 to %f31 shadow the first 128 bytes of the
+// parameter array at fixed offsets. Float and double parameters are promoted
+// to these registers when possible.
+//
+// Structs up to 16 bytes in size are passed by value. They are right-aligned
+// in one or two 8-byte slots in the parameter array. Struct members are
+// promoted to both floating point and integer registers when possible. A
+// struct containing two floats would thus be passed in %f0 and %f1, while two
+// float function arguments would occupy 8 bytes each, and be passed in %f1 and
+// %f3.
+//
+// When a struct { int, float } is passed by value, the int goes in the high
+// bits of an integer register while the float goes in a floating point
+// register.
+//
+// The difference is encoded in LLVM IR using the inreg atttribute on function
+// arguments:
+//
+//   C:   void f(float, float);
+//   IR:  declare void f(float %f1, float %f3)
+//
+//   C:   void f(struct { float f0, f1; });
+//   IR:  declare void f(float inreg %f0, float inreg %f1)
+//
+//   C:   void f(int, float);
+//   IR:  declare void f(int signext %i0, float %f3)
+//
+//   C:   void f(struct { int i0high; float f1; });
+//   IR:  declare void f(i32 inreg %i0high, float inreg %f1)
+//
+// Two ints in a struct are simply coerced to i64:
+//
+//   C:   void f(struct { int i0high, i0low; });
+//   IR:  declare void f(i64 %i0.coerced)
+//
+// The frontend and backend divide the task of producing ABI compliant code for
+// C functions. The C frontend will:
+//
+//  - Annotate integer arguments with zeroext or signext attributes.
+//
+//  - Split structs into one or two 64-bit sized chunks, or 32-bit chunks with
+//    inreg attributes.
+//
+//  - Pass structs larger than 16 bytes indirectly with an explicit pointer
+//    argument. The byval attribute is not used.
+//
+// The backend will:
+//
+//  - Assign all arguments to 64-bit aligned stack slots, 32-bits for inreg.
+//
+//  - Promote to integer or floating point registers depending on type.
+//
+// Function return values are passed exactly like function arguments, except a
+// struct up to 32 bytes in size can be returned in registers.
+
+// Function arguments AND return values.
 def CC_Sparc64 : CallingConv<[
+  // The frontend uses the inreg flag to indicate i32 and float arguments from
+  // structs. These arguments are not promoted to 64 bits, but they can still
+  // be assigned to integer and float registers.
+  CCIfInReg<CCIfType<[i32, f32], CCCustom<"CC_Sparc64_Half">>>,
+
   // All integers are promoted to i64 by the caller.
   CCIfType<[i32], CCPromoteToType<i64>>,
-  // Integer arguments get passed in integer registers if there is space.
-  CCIfType<[i64], CCAssignToReg<[I0, I1, I2, I3, I4, I5]>>,
-  // FIXME: Floating point arguments.
 
-  // Alternatively, they are assigned to the stack in 8-byte aligned units.
-  CCAssignToStack<8, 8>
+  // Custom assignment is required because stack space is reserved for all
+  // arguments whether they are passed in registers or not.
+  CCCustom<"CC_Sparc64_Full">
 ]>;