diff options
| -rw-r--r-- | lib/Target/X86/X86CallingConv.td | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/lib/Target/X86/X86CallingConv.td b/lib/Target/X86/X86CallingConv.td index 6924520ab8..7f99203a83 100644 --- a/lib/Target/X86/X86CallingConv.td +++ b/lib/Target/X86/X86CallingConv.td @@ -22,13 +22,14 @@ class CCIfSubtarget<string F, CCAction A> // Return-value conventions common to all X86 CC's. def RetCC_X86Common : CallingConv<[ - // Scalar values are returned in AX first, then DX, except for i8 where - // the convention is to return values in AL and AH. However, using AL and - // AH is problematic -- a return of {i16,i8} would end up using AX and AH, - // and one value would clobber the other. C front-ends are currently expected - // to pack two i8 values into an i16 in the rare situations where this - // is necessary. - CCIfType<[i8] , CCAssignToReg<[AL]>>, + // Scalar values are returned in AX first, then DX. For i8, the ABI + // requires the values to be in AL and AH, however this code uses AL and DL + // instead. This is because using AH for the second register conflicts with + // the way LLVM does multiple return values -- a return of {i16,i8} would end + // up in AX and AH, which overlap. Front-ends wishing to conform to the ABI + // for functions that return two i8 values are currently expected to pack the + // values into an i16 (which uses AX, and thus AL:AH). + CCIfType<[i8] , CCAssignToReg<[AL, DL]>>, CCIfType<[i16], CCAssignToReg<[AX, DX]>>, CCIfType<[i32], CCAssignToReg<[EAX, EDX]>>, CCIfType<[i64], CCAssignToReg<[RAX, RDX]>>, |