diff options
| author | Dan Gohman <gohman@apple.com> | 2009-03-23 04:28:24 +0000 |
|---|---|---|
| committer | Dan Gohman <gohman@apple.com> | 2009-03-23 04:28:24 +0000 |
| commit | 82f84159e0ec945657054ddcf465aca3253339ab (patch) | |
| tree | c99519efec0ecb935823f8dbed53343a2b1e44f9 /lib/Target/X86/X86CallingConv.td | |
| parent | a38ff646bc0ca873b3fe73b8d69e31209bedb2e2 (diff) | |
| download | llvm-82f84159e0ec945657054ddcf465aca3253339ab.tar.gz llvm-82f84159e0ec945657054ddcf465aca3253339ab.tar.bz2 llvm-82f84159e0ec945657054ddcf465aca3253339ab.tar.xz | |
Add comments explaining why there's only one register for
i8 return values.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67502 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/X86/X86CallingConv.td')
| -rw-r--r-- | lib/Target/X86/X86CallingConv.td | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/lib/Target/X86/X86CallingConv.td b/lib/Target/X86/X86CallingConv.td index d2fc86398e..370bae7a50 100644 --- a/lib/Target/X86/X86CallingConv.td +++ b/lib/Target/X86/X86CallingConv.td @@ -22,7 +22,12 @@ 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. + // 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 + // is AH 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]>>, CCIfType<[i16], CCAssignToReg<[AX, DX]>>, CCIfType<[i32], CCAssignToReg<[EAX, EDX]>>, |