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| 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 | 70d9929def5fda573a5c082620c0e7713decb94c (patch) | |
| tree | 88718e08840e7a6ba3a7d56a87ba662473bcb606 | |
| parent | 31a20d680ae23d9d1e368194c869074f8390fd95 (diff) | |
| download | bcm5719-llvm-70d9929def5fda573a5c082620c0e7713decb94c.tar.gz bcm5719-llvm-70d9929def5fda573a5c082620c0e7713decb94c.zip | |
Add comments explaining why there's only one register for
i8 return values.
llvm-svn: 67502
| -rw-r--r-- | llvm/lib/Target/X86/X86CallingConv.td | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/llvm/lib/Target/X86/X86CallingConv.td b/llvm/lib/Target/X86/X86CallingConv.td index d2fc86398e4..370bae7a50c 100644 --- a/llvm/lib/Target/X86/X86CallingConv.td +++ b/llvm/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]>>, |
