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[X86] Add a FIXME about why the CWD/CDQ/CQO have a bogus implicit def of the A register. NFC 

The instructions copy the sign bit of the A register to every bit
of the D register. But they don't write to the A register.

llvm-svn: 371094
This commit is contained in:
Craig Topper 2019-09-05 17:24:34 +00:00
parent 673da001c5
commit 97aa42f5df
1 changed files with 5 additions and 6 deletions
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11
llvm/lib/Target/X86/X86InstrExtension.td
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@ -17,19 +17,18 @@ let hasSideEffects = 0 in {
let Defs = [EAX], Uses = [AX] in // EAX = signext(AX) let Defs = [EAX], Uses = [AX] in // EAX = signext(AX)
def CWDE : I<0x98, RawFrm, (outs), (ins), def CWDE : I<0x98, RawFrm, (outs), (ins),
"{cwtl|cwde}", []>, OpSize32, Sched<[WriteALU]>; "{cwtl|cwde}", []>, OpSize32, Sched<[WriteALU]>;
let Defs = [RAX], Uses = [EAX] in // RAX = signext(EAX)
def CDQE : RI<0x98, RawFrm, (outs), (ins),
"{cltq|cdqe}", []>, Sched<[WriteALU]>, Requires<[In64BitMode]>;
// FIXME: CWD/CDQ/CQO shouldn't Def the A register, but the fast register
// allocator crashes if you remove it.
let Defs = [AX,DX], Uses = [AX] in // DX:AX = signext(AX) let Defs = [AX,DX], Uses = [AX] in // DX:AX = signext(AX)
def CWD : I<0x99, RawFrm, (outs), (ins), def CWD : I<0x99, RawFrm, (outs), (ins),
"{cwtd|cwd}", []>, OpSize16, Sched<[WriteALU]>; "{cwtd|cwd}", []>, OpSize16, Sched<[WriteALU]>;
let Defs = [EAX,EDX], Uses = [EAX] in // EDX:EAX = signext(EAX) let Defs = [EAX,EDX], Uses = [EAX] in // EDX:EAX = signext(EAX)
def CDQ : I<0x99, RawFrm, (outs), (ins), def CDQ : I<0x99, RawFrm, (outs), (ins),
"{cltd|cdq}", []>, OpSize32, Sched<[WriteALU]>; "{cltd|cdq}", []>, OpSize32, Sched<[WriteALU]>;
let Defs = [RAX], Uses = [EAX] in // RAX = signext(EAX)
def CDQE : RI<0x98, RawFrm, (outs), (ins),
"{cltq|cdqe}", []>, Sched<[WriteALU]>, Requires<[In64BitMode]>;
let Defs = [RAX,RDX], Uses = [RAX] in // RDX:RAX = signext(RAX) let Defs = [RAX,RDX], Uses = [RAX] in // RDX:RAX = signext(RAX)
def CQO : RI<0x99, RawFrm, (outs), (ins), def CQO : RI<0x99, RawFrm, (outs), (ins),
"{cqto|cqo}", []>, Sched<[WriteALU]>, Requires<[In64BitMode]>; "{cqto|cqo}", []>, Sched<[WriteALU]>, Requires<[In64BitMode]>;