[LLVMdev] Codegen/Register allocation question.

[Lang Hames]

Hi LLVMers,

I have finally sorted out licensing issues and found some time, so I'm
trying to port my PBQP register allocator to 2.4 in order to
contribute it (if you want it). I've run into a bug that has me
confused though.

I'm currently failing the following assertion:

llc: VirtRegMap.cpp:1733:
void<unnamed>::LocalSpiller::RewriteMBB(llvm::MachineBasicBlock&,
llvm::VirtRegMap&): Assertion `KillRegs[0] == Dst' failed.

when attempting to allocate this machine function:

entry:
4       %reg1024<def,dead> = MOV32rr %EDI<kill>
12      %reg1025<def,dead> = MOV64rr %RSI<kill>
20      ADJCALLSTACKDOWN 0, %ESP<imp-def>, %EFLAGS<imp-def,dead>, %ESP<imp-use>
28      %reg1026<def> = MOV8ri 4
36      %reg1027<def> = FsFLD0SD
44      %reg1028<def> = LEA64r %reg0, 1, %reg0, <ga:.str1>
52      %RDI<def> = MOV64rr %reg1028<kill>
60      %XMM0<def> = FsMOVAPDrr %reg1027
68      %XMM1<def> = FsMOVAPDrr %reg1027
76      %XMM2<def> = FsMOVAPDrr %reg1027
84      %XMM3<def> = FsMOVAPDrr %reg1027<kill>
92      %AL<def> = MOV8rr %reg1026<kill>
100     CALL64pcrel32 <ga:printf>, %RDI<kill>, %XMM0<kill>,
%XMM1<kill>, %XMM2<kill>, %XMM3<kill>, %AL<kill>, %RAX<imp-def>,
%RCX<imp-def,dead>, %RDX<imp-def,dead>, %RSI<imp-def,dead>,
%RDI<imp-def,dead>, %R8<imp-def,dead>, %R9<imp-def,dead>,
%R10<imp-def,dead>, %R11<imp-def,dead>, %FP0<imp-def,dead>,
%FP1<imp-def,dead>, %FP2<imp-def,dead>, %FP3<imp-def,dead>,
%FP4<imp-def,dead>, %FP5<imp-def,dead>, %FP6<imp-def,dead>,
%ST0<imp-def,dead>, %ST1<imp-def,dead>, %MM0<imp-def,dead>,
%MM1<imp-def,dead>, %MM2<imp-def,dead>, %MM3<imp-def,dead>,
%MM4<imp-def,dead>, %MM5<imp-def,dead>, %MM6<imp-def,dead>,
%MM7<imp-def,dead>, %XMM0<imp-def,dead>, %XMM1<imp-def,dead>,
%XMM2<imp-def,dead>, %XMM3<imp-def,dead>, %XMM4<imp-def,dead>,
%XMM5<imp-def,dead>, %XMM6<imp-def,dead>, %XMM7<imp-def,dead>,
%XMM8<imp-def,dead>, %XMM9<imp-def,dead>, %XMM10<imp-def,dead>,
%XMM11<imp-def,dead>, %XMM12<imp-def,dead>, %XMM13<imp-def,dead>,
%XMM14<imp-def,dead>, %XMM15<imp-def,dead>, %EFLAGS<imp-def,dead>,
%EAX<imp-def>, %ECX<imp-def,dead>, %EDI<imp-def,dead>,
%EDX<imp-def,dead>, %ESI<imp-def,dead>
108     ADJCALLSTACKUP 0, 0, %ESP<imp-def>, %EFLAGS<imp-def,dead>, %ESP<imp-use>
116     %reg1029<def,dead> = MOV32rr %EAX, %RAX<imp-use,kill>
124     %reg1030<def> = MOV32r0 %EFLAGS<imp-def,dead>
132     %EAX<def> = MOV32rr %reg1030<kill>
140     RET %EAX<imp-use,kill>, %AX<imp-use,kill>


********** REGISTER MAP **********
[reg1024 -> EAX]
[reg1025 -> R10]
[reg1026 -> AH]
[reg1027 -> XMM10]
[reg1028 -> R10]
[reg1029 -> EAX]
[reg1030 -> EAX]


The failure occurs when the spiller tries to eliminate the assignment

116     %reg1029<def,dead> = MOV32rr %EAX, %RAX<imp-use,kill>

after reg1029 is assigned EAX. It occurs because EAX isn't listed as
killed, so InvalidateKills doesn't return it in KillRegs (but does
return RAX).

Is this a bug (was EAX supposed to be marked killed?), or was the
register allocator supposed to mark EAX as killed? (doesn't seem as if
it should - it was killed before regalloc got involved).
Or have I missed something else?

bugpoint produced bytecode is attached, but I don't suppose it's much
help without the allocator. That's packaged as an LLVM project at the
moment - so if it'll help you debug I can send you a copy.

Cheers,
Lang.




--------- Bugpoint reduced bytecode from
SingleSource/Vector/Output/build.llvm.bc ---------

; ModuleID = 'bugpoint-reduced-simplified.bc'
target datalayout =
"e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
target triple = "x86_64-pc-linux-gnu"
@.str1 = external constant [13 x i8]            ; <[13 x i8]*> [#uses=1]

declare i32 @printf(i8* noalias, ...) nounwind

define i32 @main(i32 %argc, i8** %Argv) nounwind {
entry:
        %tmp25.i14 = call i32 (i8*, ...)* @printf( i8* noalias
getelementptr ([13 x i8]* @.str1, i32 0, i64 0), double 0.000000e+00,
double 0.000000e+00, double 0.000000e+00, double 0.000000e+00 )
nounwind           ; <i32> [#uses=0]
        ret i32 0
}