[llvm-commits] [llvm] r57257 - /llvm/trunk/lib/Target/X86/X86InstrInfo.td

[Dale Johannesen]

On Oct 7, 2008, at 1:34 PMPDT, Evan Cheng wrote:

> Hi Dale,
>
> I think we ought to fix the bug in the local register allocator
> instead. Is it not checking for aliases or sub-registers somewhere?
>
> Thanks,
>
> Evan

Surely not "instead", the code I changed was clearly wrong.

Here are before-and-after dumps.  I have not tracked it through the  
code, but it looks like it's assuming imp-use physregs are supposed to  
match in type with the definition of that reg.  That seems like a  
reasonable assumption to me since the code generator has complete  
control of those types.

Before

> Starting RegAlloc of: %AX<def,dead> = MOV16rr %reg1029<kill>
>   Regs have values: [AL,%reg1026] [CX,%reg1029]
>   Last use of CX[%reg1029], removing it from live set
>   Last use of CL[%reg1029], removing it from live set
>   Last use of CH[%reg1029], removing it from live set
>   Spilling register AL containing %reg1026 to stack slot #4
>   Register AX [%reg3] is never used, removing it frame live list
>   Register AL [%reg2] is never used, removing it frame live list
>   Register AH [%reg1] is never used, removing it frame live list
>   Register EAX [%reg17] is never used, removing it frame live list
>
> Starting RegAlloc of: DIV8r %reg1026<kill>, %AX<imp-def,dead>,  
> %EFLAGS<imp-def,dead>, %AL<imp-use>, %AH<imp-use,kill>
>   Regs have values:
>   Reloading %reg1026 into AL  <<<<<<<<< wrong
>   Last use of AL[%reg1026], removing it from live set
>   Last use of AH[%reg1], removing it from live set
>   Register AX [%reg3] is never used, removing it frame live list
>   Register AL [%reg2] is never used, removing it frame live list
>   Register AH [%reg1] is never used, removing it frame live list
>   Register EAX [%reg17] is never used, removing it frame live list
>   Register EFLAGS [%reg23] is never used, removing it frame live list


After

> Starting RegAlloc of: %AX<def> = MOV16rr %reg1029<kill>
>   Regs have values: [AL,%reg1026] [CX,%reg1029]
>   Last use of CX[%reg1029], removing it from live set
>   Last use of CL[%reg1029], removing it from live set
>   Last use of CH[%reg1029], removing it from live set
>   Spilling register AL containing %reg1026 to stack slot #4
>
> Starting RegAlloc of: DIV8r %reg1026<kill>, %AL<imp-def>, %AH<imp- 
> def,dead>, %EFLAGS<imp-def,dead>, %AX<imp-use,kill>
>   Regs have values: [AH,%reg0] [AL,%reg0] [AX,%reg0]
>   Reloading %reg1026 into CL
>   Last use of CL[%reg1026], removing it from live set
>   Last use of AX[%reg3], removing it from live set
>   Last use of AL[%reg3], removing it from live set
>   Last use of AH[%reg3], removing it from live set
>   Register AH [%reg1] is never used, removing it frame live list
>   Register AX [%reg3] is never used, removing it frame live list
>   Register EAX [%reg17] is never used, removing it frame live list
>   Register EFLAGS [%reg23] is never used, removing it frame live list

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