[LLVMdev] Eliminating redundant loads

[Dibyendu Majumdar]

On 22 February 2015 at 22:54, Hal Finkel <hfinkel at anl.gov> wrote:
>> I tried setting the module's DataLayout  to the engine's DataLayout.
>> Don't see any improvement.
>> The memcpy() is to perform a struct assign, so I tried replacing that
>> with member by member store.
>> But even then the loads are not being eliminated so I guess the
>> memcpy() isn't the issue.
>
> If you run the IR through opt -O3 do you get the optimization you expect?
>

Hi,
Tried that - no improvement.

Also tried removing the redundant GEP instructions, leaving just the
loads. Here is a dump that shows the output after running the
optimizer passes (this is from the passes in my program not opt -O3;
this version does not use memcpy() either):

  %L_ci = getelementptr inbounds %ravi.lua_State* %L, i64 0, i32 6
  %0 = load %ravi.CallInfo** %L_ci, align 8
  %base = getelementptr inbounds %ravi.CallInfo* %0, i64 0, i32 4, i32 0
  %1 = bitcast %ravi.CallInfo* %0 to %ravi.LClosure***
  %2 = load %ravi.LClosure*** %1, align 8
  %3 = load %ravi.LClosure** %2, align 8
  %Proto = getelementptr inbounds %ravi.LClosure* %3, i64 0, i32 5
  %4 = load %ravi.Proto** %Proto, align 8
  %k = getelementptr inbounds %ravi.Proto* %4, i64 0, i32 14
  %5 = load %ravi.TValue** %k, align 8
  %6 = load %ravi.TValue** %base, align 8
  %srcvalue = getelementptr inbounds %ravi.TValue* %5, i64 0, i32 0, i32 0
  %destvalue = getelementptr inbounds %ravi.TValue* %6, i64 0, i32 0, i32 0
  %7 = load double* %srcvalue, align 8
  store double %7, double* %destvalue, align 8
  %srctype = getelementptr inbounds %ravi.TValue* %5, i64 0, i32 1
  %desttype = getelementptr inbounds %ravi.TValue* %6, i64 0, i32 1
  %8 = load i32* %srctype, align 4
  store i32 %8, i32* %desttype, align 4
  %9 = load %ravi.TValue** %base, align 8
  %srcvalue1 = getelementptr inbounds %ravi.TValue* %5, i64 1, i32 0, i32 0
  %destvalue2 = getelementptr inbounds %ravi.TValue* %9, i64 1, i32 0, i32 0
  %10 = load double* %srcvalue1, align 8
  store double %10, double* %destvalue2, align 8


Regards
Dibyendu