[llvm-commits] [llvm] r142202 - /llvm/trunk/lib/CodeGen/MachineLICM.cpp

[Devang Patel]

On Oct 19, 2011, at 4:35 PM, Evan Cheng wrote:

> How about loads from constant pool and other such loads?

We have not found a way to confidently confirm safety of such speculative loads.

> See MachineInstr::isInvariantLoad()?

This is checked as part of whether this load is LICM'able or not.
-
Devang

> 
> Evan
> 
> On Oct 17, 2011, at 10:35 AM, Devang Patel wrote:
> 
>> Author: dpatel
>> Date: Mon Oct 17 12:35:01 2011
>> New Revision: 142202
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=142202&view=rev
>> Log:
>> It is safe to speculate load from GOT. This fixes performance regression caused by r141689.
>> 
>> Radar 10281206.
>> 
>> Modified:
>>   llvm/trunk/lib/CodeGen/MachineLICM.cpp
>> 
>> Modified: llvm/trunk/lib/CodeGen/MachineLICM.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineLICM.cpp?rev=142202&r1=142201&r2=142202&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/CodeGen/MachineLICM.cpp (original)
>> +++ llvm/trunk/lib/CodeGen/MachineLICM.cpp Mon Oct 17 12:35:01 2011
>> @@ -762,6 +762,21 @@
>>  }
>> }
>> 
>> +/// isLoadFromGOT - Return true if this machine instruction loads from
>> +/// global offset table.
>> +static bool isLoadFromGOT(MachineInstr &MI) {
>> +  assert (MI.getDesc().mayLoad() && "Expected MI that loads!");
>> +  for (MachineInstr::mmo_iterator I = MI.memoperands_begin(),
>> +	 E = MI.memoperands_end(); I != E; ++I) {
>> +    if (const Value *V = (*I)->getValue()) {
>> +      if (const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(V))
>> +        if (PSV == PSV->getGOT())
>> +	  return true;
>> +    }
>> +  }
>> +  return false;
>> +}
>> +
>> /// IsLICMCandidate - Returns true if the instruction may be a suitable
>> /// candidate for LICM. e.g. If the instruction is a call, then it's obviously
>> /// not safe to hoist it.
>> @@ -775,7 +790,8 @@
>>  // it dominates all exiting blocks. If it doesn't, then there is a path out of
>>  // the loop which does not execute this load, so we can't hoist it.
>>  // Stores and side effects are already checked by isSafeToMove.
>> -  if (I.getDesc().mayLoad() && !IsGuaranteedToExecute(I.getParent()))
>> +  if (I.getDesc().mayLoad() && !isLoadFromGOT(I) && 
>> +      !IsGuaranteedToExecute(I.getParent()))
>>    return false;
>> 
>>  return true;
>> 
>> 
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>