[llvm-commits] [llvm] r128332 - /llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp

[Bill Wendling]

It was added earlier (see r128319). And there's all ready a test directory for DSE.

-bw

On Mar 26, 2011, at 1:12 AM, Cameron Zwarich wrote:

> Test?
> 
> Cameron
> 
> On 2011-03-26, at 1:02 AM, Bill Wendling wrote:
> 
>> Author: void
>> Date: Sat Mar 26 03:02:59 2011
>> New Revision: 128332
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=128332&view=rev
>> Log:
>> Rework the logic that determines if a store completely overlaps an ealier store.
>> 
>> There are two ways that a later store can comletely overlap a previous store:
>> 
>> 1. They both start at the same offset, but the earlier store's size is <= the
>>  later's size, or
>> 2. The earlier store's offset is > the later's offset, but it's offset + size
>>  doesn't extend past the later's offset + size.
>> 
>> Modified:
>>   llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
>> 
>> Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=128332&r1=128331&r2=128332&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Sat Mar 26 03:02:59 2011
>> @@ -340,26 +340,34 @@
>>  // Okay, we have stores to two completely different pointers.  Try to
>>  // decompose the pointer into a "base + constant_offset" form.  If the base
>>  // pointers are equal, then we can reason about the two stores.
>> -  int64_t Off1 = 0, Off2 = 0;
>> -  const Value *BP1 = GetPointerBaseWithConstantOffset(P1, Off1, TD);
>> -  const Value *BP2 = GetPointerBaseWithConstantOffset(P2, Off2, TD);
>> +  int64_t EarlierOff = 0, LaterOff = 0;
>> +  const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, TD);
>> +  const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, TD);
>> 
>>  // If the base pointers still differ, we have two completely different stores.
>>  if (BP1 != BP2)
>>    return false;
>> -  
>> -  // Otherwise, we might have a situation like:
>> -  //  store i16 -> P + 1 Byte
>> -  //  store i32 -> P
>> -  // In this case, we see if the later store completely overlaps all bytes
>> -  // stored by the previous store.
>> -  if (Off1 < Off2 ||                       // Earlier starts before Later.
>> -      Off2 < 0 ||                          // Later is -.
>> -      Off1+Earlier.Size > Off2+Later.Size) // Earlier goes beyond Later.
>> -    return false;
>> 
>> -  // Otherwise, we have complete overlap.
>> -  return true;
>> +  // The later store completely overlaps the earlier store if:
>> +  // 
>> +  // 1. Both start at the same offset and the later one's size is greater than
>> +  //    or equal to the earlier one's, or
>> +  //
>> +  //      |--earlier--|
>> +  //      |--   later   --|
>> +  //      
>> +  // 2. The earlier store has an offset greater than the later offset, but which
>> +  //    still lies completely within the later store.
>> +  //
>> +  //        |--earlier--|
>> +  //    |-----  later  ------|
>> +  if ((EarlierOff == LaterOff && Earlier.Size <= Later.Size) ||
>> +      (EarlierOff > LaterOff &&
>> +       EarlierOff + Earlier.Size <= LaterOff + Later.Size))
>> +    return true;
>> +
>> +  // Otherwise, they don't completely overlap.
>> +  return false;
>> }
>> 
>> /// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a
>> 
>> 
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