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Enhance GVN to do more precise alias queries for non-local memory

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references. For example, this allows gvn to eliminate the load in
this example:

  void foo(int n, int* p, int *q) {
    p[0] = 0;
    p[1] = 1;
    if (n) {
      *q = p[0];
    }
  }


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118714 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2010-11-10 20:37:15 +00:00
parent af3d38f70e
commit 075fb5d68f
6 changed files with 129 additions and 27 deletions
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47
lib/Analysis/MemoryDependenceAnalysis.cpp
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@ -741,16 +741,40 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
// Look up the cached info for Pointer.
ValueIsLoadPair CacheKey(Pointer.getAddr(), isLoad);
NonLocalPointerInfo *CacheInfo = &NonLocalPointerDeps[CacheKey];
// If this query's TBAATag is inconsistent with the cached one, discard the
// tag and restart the query.
if (CacheInfo->TBAATag != Loc.TBAATag) {
CacheInfo->TBAATag = 0;
NonLocalPointerDeps.erase(CacheKey);
return getNonLocalPointerDepFromBB(Pointer, Loc.getWithoutTBAATag(),
isLoad, StartBB, Result, Visited,
SkipFirstBlock);
// Set up a temporary NLPI value. If the map doesn't yet have an entry for
// CacheKey, this value will be inserted as the associated value. Otherwise,
// it'll be ignored, and we'll have to check to see if the cached size and
// tbaa tag are consistent with the current query.
NonLocalPointerInfo InitialNLPI;
InitialNLPI.Size = Loc.Size;
InitialNLPI.TBAATag = Loc.TBAATag;
// Get the NLPI for CacheKey, inserting one into the map if it doesn't
// already have one.
std::pair<CachedNonLocalPointerInfo::iterator, bool> Pair =
NonLocalPointerDeps.insert(std::make_pair(CacheKey, InitialNLPI));
NonLocalPointerInfo *CacheInfo = &Pair.first->second;
if (!Pair.second) {
// If this query's Size is inconsistent with the cached one, take the
// maximum size and restart the query.
if (CacheInfo->Size != Loc.Size) {
CacheInfo->Size = std::max(CacheInfo->Size, Loc.Size);
return getNonLocalPointerDepFromBB(Pointer,
Loc.getWithNewSize(CacheInfo->Size),
isLoad, StartBB, Result, Visited,
SkipFirstBlock);
}
// If this query's TBAATag is inconsistent with the cached one, discard the
// tag and restart the query.
if (CacheInfo->TBAATag != Loc.TBAATag) {
CacheInfo->TBAATag = 0;
return getNonLocalPointerDepFromBB(Pointer, Loc.getWithoutTBAATag(),
isLoad, StartBB, Result, Visited,
SkipFirstBlock);
}
}
NonLocalDepInfo *Cache = &CacheInfo->NonLocalDeps;
@ -796,6 +820,7 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
CacheInfo->Pair = BBSkipFirstBlockPair(StartBB, SkipFirstBlock);
else {
CacheInfo->Pair = BBSkipFirstBlockPair();
CacheInfo->Size = 0;
CacheInfo->TBAATag = 0;
}
@ -921,6 +946,7 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
// cached value to do more work but not miss the phi trans failure.
NonLocalPointerInfo &NLPI = NonLocalPointerDeps[CacheKey];
NLPI.Pair = BBSkipFirstBlockPair();
NLPI.Size = 0;
NLPI.TBAATag = 0;
continue;
}
@ -949,6 +975,7 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
// specific block queries) but we can't do the fastpath "return all
// results from the set" Clear out the indicator for this.
CacheInfo->Pair = BBSkipFirstBlockPair();
CacheInfo->Size = 0;
CacheInfo->TBAATag = 0;
SkipFirstBlock = false;
continue;
@ -967,6 +994,7 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
// specific block queries) but we can't do the fastpath "return all
// results from the set". Clear out the indicator for this.
CacheInfo->Pair = BBSkipFirstBlockPair();
CacheInfo->Size = 0;
CacheInfo->TBAATag = 0;
// If *nothing* works, mark the pointer as being clobbered by the first
@ -1184,6 +1212,7 @@ void MemoryDependenceAnalysis::removeInstruction(Instruction *RemInst) {
// The cache is not valid for any specific block anymore.
NonLocalPointerDeps[P].Pair = BBSkipFirstBlockPair();
NonLocalPointerDeps[P].Size = 0;
NonLocalPointerDeps[P].TBAATag = 0;
// Update any entries for RemInst to use the instruction after it.