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Memory Dependence Analysis (not mem-dep test) take advantage of "invariant.load" metadata.

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The "invariant.load" metadata indicates the memory unit being accessed is immutable.
A load annotated with this metadata can be moved across any store.

As I am not sure if it is legal to move such loads across barrier/fence, this
change dose not allow such transformation.

rdar://11311484

Thank Arnold for code review.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176562 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Shuxin Yang
2013-03-06 17:48:48 +00:00
parent 186d8a3d67
commit 985dac6579
5 changed files with 55 additions and 7 deletions
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18
lib/Analysis/MemoryDependenceAnalysis.cpp
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@@ -351,15 +351,23 @@ getLoadLoadClobberFullWidthSize(const Value *MemLocBase, int64_t MemLocOffs,
/// getPointerDependencyFrom - Return the instruction on which a memory
/// location depends. If isLoad is true, this routine ignores may-aliases with
/// read-only operations. If isLoad is false, this routine ignores may-aliases
/// with reads from read-only locations.
/// with reads from read-only locations. If possible, pass the query
/// instruction as well; this function may take advantage of the metadata
/// annotated to the query instruction to refine the result.
MemDepResult MemoryDependenceAnalysis::
getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
BasicBlock::iterator ScanIt, BasicBlock *BB) {
BasicBlock::iterator ScanIt, BasicBlock *BB,
Instruction *QueryInst) {
const Value *MemLocBase = 0;
int64_t MemLocOffset = 0;
unsigned Limit = BlockScanLimit;
bool isInvariantLoad = false;
if (isLoad && QueryInst) {
LoadInst *LI = dyn_cast<LoadInst>(QueryInst);
if (LI && LI->getMetadata(LLVMContext::MD_invariant_load) != 0)
isInvariantLoad = true;
}
// Walk backwards through the basic block, looking for dependencies.
while (ScanIt != BB->begin()) {
@@ -474,6 +482,8 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
continue;
if (R == AliasAnalysis::MustAlias)
return MemDepResult::getDef(Inst);
if (isInvariantLoad)
continue;
return MemDepResult::getClobber(Inst);
}
@@ -571,7 +581,7 @@ MemDepResult MemoryDependenceAnalysis::getDependency(Instruction *QueryInst) {
isLoad |= II->getIntrinsicID() == Intrinsic::lifetime_start;
LocalCache = getPointerDependencyFrom(MemLoc, isLoad, ScanPos,
QueryParent);
QueryParent, QueryInst);
} else if (isa<CallInst>(QueryInst) || isa<InvokeInst>(QueryInst)) {
CallSite QueryCS(QueryInst);
bool isReadOnly = AA->onlyReadsMemory(QueryCS);