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author | Shuxin Yang <shuxin.llvm@gmail.com> | 2013-03-06 17:48:48 +0000 |
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committer | Shuxin Yang <shuxin.llvm@gmail.com> | 2013-03-06 17:48:48 +0000 |
commit | 985dac65791b9f6f631bdd51c18fe66592a67469 (patch) | |
tree | 9265b2aa99cf3753755535652b74ad4683c4bcaf /lib/Analysis | |
parent | 186d8a3d67ccd2b2401c5d7d4e2cc15c4d1fdeae (diff) | |
download | external_llvm-985dac65791b9f6f631bdd51c18fe66592a67469.zip external_llvm-985dac65791b9f6f631bdd51c18fe66592a67469.tar.gz external_llvm-985dac65791b9f6f631bdd51c18fe66592a67469.tar.bz2 |
Memory Dependence Analysis (not mem-dep test) take advantage of "invariant.load" metadata.
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
Diffstat (limited to 'lib/Analysis')
-rw-r--r-- | lib/Analysis/MemoryDependenceAnalysis.cpp | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp index 38bf5dd..1faa046 100644 --- a/lib/Analysis/MemoryDependenceAnalysis.cpp +++ b/lib/Analysis/MemoryDependenceAnalysis.cpp @@ -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); |