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
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 @@
/// 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 @@
continue;
if (R == AliasAnalysis::MustAlias)
return MemDepResult::getDef(Inst);
+ if (isInvariantLoad)
+ continue;
return MemDepResult::getClobber(Inst);
}
@@ -571,7 +581,7 @@
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);