Array accesses are independent if the underlying arrays differ.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74499 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/LoopDependenceAnalysis.cpp b/lib/Analysis/LoopDependenceAnalysis.cpp
index 020a8c7..c1168ec 100644
--- a/lib/Analysis/LoopDependenceAnalysis.cpp
+++ b/lib/Analysis/LoopDependenceAnalysis.cpp
@@ -22,6 +22,7 @@
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Instructions.h"
+#include "llvm/Support/Debug.h"
using namespace llvm;
LoopPass *llvm::createLoopDependenceAnalysisPass() {
@@ -51,6 +52,20 @@
memrefs.push_back(i);
}
+static bool IsLoadOrStoreInst(Value *I) {
+ return isa<LoadInst>(I) || isa<StoreInst>(I);
+}
+
+static Value *GetPointerOperand(Value *I) {
+ if (LoadInst *i = dyn_cast<LoadInst>(I))
+ return i->getPointerOperand();
+ if (StoreInst *i = dyn_cast<StoreInst>(I))
+ return i->getPointerOperand();
+ assert(0 && "Value is no load or store instruction!");
+ // Never reached.
+ return 0;
+}
+
//===----------------------------------------------------------------------===//
// Dependence Testing
//===----------------------------------------------------------------------===//
@@ -65,6 +80,38 @@
bool LoopDependenceAnalysis::depends(Value *src, Value *dst) {
assert(isDependencePair(src, dst) && "Values form no dependence pair!");
+ DOUT << "== LDA test ==\n" << *src << *dst;
+
+ // We only analyse loads and stores; for possible memory accesses by e.g.
+ // free, call, or invoke instructions we conservatively assume dependence.
+ if (!IsLoadOrStoreInst(src) || !IsLoadOrStoreInst(dst))
+ return true;
+
+ Value *srcPtr = GetPointerOperand(src);
+ Value *dstPtr = GetPointerOperand(dst);
+ const Value *srcObj = srcPtr->getUnderlyingObject();
+ const Value *dstObj = dstPtr->getUnderlyingObject();
+ const Type *srcTy = srcObj->getType();
+ const Type *dstTy = dstObj->getType();
+
+ // For now, we only work on (pointers to) global or stack-allocated array
+ // values, as we know that their underlying memory areas will not overlap.
+ // MAYBE: relax this and test for aliasing?
+ if (!((isa<GlobalVariable>(srcObj) || isa<AllocaInst>(srcObj)) &&
+ (isa<GlobalVariable>(dstObj) || isa<AllocaInst>(dstObj)) &&
+ isa<PointerType>(srcTy) &&
+ isa<PointerType>(dstTy) &&
+ isa<ArrayType>(cast<PointerType>(srcTy)->getElementType()) &&
+ isa<ArrayType>(cast<PointerType>(dstTy)->getElementType())))
+ return true;
+
+ // If the arrays are different, the underlying memory areas do not overlap
+ // and the memory accesses are therefore independent.
+ if (srcObj != dstObj)
+ return false;
+
+ // We couldn't establish a more precise result, so we have to conservatively
+ // assume full dependence.
return true;
}