#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
static bool isCompleteOverwrite(const AliasAnalysis::Location &Later,
const AliasAnalysis::Location &Earlier,
AliasAnalysis &AA) {
- const Value *P1 = Later.Ptr->stripPointerCasts();
- const Value *P2 = Earlier.Ptr->stripPointerCasts();
+ const Value *P1 = Earlier.Ptr->stripPointerCasts();
+ const Value *P2 = Later.Ptr->stripPointerCasts();
- // Make sure that the start pointers are the same.
- if (P1 != P2)
- return false;
-
- // If we don't know the sizes of either access, then we can't do a comparison.
+ // If the start pointers are the same, we just have to compare sizes to see if
+ // the later store was larger than the earlier store.
+ if (P1 == P2) {
+ // If we don't know the sizes of either access, then we can't do a
+ // comparison.
+ if (Later.Size == AliasAnalysis::UnknownSize ||
+ Earlier.Size == AliasAnalysis::UnknownSize) {
+ // If we have no TargetData information around, then the size of the store
+ // is inferrable from the pointee type. If they are the same type, then
+ // we know that the store is safe.
+ if (AA.getTargetData() == 0)
+ return Later.Ptr->getType() == Earlier.Ptr->getType();
+ return false;
+ }
+
+ // Make sure that the Later size is >= the Earlier size.
+ if (Later.Size < Earlier.Size)
+ return false;
+ return true;
+ }
+
+ // Otherwise, we have to have size information, and the later store has to be
+ // larger than the earlier one.
if (Later.Size == AliasAnalysis::UnknownSize ||
- Earlier.Size == AliasAnalysis::UnknownSize) {
- // If we have no TargetData information around, then the size of the store
- // is inferrable from the pointee type. If they are the same type, then we
- // know that the store is safe.
- if (AA.getTargetData() == 0)
- return Later.Ptr->getType() == Earlier.Ptr->getType();
+ Earlier.Size == AliasAnalysis::UnknownSize ||
+ Later.Size <= Earlier.Size ||
+ AA.getTargetData() == 0)
return false;
- }
- // Make sure that the Later size is >= the Earlier size.
- if (Later.Size < Earlier.Size)
+ const TargetData &TD = *AA.getTargetData();
+
+ // Okay, we have stores to two completely different pointers. Try to
+ // decompose the pointer into a "base + constant_offset" form. If the base
+ // pointers are equal, then we can reason about the two stores.
+ int64_t Off1 = 0, Off2 = 0;
+ const Value *BP1 = GetPointerBaseWithConstantOffset(P1, Off1, TD);
+ const Value *BP2 = GetPointerBaseWithConstantOffset(P2, Off2, TD);
+
+ // If the base pointers still differ, we have two completely different stores.
+ if (BP1 != BP2)
return false;
+ // Otherwise, we might have a situation like:
+ // store i16 -> P + 1 Byte
+ // store i32 -> P
+ // In this case, we see if the later store completely overlaps all bytes
+ // stored by the previous store.
+ if (Off1 < Off2 || // Earlier starts before Later.
+ Off1+Earlier.Size > Off2+Later.Size) // Earlier goes beyond Later.
+ return false;
+ // Otherwise, we have complete overlap.
return true;
}