+/// doesClobberMemory - Does this instruction clobber (write without reading)
+/// some memory?
+static bool doesClobberMemory(Instruction *I) {
+ if (isa<StoreInst>(I))
+ return true;
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+ switch (II->getIntrinsicID()) {
+ default:
+ return false;
+ case Intrinsic::memset:
+ case Intrinsic::memmove:
+ case Intrinsic::memcpy:
+ case Intrinsic::init_trampoline:
+ case Intrinsic::lifetime_end:
+ return true;
+ }
+ }
+ return false;
+}
+
+/// isElidable - If the value of this instruction and the memory it writes to is
+/// unused, may we delete this instrtction?
+static bool isElidable(Instruction *I) {
+ assert(doesClobberMemory(I));
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+ return II->getIntrinsicID() != Intrinsic::lifetime_end;
+ if (StoreInst *SI = dyn_cast<StoreInst>(I))
+ return !SI->isVolatile();
+ return true;
+}
+
+/// getPointerOperand - Return the pointer that is being clobbered.
+static Value *getPointerOperand(Instruction *I) {
+ assert(doesClobberMemory(I));
+ if (StoreInst *SI = dyn_cast<StoreInst>(I))
+ return SI->getPointerOperand();
+ if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I))
+ return MI->getOperand(1);
+
+ switch (cast<IntrinsicInst>(I)->getIntrinsicID()) {
+ default: assert(false && "Unexpected intrinsic!");
+ case Intrinsic::init_trampoline:
+ return I->getOperand(1);
+ case Intrinsic::lifetime_end:
+ return I->getOperand(2);
+ }
+}
+
+/// getStoreSize - Return the length in bytes of the write by the clobbering
+/// instruction. If variable or unknown, returns -1.
+static unsigned getStoreSize(Instruction *I, const TargetData *TD) {
+ assert(doesClobberMemory(I));
+ if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+ if (!TD) return -1u;
+ return TD->getTypeStoreSize(SI->getOperand(0)->getType());
+ }
+
+ Value *Len;
+ if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
+ Len = MI->getLength();
+ } else {
+ switch (cast<IntrinsicInst>(I)->getIntrinsicID()) {
+ default: assert(false && "Unexpected intrinsic!");
+ case Intrinsic::init_trampoline:
+ return -1u;
+ case Intrinsic::lifetime_end:
+ Len = I->getOperand(1);
+ break;
+ }
+ }
+ if (ConstantInt *LenCI = dyn_cast<ConstantInt>(Len))
+ if (!LenCI->isAllOnesValue())
+ return LenCI->getZExtValue();
+ return -1u;
+}