move the [Can]EvaluateInDifferentType functions out to InstCombineCasts.cpp
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92469 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index c5ad10f..b9ecaea 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -17,7 +17,215 @@
using namespace llvm;
using namespace PatternMatch;
-// FIXME: InstCombiner::EvaluateInDifferentType!
+/// CanEvaluateInDifferentType - Return true if we can take the specified value
+/// and return it as type Ty without inserting any new casts and without
+/// changing the computed value. This is used by code that tries to decide
+/// whether promoting or shrinking integer operations to wider or smaller types
+/// will allow us to eliminate a truncate or extend.
+///
+/// This is a truncation operation if Ty is smaller than V->getType(), or an
+/// extension operation if Ty is larger.
+///
+/// If CastOpc is a truncation, then Ty will be a type smaller than V. We
+/// should return true if trunc(V) can be computed by computing V in the smaller
+/// type. If V is an instruction, then trunc(inst(x,y)) can be computed as
+/// inst(trunc(x),trunc(y)), which only makes sense if x and y can be
+/// efficiently truncated.
+///
+/// If CastOpc is a sext or zext, we are asking if the low bits of the value can
+/// bit computed in a larger type, which is then and'd or sext_in_reg'd to get
+/// the final result.
+bool InstCombiner::CanEvaluateInDifferentType(Value *V, const Type *Ty,
+ unsigned CastOpc,
+ int &NumCastsRemoved){
+ // We can always evaluate constants in another type.
+ if (isa<Constant>(V))
+ return true;
+
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (!I) return false;
+
+ const Type *OrigTy = V->getType();
+
+ // If this is an extension or truncate, we can often eliminate it.
+ if (isa<TruncInst>(I) || isa<ZExtInst>(I) || isa<SExtInst>(I)) {
+ // If this is a cast from the destination type, we can trivially eliminate
+ // it, and this will remove a cast overall.
+ if (I->getOperand(0)->getType() == Ty) {
+ // If the first operand is itself a cast, and is eliminable, do not count
+ // this as an eliminable cast. We would prefer to eliminate those two
+ // casts first.
+ if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse())
+ ++NumCastsRemoved;
+ return true;
+ }
+ }
+
+ // We can't extend or shrink something that has multiple uses: doing so would
+ // require duplicating the instruction in general, which isn't profitable.
+ if (!I->hasOneUse()) return false;
+
+ unsigned Opc = I->getOpcode();
+ switch (Opc) {
+ case Instruction::Add:
+ case Instruction::Sub:
+ case Instruction::Mul:
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor:
+ // These operators can all arbitrarily be extended or truncated.
+ return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
+ NumCastsRemoved) &&
+ CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
+ NumCastsRemoved);
+
+ case Instruction::UDiv:
+ case Instruction::URem: {
+ // UDiv and URem can be truncated if all the truncated bits are zero.
+ uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
+ uint32_t BitWidth = Ty->getScalarSizeInBits();
+ if (BitWidth < OrigBitWidth) {
+ APInt Mask = APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth);
+ if (MaskedValueIsZero(I->getOperand(0), Mask) &&
+ MaskedValueIsZero(I->getOperand(1), Mask)) {
+ return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
+ NumCastsRemoved) &&
+ CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
+ NumCastsRemoved);
+ }
+ }
+ break;
+ }
+ case Instruction::Shl:
+ // If we are truncating the result of this SHL, and if it's a shift of a
+ // constant amount, we can always perform a SHL in a smaller type.
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
+ uint32_t BitWidth = Ty->getScalarSizeInBits();
+ if (BitWidth < OrigTy->getScalarSizeInBits() &&
+ CI->getLimitedValue(BitWidth) < BitWidth)
+ return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
+ NumCastsRemoved);
+ }
+ break;
+ case Instruction::LShr:
+ // If this is a truncate of a logical shr, we can truncate it to a smaller
+ // lshr iff we know that the bits we would otherwise be shifting in are
+ // already zeros.
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
+ uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
+ uint32_t BitWidth = Ty->getScalarSizeInBits();
+ if (BitWidth < OrigBitWidth &&
+ MaskedValueIsZero(I->getOperand(0),
+ APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
+ CI->getLimitedValue(BitWidth) < BitWidth) {
+ return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
+ NumCastsRemoved);
+ }
+ }
+ break;
+ case Instruction::ZExt:
+ case Instruction::SExt:
+ case Instruction::Trunc:
+ // If this is the same kind of case as our original (e.g. zext+zext), we
+ // can safely replace it. Note that replacing it does not reduce the number
+ // of casts in the input.
+ if (Opc == CastOpc)
+ return true;
+
+ // sext (zext ty1), ty2 -> zext ty2
+ if (CastOpc == Instruction::SExt && Opc == Instruction::ZExt)
+ return true;
+ break;
+ case Instruction::Select: {
+ SelectInst *SI = cast<SelectInst>(I);
+ return CanEvaluateInDifferentType(SI->getTrueValue(), Ty, CastOpc,
+ NumCastsRemoved) &&
+ CanEvaluateInDifferentType(SI->getFalseValue(), Ty, CastOpc,
+ NumCastsRemoved);
+ }
+ case Instruction::PHI: {
+ // We can change a phi if we can change all operands.
+ PHINode *PN = cast<PHINode>(I);
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (!CanEvaluateInDifferentType(PN->getIncomingValue(i), Ty, CastOpc,
+ NumCastsRemoved))
+ return false;
+ return true;
+ }
+ default:
+ // TODO: Can handle more cases here.
+ break;
+ }
+
+ return false;
+}
+
+/// EvaluateInDifferentType - Given an expression that
+/// CanEvaluateInDifferentType returns true for, actually insert the code to
+/// evaluate the expression.
+Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty,
+ bool isSigned) {
+ if (Constant *C = dyn_cast<Constant>(V))
+ return ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
+
+ // Otherwise, it must be an instruction.
+ Instruction *I = cast<Instruction>(V);
+ Instruction *Res = 0;
+ unsigned Opc = I->getOpcode();
+ switch (Opc) {
+ case Instruction::Add:
+ case Instruction::Sub:
+ case Instruction::Mul:
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor:
+ case Instruction::AShr:
+ case Instruction::LShr:
+ case Instruction::Shl:
+ case Instruction::UDiv:
+ case Instruction::URem: {
+ Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
+ Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
+ Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
+ break;
+ }
+ case Instruction::Trunc:
+ case Instruction::ZExt:
+ case Instruction::SExt:
+ // If the source type of the cast is the type we're trying for then we can
+ // just return the source. There's no need to insert it because it is not
+ // new.
+ if (I->getOperand(0)->getType() == Ty)
+ return I->getOperand(0);
+
+ // Otherwise, must be the same type of cast, so just reinsert a new one.
+ Res = CastInst::Create(cast<CastInst>(I)->getOpcode(), I->getOperand(0),Ty);
+ break;
+ case Instruction::Select: {
+ Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
+ Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned);
+ Res = SelectInst::Create(I->getOperand(0), True, False);
+ break;
+ }
+ case Instruction::PHI: {
+ PHINode *OPN = cast<PHINode>(I);
+ PHINode *NPN = PHINode::Create(Ty);
+ for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) {
+ Value *V =EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned);
+ NPN->addIncoming(V, OPN->getIncomingBlock(i));
+ }
+ Res = NPN;
+ break;
+ }
+ default:
+ // TODO: Can handle more cases here.
+ llvm_unreachable("Unreachable!");
+ break;
+ }
+
+ Res->takeName(I);
+ return InsertNewInstBefore(Res, *I);
+}
/// This function is a wrapper around CastInst::isEliminableCastPair. It