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my recent change caused a failure in a bswap testcase, because it changed

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the order that instcombine processed instructions in the testcase.  The end
result is that instcombine finished with:

define i16 @test1(i16 %a) {
        %tmp = zext i16 %a to i32               ; <i32> [#uses=2]
        %tmp21 = lshr i32 %tmp, 8               ; <i32> [#uses=1]
        %tmp5 = shl i32 %tmp, 8         ; <i32> [#uses=1]
        %tmp.upgrd.32 = or i32 %tmp21, %tmp5            ; <i32> [#uses=1]
        %tmp.upgrd.3 = trunc i32 %tmp.upgrd.32 to i16           ; <i16> [#uses=1]
        ret i16 %tmp.upgrd.3
}

which can't get matched as a bswap.

This patch makes instcombine more sophisticated about removing truncating
casts, allowing it to turn this into:

define i16 @test2(i16 %a) {
        %tmp211 = lshr i16 %a, 8
        %tmp52 = shl i16 %a, 8
        %tmp.upgrd.323 = or i16 %tmp211, %tmp52
        ret i16 %tmp.upgrd.323
}

which then matches as bswap.  This fixes bswap.ll and implements
InstCombine/cast2.ll:test[12].  This also implements cast elimination of
add/sub.

llvm-svn: 34870
This commit is contained in:
Chris Lattner 2007-03-03 05:27:34 +00:00
parent e1179e62fb
commit f22da20af4
1 changed files with 71 additions and 48 deletions
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119
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -5908,35 +5908,62 @@ Instruction *InstCombiner::PromoteCastOfAllocation(CastInst &CI,
}
/// CanEvaluateInDifferentType - Return true if we can take the specified value
/// and return it without inserting any new casts. 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.
static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
/// 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.
static bool CanEvaluateInDifferentType(Value *V, const IntegerType *Ty,
int &NumCastsRemoved) {
if (isa<Constant>(V)) return true;
// We can always evaluate constants in another type.
if (isa<ConstantInt>(V))
return true;
Instruction *I = dyn_cast<Instruction>(V);
if (!I || !I->hasOneUse()) return false;
if (!I) return false;
const IntegerType *OrigTy = cast<IntegerType>(V->getType());
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
if (!I->hasOneUse()) return false;
// These operators can all arbitrarily be extended or truncated.
return CanEvaluateInDifferentType(I->getOperand(0), Ty, NumCastsRemoved) &&
CanEvaluateInDifferentType(I->getOperand(1), Ty, NumCastsRemoved);
case Instruction::AShr:
case Instruction::LShr:
case Instruction::Shl:
// If this is just a bitcast changing the sign of the operation, we can
// convert if the operand can be converted.
if (V->getType()->getPrimitiveSizeInBits() == Ty->getPrimitiveSizeInBits())
return CanEvaluateInDifferentType(I->getOperand(0), Ty, NumCastsRemoved);
if (!I->hasOneUse()) return false;
// 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))) {
if (Ty->getBitWidth() < OrigTy->getBitWidth() &&
CI->getZExtValue() < Ty->getBitWidth())
return CanEvaluateInDifferentType(I->getOperand(0), Ty,NumCastsRemoved);
}
break;
case Instruction::LShr:
if (!I->hasOneUse()) return false;
// 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))) {
if (Ty->getBitWidth() < OrigTy->getBitWidth() &&
MaskedValueIsZero(I->getOperand(0),
OrigTy->getBitMask() & ~Ty->getBitMask()) &&
CI->getZExtValue() < Ty->getBitWidth()) {
return CanEvaluateInDifferentType(I->getOperand(0), Ty, NumCastsRemoved);
}
}
break;
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::BitCast:
// 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) {
@ -5962,7 +5989,7 @@ static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
/// CanEvaluateInDifferentType returns true for, actually insert the code to
/// evaluate the expression.
Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty,
bool isSigned ) {
bool isSigned) {
if (Constant *C = dyn_cast<Constant>(V))
return ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
@ -5970,21 +5997,18 @@ Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty,
Instruction *I = cast<Instruction>(V);
Instruction *Res = 0;
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor: {
Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
Res = BinaryOperator::create((Instruction::BinaryOps)I->getOpcode(),
LHS, RHS, I->getName());
break;
}
case Instruction::Xor:
case Instruction::AShr:
case Instruction::LShr:
case Instruction::Shl: {
Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
Res = BinaryOperator::create(Instruction::BinaryOps(I->getOpcode()), LHS,
I->getOperand(1), I->getName());
Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
Res = BinaryOperator::create((Instruction::BinaryOps)I->getOpcode(),
LHS, RHS, I->getName());
break;
}
case Instruction::Trunc:
@ -6066,8 +6090,8 @@ Instruction *InstCombiner::commonCastTransforms(CastInst &CI) {
return 0;
}
/// Only the TRUNC, ZEXT, SEXT, and BITCONVERT can have both operands as
/// integers. This function implements the common transforms for all those
/// Only the TRUNC, ZEXT, SEXT, and BITCAST can both operand and result as
/// integer types. This function implements the common transforms for all those
/// cases.
/// @brief Implement the transforms common to CastInst with integer operands
Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
@ -6093,9 +6117,11 @@ Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
if (!SrcI || !Src->hasOneUse())
return 0;
// Attempt to propagate the cast into the instruction.
// Attempt to propagate the cast into the instruction for int->int casts.
int NumCastsRemoved = 0;
if (CanEvaluateInDifferentType(SrcI, DestTy, NumCastsRemoved)) {
if (!isa<BitCastInst>(CI) &&
CanEvaluateInDifferentType(SrcI, cast<IntegerType>(DestTy),
NumCastsRemoved)) {
// If this cast is a truncate, evaluting in a different type always
// eliminates the cast, so it is always a win. If this is a noop-cast
// this just removes a noop cast which isn't pointful, but simplifies
@ -6104,27 +6130,24 @@ Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
// the input have eliminated at least one cast. If this is a sign
// extension, we insert two new casts (to do the extension) so we
// require that two casts have been eliminated.
bool DoXForm = CI.isNoopCast(TD->getIntPtrType());
if (!DoXForm) {
switch (CI.getOpcode()) {
case Instruction::Trunc:
DoXForm = true;
break;
case Instruction::ZExt:
DoXForm = NumCastsRemoved >= 1;
break;
case Instruction::SExt:
DoXForm = NumCastsRemoved >= 2;
break;
case Instruction::BitCast:
DoXForm = false;
break;
default:
// All the others use floating point so we shouldn't actually
// get here because of the check above.
assert(!"Unknown cast type .. unreachable");
break;
}
bool DoXForm;
switch (CI.getOpcode()) {
default:
// All the others use floating point so we shouldn't actually
// get here because of the check above.
assert(0 && "Unknown cast type");
case Instruction::Trunc:
DoXForm = true;
break;
case Instruction::ZExt:
DoXForm = NumCastsRemoved >= 1;
break;
case Instruction::SExt:
DoXForm = NumCastsRemoved >= 2;
break;
case Instruction::BitCast:
DoXForm = false;
break;
}
if (DoXForm) {