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For << and >> with C++, detect when all instances are shifting by the same amount.

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In this case, we now emit calls to potentially-specialized functions for the
left/right shifts that take a single integer value for the shift amount.  These
in turn can be matched to the corresponding intrinsics for the SSE target.

Issue #145.
This commit is contained in:
Matt Pharr
2012-01-19 10:04:32 -07:00
parent 3f89295d10
commit 68f6ea8def
6 changed files with 433 additions and 280 deletions
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238
llvmutil.cpp
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@@ -36,7 +36,9 @@
*/
#include "llvmutil.h"
#include "ispc.h"
#include "type.h"
#include <llvm/Instructions.h>
LLVM_TYPE_CONST llvm::Type *LLVMTypes::VoidType = NULL;
LLVM_TYPE_CONST llvm::PointerType *LLVMTypes::VoidPointerType = NULL;
@@ -465,3 +467,239 @@ LLVMBoolVector(const bool *bvec) {
}
return llvm::ConstantVector::get(vals);
}
/** Conservative test to see if two llvm::Values are equal. There are
(potentially many) cases where the two values actually are equal but
this will return false. However, if it does return true, the two
vectors definitely are equal.
@todo This seems to catch all of the cases we currently need it for in
practice, but it's be nice to make it a little more robust/general. In
general, though, a little something called the halting problem means we
won't get all of them.
*/
static bool
lValuesAreEqual(llvm::Value *v0, llvm::Value *v1,
std::vector<llvm::PHINode *> &seenPhi0,
std::vector<llvm::PHINode *> &seenPhi1) {
// Thanks to the fact that LLVM hashes and returns the same pointer for
// constants (of all sorts, even constant expressions), this first test
// actually catches a lot of cases. LLVM's SSA form also helps a lot
// with this..
if (v0 == v1)
return true;
Assert(seenPhi0.size() == seenPhi1.size());
for (unsigned int i = 0; i < seenPhi0.size(); ++i)
if (v0 == seenPhi0[i] && v1 == seenPhi1[i])
return true;
llvm::BinaryOperator *bo0 = llvm::dyn_cast<llvm::BinaryOperator>(v0);
llvm::BinaryOperator *bo1 = llvm::dyn_cast<llvm::BinaryOperator>(v1);
if (bo0 != NULL && bo1 != NULL) {
if (bo0->getOpcode() != bo1->getOpcode())
return false;
return (lValuesAreEqual(bo0->getOperand(0), bo1->getOperand(0),
seenPhi0, seenPhi1) &&
lValuesAreEqual(bo0->getOperand(1), bo1->getOperand(1),
seenPhi0, seenPhi1));
}
llvm::PHINode *phi0 = llvm::dyn_cast<llvm::PHINode>(v0);
llvm::PHINode *phi1 = llvm::dyn_cast<llvm::PHINode>(v1);
if (phi0 != NULL && phi1 != NULL) {
if (phi0->getNumIncomingValues() != phi1->getNumIncomingValues())
return false;
seenPhi0.push_back(phi0);
seenPhi1.push_back(phi1);
unsigned int numIncoming = phi0->getNumIncomingValues();
// Check all of the incoming values: if all of them are all equal,
// then we're good.
bool anyFailure = false;
for (unsigned int i = 0; i < numIncoming; ++i) {
Assert(phi0->getIncomingBlock(i) == phi1->getIncomingBlock(i));
if (!lValuesAreEqual(phi0->getIncomingValue(i),
phi1->getIncomingValue(i), seenPhi0, seenPhi1)) {
anyFailure = true;
break;
}
}
seenPhi0.pop_back();
seenPhi1.pop_back();
return !anyFailure;
}
return false;
}
/** Given an llvm::Value known to be an integer, return its value as
an int64_t.
*/
static int64_t
lGetIntValue(llvm::Value *offset) {
llvm::ConstantInt *intOffset = llvm::dyn_cast<llvm::ConstantInt>(offset);
Assert(intOffset && (intOffset->getBitWidth() == 32 ||
intOffset->getBitWidth() == 64));
return intOffset->getSExtValue();
}
/** This function takes chains of InsertElement instructions along the
lines of:
%v0 = insertelement undef, value_0, i32 index_0
%v1 = insertelement %v1, value_1, i32 index_1
...
%vn = insertelement %vn-1, value_n-1, i32 index_n-1
and initializes the provided elements array such that the i'th
llvm::Value * in the array is the element that was inserted into the
i'th element of the vector.
*/
void
LLVMFlattenInsertChain(llvm::InsertElementInst *ie, int vectorWidth,
llvm::Value **elements) {
for (int i = 0; i < vectorWidth; ++i)
elements[i] = NULL;
while (ie != NULL) {
int64_t iOffset = lGetIntValue(ie->getOperand(2));
Assert(iOffset >= 0 && iOffset < vectorWidth);
Assert(elements[iOffset] == NULL);
elements[iOffset] = ie->getOperand(1);
llvm::Value *insertBase = ie->getOperand(0);
ie = llvm::dyn_cast<llvm::InsertElementInst>(insertBase);
if (ie == NULL) {
if (llvm::isa<llvm::UndefValue>(insertBase))
return;
llvm::ConstantVector *cv =
llvm::dyn_cast<llvm::ConstantVector>(insertBase);
Assert(cv != NULL);
Assert(iOffset < (int)cv->getNumOperands());
elements[iOffset] = cv->getOperand(iOffset);
}
}
}
/** Tests to see if all of the elements of the vector in the 'v' parameter
are equal. Like lValuesAreEqual(), this is a conservative test and may
return false for arrays where the values are actually all equal. */
bool
LLVMVectorValuesAllEqual(llvm::Value *v, int vectorLength,
std::vector<llvm::PHINode *> &seenPhis) {
if (llvm::isa<llvm::ConstantAggregateZero>(v))
return true;
llvm::ConstantVector *cv = llvm::dyn_cast<llvm::ConstantVector>(v);
if (cv != NULL)
return (cv->getSplatValue() != NULL);
llvm::BinaryOperator *bop = llvm::dyn_cast<llvm::BinaryOperator>(v);
if (bop != NULL)
return (LLVMVectorValuesAllEqual(bop->getOperand(0), vectorLength,
seenPhis) &&
LLVMVectorValuesAllEqual(bop->getOperand(1), vectorLength,
seenPhis));
llvm::CastInst *cast = llvm::dyn_cast<llvm::CastInst>(v);
if (cast != NULL)
return LLVMVectorValuesAllEqual(cast->getOperand(0), vectorLength,
seenPhis);
llvm::InsertElementInst *ie = llvm::dyn_cast<llvm::InsertElementInst>(v);
if (ie != NULL) {
llvm::Value *elements[ISPC_MAX_NVEC];
LLVMFlattenInsertChain(ie, vectorLength, elements);
// We will ignore any values of elements[] that are NULL; as they
// correspond to undefined values--we just want to see if all of
// the defined values have the same value.
int lastNonNull = 0;
while (lastNonNull < vectorLength && elements[lastNonNull] == NULL)
++lastNonNull;
if (lastNonNull == vectorLength)
// all of them are undef!
return true;
for (int i = lastNonNull; i < vectorLength; ++i) {
if (elements[i] == NULL)
continue;
std::vector<llvm::PHINode *> seenPhi0;
std::vector<llvm::PHINode *> seenPhi1;
if (lValuesAreEqual(elements[lastNonNull], elements[i], seenPhi0,
seenPhi1) == false)
return false;
lastNonNull = i;
}
return true;
}
llvm::PHINode *phi = llvm::dyn_cast<llvm::PHINode>(v);
if (phi) {
for (unsigned int i = 0; i < seenPhis.size(); ++i)
if (seenPhis[i] == phi)
return true;
seenPhis.push_back(phi);
unsigned int numIncoming = phi->getNumIncomingValues();
// Check all of the incoming values: if all of them are all equal,
// then we're good.
for (unsigned int i = 0; i < numIncoming; ++i) {
if (!LLVMVectorValuesAllEqual(phi->getIncomingValue(i), vectorLength,
seenPhis)) {
seenPhis.pop_back();
return false;
}
}
seenPhis.pop_back();
return true;
}
Assert(!llvm::isa<llvm::Constant>(v));
if (llvm::isa<llvm::CallInst>(v) || llvm::isa<llvm::LoadInst>(v) ||
!llvm::isa<llvm::Instruction>(v))
return false;
llvm::ShuffleVectorInst *shuffle = llvm::dyn_cast<llvm::ShuffleVectorInst>(v);
if (shuffle != NULL) {
llvm::Value *indices = shuffle->getOperand(2);
if (LLVMVectorValuesAllEqual(indices, vectorLength, seenPhis))
// The easy case--just a smear of the same element across the
// whole vector.
return true;
// TODO: handle more general cases?
return false;
}
#if 0
fprintf(stderr, "all equal: ");
v->dump();
fprintf(stderr, "\n");
llvm::Instruction *inst = llvm::dyn_cast<llvm::Instruction>(v);
if (inst) {
inst->getParent()->dump();
fprintf(stderr, "\n");
fprintf(stderr, "\n");
}
#endif
return false;
}