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Implement a fixme. The helps loops that have induction variables of different

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types in them.  Instead of creating an induction variable for all types, it
creates a single induction variable and casts to the other sizes.  This generates
this code:

no_exit:                ; preds = %entry, %no_exit
        %indvar = phi uint [ %indvar.next, %no_exit ], [ 0, %entry ]            ; <uint> [#uses=4]
***     %j.0.0 = cast uint %indvar to short             ; <short> [#uses=1]
        %indvar = cast uint %indvar to int              ; <int> [#uses=1]
        %tmp.7 = getelementptr short* %P, uint %indvar          ; <short*> [#uses=1]
        store short %j.0.0, short* %tmp.7
        %inc.0 = add int %indvar, 1             ; <int> [#uses=2]
        %tmp.2 = setlt int %inc.0, %N           ; <bool> [#uses=1]
        %indvar.next = add uint %indvar, 1              ; <uint> [#uses=1]
        br bool %tmp.2, label %no_exit, label %loopexit

instead of:

no_exit:                ; preds = %entry, %no_exit
        %indvar = phi ushort [ %indvar.next, %no_exit ], [ 0, %entry ]          ; <ushort> [#uses=2]
***     %indvar = phi uint [ %indvar.next, %no_exit ], [ 0, %entry ]            ; <uint> [#uses=3]
        %indvar = cast uint %indvar to int              ; <int> [#uses=1]
        %indvar = cast ushort %indvar to short          ; <short> [#uses=1]
        %tmp.7 = getelementptr short* %P, uint %indvar          ; <short*> [#uses=1]
        store short %indvar, short* %tmp.7
        %inc.0 = add int %indvar, 1             ; <int> [#uses=2]
        %tmp.2 = setlt int %inc.0, %N           ; <bool> [#uses=1]
        %indvar.next = add uint %indvar, 1
***     %indvar.next = add ushort %indvar, 1
        br bool %tmp.2, label %no_exit, label %loopexit

This is an improvement in register pressure, but probably doesn't happen that
often.

The more important fix will be to get rid of the redundant add.

llvm-svn: 13101
This commit is contained in:
Chris Lattner 2004-04-21 22:22:01 +00:00
parent 7d02bae5d8
commit a3e2004609
1 changed files with 20 additions and 17 deletions
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37
lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -390,10 +390,8 @@ void IndVarSimplify::runOnLoop(Loop *L) {
// Compute the type of the largest recurrence expression.
//
const Type *LargestType = IndVars[0].first->getType();
bool DifferingSizes = false;
for (unsigned i = 1, e = IndVars.size(); i != e; ++i) {
const Type *Ty = IndVars[i].first->getType();
DifferingSizes |= Ty->getPrimitiveSize() != LargestType->getPrimitiveSize();
if (Ty->getPrimitiveSize() > LargestType->getPrimitiveSize())
LargestType = Ty;
}
@ -411,30 +409,35 @@ void IndVarSimplify::runOnLoop(Loop *L) {
if (!isa<SCEVCouldNotCompute>(IterationCount))
LinearFunctionTestReplace(L, IterationCount, Rewriter);
#if 0
// If there were induction variables of other sizes, cast the primary
// induction variable to the right size for them, avoiding the need for the
// code evaluation methods to insert induction variables of different sizes.
// FIXME!
if (DifferingSizes) {
std::map<unsigned, Value*> InsertedSizes;
for (unsigned i = 0, e = IndVars.size(); i != e; ++i) {
}
}
#endif
// Now that we have a canonical induction variable, we can rewrite any
// recurrences in terms of the induction variable. Start with the auxillary
// induction variables, and recursively rewrite any of their uses.
BasicBlock::iterator InsertPt = Header->begin();
while (isa<PHINode>(InsertPt)) ++InsertPt;
// If there were induction variables of other sizes, cast the primary
// induction variable to the right size for them, avoiding the need for the
// code evaluation methods to insert induction variables of different sizes.
std::map<unsigned, Value*> InsertedSizes;
InsertedSizes[LargestType->getPrimitiveSize()] = IndVar;
while (!IndVars.empty()) {
PHINode *PN = IndVars.back().first;
Value *NewVal = Rewriter.ExpandCodeFor(IndVars.back().second, InsertPt,
PN->getType());
const Type *Ty = PN->getType()->getUnsignedVersion();
Value *&IV = InsertedSizes[Ty->getPrimitiveSize()];
if (IV == 0) {
// Insert a new cast instruction, which will hold this recurrence.
std::string Name = PN->getName();
PN->setName("");
IV = new CastInst(IndVar, Ty, Name, InsertPt);
}
Value *V = IV;
if (PN->getType() != Ty)
V = new CastInst(V, PN->getType(), V->getName(), InsertPt);
// Replace the old PHI Node with the inserted computation.
PN->replaceAllUsesWith(NewVal);
PN->replaceAllUsesWith(V);
DeadInsts.insert(PN);
IndVars.pop_back();
++NumRemoved;