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Semantically revert 151015. Add a comment on why we should be able to assert

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the dominance once the dominates method is fixed and why we can use the builder's
insertion point.
Fixes pr12048.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151125 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2012-02-22 03:21:39 +00:00
parent 57708abb10
commit 919a503458
2 changed files with 55 additions and 7 deletions
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24
lib/Analysis/ScalarEvolutionExpander.cpp
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@@ -31,11 +31,20 @@ using namespace llvm;
Value *SCEVExpander::ReuseOrCreateCast(Value *V, Type *Ty,
Instruction::CastOps Op,
BasicBlock::iterator IP) {
// All new or reused instructions must strictly dominate their uses.
// It would be nice to assert this here, but we don't always know where
// the next instructions will be added as the caller can move the
// Builder's InsertPt before creating them and we might be called with
// an invalid InsertPt.
// This function must be called with the builder having a valid insertion
// point. It doesn't need to be the actual IP where the uses of the returned
// cast will be added, but it must dominate such IP.
// We use this precondition to assert that we can produce a cast that will
// dominate all its uses. In particular, this is crussial for the case
// where the builder's insertion point *is* the point where we were asked
// to put the cast.
// Since we don't know the the builder's insertion point is actually
// where the uses will be added (only that it dominates it), we are
// not allowed to move it.
BasicBlock::iterator BIP = Builder.GetInsertPoint();
// FIXME: enable once our implementation of dominates is fixed.
// assert(BIP == IP || SE.DT->dominates(IP, BIP));
// Check to see if there is already a cast!
for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
@@ -44,8 +53,9 @@ Value *SCEVExpander::ReuseOrCreateCast(Value *V, Type *Ty,
if (U->getType() == Ty)
if (CastInst *CI = dyn_cast<CastInst>(U))
if (CI->getOpcode() == Op) {
// If the cast isn't where we want it, fix it.
if (BasicBlock::iterator(CI) != IP) {
// If the cast isn't where we want it or if it doesn't dominate
// a use in BIP, fix it.
if (BasicBlock::iterator(CI) != IP || BIP == IP) {
// Create a new cast, and leave the old cast in place in case
// it is being used as an insert point. Clear its operand
// so that it doesn't hold anything live.