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authordim <dim@FreeBSD.org>2012-08-15 19:34:23 +0000
committerdim <dim@FreeBSD.org>2012-08-15 19:34:23 +0000
commit721c201bd55ffb73cb2ba8d39e0570fa38c44e15 (patch)
treeeacfc83d988e4b9d11114387ae7dc41243f2a363 /lib/Transforms/Scalar/IndVarSimplify.cpp
parent2b2816e083a455f7a656ae88b0fd059d1688bb36 (diff)
downloadFreeBSD-src-721c201bd55ffb73cb2ba8d39e0570fa38c44e15.zip
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Vendor import of llvm trunk r161861:
http://llvm.org/svn/llvm-project/llvm/trunk@161861
Diffstat (limited to 'lib/Transforms/Scalar/IndVarSimplify.cpp')
-rw-r--r--lib/Transforms/Scalar/IndVarSimplify.cpp74
1 files changed, 68 insertions, 6 deletions
diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index a9ba657..37f8bdf 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1215,21 +1215,26 @@ static PHINode *getLoopPhiForCounter(Value *IncV, Loop *L, DominatorTree *DT) {
return 0;
}
-/// needsLFTR - LinearFunctionTestReplace policy. Return true unless we can show
-/// that the current exit test is already sufficiently canonical.
-static bool needsLFTR(Loop *L, DominatorTree *DT) {
+/// Return the compare guarding the loop latch, or NULL for unrecognized tests.
+static ICmpInst *getLoopTest(Loop *L) {
assert(L->getExitingBlock() && "expected loop exit");
BasicBlock *LatchBlock = L->getLoopLatch();
// Don't bother with LFTR if the loop is not properly simplified.
if (!LatchBlock)
- return false;
+ return 0;
BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
assert(BI && "expected exit branch");
+ return dyn_cast<ICmpInst>(BI->getCondition());
+}
+
+/// needsLFTR - LinearFunctionTestReplace policy. Return true unless we can show
+/// that the current exit test is already sufficiently canonical.
+static bool needsLFTR(Loop *L, DominatorTree *DT) {
// Do LFTR to simplify the exit condition to an ICMP.
- ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
+ ICmpInst *Cond = getLoopTest(L);
if (!Cond)
return true;
@@ -1259,6 +1264,48 @@ static bool needsLFTR(Loop *L, DominatorTree *DT) {
return Phi != getLoopPhiForCounter(IncV, L, DT);
}
+/// Recursive helper for hasConcreteDef(). Unfortunately, this currently boils
+/// down to checking that all operands are constant and listing instructions
+/// that may hide undef.
+static bool hasConcreteDefImpl(Value *V, SmallPtrSet<Value*, 8> &Visited,
+ unsigned Depth) {
+ if (isa<Constant>(V))
+ return !isa<UndefValue>(V);
+
+ if (Depth >= 6)
+ return false;
+
+ // Conservatively handle non-constant non-instructions. For example, Arguments
+ // may be undef.
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (!I)
+ return false;
+
+ // Load and return values may be undef.
+ if(I->mayReadFromMemory() || isa<CallInst>(I) || isa<InvokeInst>(I))
+ return false;
+
+ // Optimistically handle other instructions.
+ for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) {
+ if (!Visited.insert(*OI))
+ continue;
+ if (!hasConcreteDefImpl(*OI, Visited, Depth+1))
+ return false;
+ }
+ return true;
+}
+
+/// Return true if the given value is concrete. We must prove that undef can
+/// never reach it.
+///
+/// TODO: If we decide that this is a good approach to checking for undef, we
+/// may factor it into a common location.
+static bool hasConcreteDef(Value *V) {
+ SmallPtrSet<Value*, 8> Visited;
+ Visited.insert(V);
+ return hasConcreteDefImpl(V, Visited, 0);
+}
+
/// AlmostDeadIV - Return true if this IV has any uses other than the (soon to
/// be rewritten) loop exit test.
static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) {
@@ -1283,6 +1330,8 @@ static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) {
/// valid count without scaling the address stride, so it remains a pointer
/// expression as far as SCEV is concerned.
///
+/// Currently only valid for LFTR. See the comments on hasConcreteDef below.
+///
/// FIXME: Accept -1 stride and set IVLimit = IVInit - BECount
///
/// FIXME: Accept non-unit stride as long as SCEV can reduce BECount * Stride.
@@ -1331,6 +1380,19 @@ FindLoopCounter(Loop *L, const SCEV *BECount,
if (getLoopPhiForCounter(IncV, L, DT) != Phi)
continue;
+ // Avoid reusing a potentially undef value to compute other values that may
+ // have originally had a concrete definition.
+ if (!hasConcreteDef(Phi)) {
+ // We explicitly allow unknown phis as long as they are already used by
+ // the loop test. In this case we assume that performing LFTR could not
+ // increase the number of undef users.
+ if (ICmpInst *Cond = getLoopTest(L)) {
+ if (Phi != getLoopPhiForCounter(Cond->getOperand(0), L, DT)
+ && Phi != getLoopPhiForCounter(Cond->getOperand(1), L, DT)) {
+ continue;
+ }
+ }
+ }
const SCEV *Init = AR->getStart();
if (BestPhi && !AlmostDeadIV(BestPhi, LatchBlock, Cond)) {
@@ -1347,7 +1409,7 @@ FindLoopCounter(Loop *L, const SCEV *BECount,
// If two IVs both count from zero or both count from nonzero then the
// narrower is likely a dead phi that has been widened. Use the wider phi
// to allow the other to be eliminated.
- if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType()))
+ else if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType()))
continue;
}
BestPhi = Phi;
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