[LVI] Add select handling
Teach LVI to handle select instructions in the exact same way it handles PHI nodes. This is useful since various parts of the optimizer convert PHI nodes into selects and we don't want these transformations to cause inferior optimization.
Note that this patch does nothing to exploit the implied constraint on the inputs represented by the select condition itself. That will be a later patch and is blocked on http://reviews.llvm.org/D14476
llvm-svn: 259429
diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 0d1d34e..cdeaaa3 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -389,6 +389,8 @@
Value *Val, BasicBlock *BB);
bool solveBlockValuePHINode(LVILatticeVal &BBLV,
PHINode *PN, BasicBlock *BB);
+ bool solveBlockValueSelect(LVILatticeVal &BBLV,
+ SelectInst *S, BasicBlock *BB);
bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI, BasicBlock *BB);
void mergeAssumeBlockValueConstantRange(Value *Val, LVILatticeVal &BBLV,
@@ -587,6 +589,13 @@
return true;
}
+ if (auto *SI = dyn_cast<SelectInst>(BBI)) {
+ if (!solveBlockValueSelect(Res, SI, BB))
+ return false;
+ insertResult(Val, BB, Res);
+ return true;
+ }
+
// If this value is a nonnull pointer, record it's range and bailout.
PointerType *PT = dyn_cast<PointerType>(BBI->getType());
if (PT && isKnownNonNull(BBI)) {
@@ -809,6 +818,46 @@
}
}
+bool LazyValueInfoCache::solveBlockValueSelect(LVILatticeVal &BBLV,
+ SelectInst *SI, BasicBlock *BB) {
+
+ // Recurse on our inputs if needed
+ if (!hasBlockValue(SI->getTrueValue(), BB)) {
+ if (pushBlockValue(std::make_pair(BB, SI->getTrueValue())))
+ return false;
+ BBLV.markOverdefined();
+ return true;
+ }
+ LVILatticeVal TrueVal = getBlockValue(SI->getTrueValue(), BB);
+ // If we hit overdefined, don't ask more queries. We want to avoid poisoning
+ // extra slots in the table if we can.
+ if (TrueVal.isOverdefined()) {
+ BBLV.markOverdefined();
+ return true;
+ }
+
+ if (!hasBlockValue(SI->getFalseValue(), BB)) {
+ if (pushBlockValue(std::make_pair(BB, SI->getFalseValue())))
+ return false;
+ BBLV.markOverdefined();
+ return true;
+ }
+ LVILatticeVal FalseVal = getBlockValue(SI->getFalseValue(), BB);
+ // If we hit overdefined, don't ask more queries. We want to avoid poisoning
+ // extra slots in the table if we can.
+ if (FalseVal.isOverdefined()) {
+ BBLV.markOverdefined();
+ return true;
+ }
+
+ LVILatticeVal Result; // Start Undefined.
+ Result.mergeIn(TrueVal, DL);
+ Result.mergeIn(FalseVal, DL);
+ assert(!Result.isOverdefined() && "Should have exited previously");
+ BBLV = Result;
+ return true;
+}
+
bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI,
BasicBlock *BB) {