[Attributor] Ignore uses if a value is simplified
If we have a replacement for a value, via AAValueSimplify, the original
value will lose all its uses. Thus, as long as a value is simplified we
can skip the uses in checkForAllUses, given that these uses are
transitive uses for the simplified version and will therefore affect the
simplified version as necessary.
Since this allowed us to remove calls without side-effects and a known
return value, we need to make sure not to eliminate `musttail` calls.
Those we keep around, or later remove the entire `musttail` call chain.
diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 1d0e82c..d53e8e4 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -2916,6 +2916,12 @@
if (V.use_empty())
return ChangeStatus::UNCHANGED;
+ bool UsedAssumedInformation = false;
+ Optional<ConstantInt *> CI =
+ getAssumedConstant(A, V, *this, UsedAssumedInformation);
+ if (CI.hasValue() && CI.getValue())
+ return ChangeStatus::UNCHANGED;
+
UndefValue &UV = *UndefValue::get(V.getType());
bool AnyChange = A.changeValueAfterManifest(V, UV);
return AnyChange ? ChangeStatus::CHANGED : ChangeStatus::UNCHANGED;
@@ -3092,6 +3098,9 @@
UndefValue &UV = *UndefValue::get(getAssociatedFunction()->getReturnType());
auto RetInstPred = [&](Instruction &I) {
ReturnInst &RI = cast<ReturnInst>(I);
+ if (auto *CI = dyn_cast<CallInst>(RI.getReturnValue()))
+ if (CI->isMustTailCall())
+ return true;
if (!isa<UndefValue>(RI.getReturnValue()))
AnyChange |= A.changeUseAfterManifest(RI.getOperandUse(0), UV);
return true;
@@ -4730,6 +4739,14 @@
AAValueSimplifyCallSiteReturned(const IRPosition &IRP)
: AAValueSimplifyReturned(IRP) {}
+ /// See AbstractAttribute::manifest(...).
+ ChangeStatus manifest(Attributor &A) override {
+ if (auto *CI = dyn_cast<CallInst>(&getAssociatedValue()))
+ if (CI->isMustTailCall())
+ return ChangeStatus::UNCHANGED;
+ return AAValueSimplifyReturned::manifest(A);
+ }
+
void trackStatistics() const override {
STATS_DECLTRACK_CSRET_ATTR(value_simplify)
}
@@ -6557,6 +6574,24 @@
bool Attributor::checkForAllUses(
const function_ref<bool(const Use &, bool &)> &Pred,
const AbstractAttribute &QueryingAA, const Value &V) {
+
+ // Check the trivial case first as it catches void values.
+ if (V.use_empty())
+ return true;
+
+ // If the value is replaced by another one, for now a constant, we do not have
+ // uses. Note that this requires users of `checkForAllUses` to not recurse but
+ // instead use the `follow` callback argument to look at transitive users,
+ // however, that should be clear from the presence of the argument.
+ bool UsedAssumedInformation = false;
+ Optional<ConstantInt *> CI =
+ getAssumedConstant(*this, V, QueryingAA, UsedAssumedInformation);
+ if (CI.hasValue() && CI.getValue()) {
+ LLVM_DEBUG(dbgs() << "[Attributor] Value is simplified, uses skipped: " << V
+ << " -> " << *CI.getValue() << "\n");
+ return true;
+ }
+
const IRPosition &IRP = QueryingAA.getIRPosition();
SmallVector<const Use *, 16> Worklist;
SmallPtrSet<const Use *, 16> Visited;
@@ -6567,9 +6602,6 @@
LLVM_DEBUG(dbgs() << "[Attributor] Got " << Worklist.size()
<< " initial uses to check\n");
- if (Worklist.empty())
- return true;
-
bool AnyDead = false;
const Function *ScopeFn = IRP.getAnchorScope();
const auto *LivenessAA =