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[BasicAA] Move experimental.guard modelling to getModRefBehavior() 

While we can't express this with attributes yet, we can model
these intrinsics as readonly + writing inaccessible memory (for
the control dependence) in FMRB. This way we don't need to
special-case them in getModRefInfo(), it falls out of the usual
logic.
This commit is contained in:
Nikita Popov 2022-09-14 17:10:39 +02:00
parent 8df376db72
commit 60990d9042
1 changed files with 9 additions and 13 deletions
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22
llvm/lib/Analysis/BasicAliasAnalysis.cpp
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@ -790,6 +790,15 @@ FunctionModRefBehavior BasicAAResult::getModRefBehavior(const Function *F) {
if (F->doesNotAccessMemory())
return FunctionModRefBehavior::none();
switch (F->getIntrinsicID()) {
case Intrinsic::experimental_guard:
case Intrinsic::experimental_deoptimize:
// These intrinsics can read arbitrary memory, and additionally modref
// inaccessible memory to model control dependence.
return FunctionModRefBehavior::readOnly() |
FunctionModRefBehavior::inaccessibleMemOnly(ModRefInfo::ModRef);
}
// If the function declares it only reads memory, go with that.
ModRefInfo MR = ModRefInfo::ModRef;
if (F->onlyReadsMemory())
@ -980,19 +989,6 @@ ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call,
return ModRefInfo::NoModRef;
}
// Guard intrinsics are marked as arbitrarily writing so that proper control
// dependencies are maintained but they never mods any particular memory
// location.
//
// *Unlike* assumes, guard intrinsics are modeled as reading memory since the
// heap state at the point the guard is issued needs to be consistent in case
// the guard invokes the "deopt" continuation.
if (isIntrinsicCall(Call, Intrinsic::experimental_guard))
return ModRefInfo::Ref;
// The same applies to deoptimize which is essentially a guard(false).
if (isIntrinsicCall(Call, Intrinsic::experimental_deoptimize))
return ModRefInfo::Ref;
// Like assumes, invariant.start intrinsics were also marked as arbitrarily
// writing so that proper control dependencies are maintained but they never
// mod any particular memory location visible to the IR.