Simplify the side effect stuff a bit more and make licm/sinking
both work right according to the new flags.
This removes the TII::isReallySideEffectFree predicate, and adds
TII::isInvariantLoad.
It removes NeverHasSideEffects+MayHaveSideEffects and adds
UnmodeledSideEffects as machine instr flags. Now the clients
can decide everything they need.
I think isRematerializable can be implemented in terms of the
flags we have now, though I will let others tackle that.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45843 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineLICM.cpp b/lib/CodeGen/MachineLICM.cpp
index 04211ab..92256eb 100644
--- a/lib/CodeGen/MachineLICM.cpp
+++ b/lib/CodeGen/MachineLICM.cpp
@@ -223,6 +223,26 @@
/// effects that aren't captured by the operands or other flags.
///
bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
+ const TargetInstrDesc &TID = I.getDesc();
+
+ // Ignore stuff that we obviously can't hoist.
+ if (TID.mayStore() || TID.isCall() || TID.isReturn() || TID.isBranch() ||
+ TID.hasUnmodeledSideEffects())
+ return false;
+
+ if (TID.mayLoad()) {
+ // Okay, this instruction does a load. As a refinement, allow the target
+ // to decide whether the loaded value is actually a constant. If so, we
+ // can actually use it as a load.
+ if (!TII->isInvariantLoad(&I)) {
+ // FIXME: we should be able to sink loads with no other side effects if
+ // there is nothing that can change memory from here until the end of
+ // block. This is a trivial form of alias analysis.
+ return false;
+ }
+ }
+
+
DEBUG({
DOUT << "--- Checking if we can hoist " << I;
if (I.getDesc().getImplicitUses()) {
@@ -243,8 +263,8 @@
DOUT << " -> " << MRI->getName(*ImpDefs) << "\n";
}
- if (TII->hasUnmodelledSideEffects(&I))
- DOUT << " * Instruction has side effects.\n";
+ //if (TII->hasUnmodelledSideEffects(&I))
+ //DOUT << " * Instruction has side effects.\n";
});
// The instruction is loop invariant if all of its operands are loop-invariant
@@ -268,9 +288,6 @@
return false;
}
- // Don't hoist something that has unmodelled side effects.
- if (TII->hasUnmodelledSideEffects(&I)) return false;
-
// If we got this far, the instruction is loop invariant!
return true;
}