[llvm] [LICM] Fold associative binary ops to promote code hoisting (PR #81608)
Ricardo Jesus via llvm-commits
llvm-commits at lists.llvm.org
Tue Jul 23 03:52:00 PDT 2024
================
@@ -2779,6 +2781,60 @@ static bool hoistMulAddAssociation(Instruction &I, Loop &L,
return true;
}
+/// Reassociate general associative binary expressions of the form
+///
+/// 1. "(LV op C1) op C2" ==> "LV op (C1 op C2)"
+///
+/// where op is an associative binary op, LV is a loop variant, and C1 and C2
+/// are loop invariants that we want to hoist.
+///
+/// TODO: This can be extended to more cases such as
+/// 2. "C1 op (C2 op LV)" ==> "(C1 op C2) op LV"
+/// 3. "(C1 op LV) op C2" ==> "LV op (C1 op C2)" if op is commutative
+/// 4. "C1 op (LV op C2)" ==> "(C1 op C2) op LV" if op is commutative
+static bool hoistBOAssociation(Instruction &I, Loop &L,
+ ICFLoopSafetyInfo &SafetyInfo,
+ MemorySSAUpdater &MSSAU, AssumptionCache *AC,
+ DominatorTree *DT) {
+ BinaryOperator *BO = dyn_cast<BinaryOperator>(&I);
+ if (!BO || !BO->isAssociative())
+ return false;
+
+ Instruction::BinaryOps Opcode = BO->getOpcode();
+ BinaryOperator *Op0 = dyn_cast<BinaryOperator>(BO->getOperand(0));
+
+ // Transform: "(LV op C1) op C2" ==> "LV op (C1 op C2)"
+ if (Op0 && Op0->getOpcode() == Opcode) {
+ Value *LV = Op0->getOperand(0);
+ Value *C1 = Op0->getOperand(1);
+ Value *C2 = BO->getOperand(1);
+
+ if (L.isLoopInvariant(LV) || !L.isLoopInvariant(C1) ||
+ !L.isLoopInvariant(C2))
+ return false;
+
+ auto *Preheader = L.getLoopPreheader();
+ assert(Preheader && "Loop is not in simplify form?");
+ IRBuilder<> Builder(Preheader->getTerminator());
+ Value *Inv = Builder.CreateBinOp(Opcode, C1, C2, "invariant.op");
+
+ auto *NewBO =
+ BinaryOperator::Create(Opcode, LV, Inv, BO->getName() + ".reass", BO);
+ NewBO->copyIRFlags(BO);
----------------
rj-jesus wrote:
Thanks for catching this, I'll fix this and increase the test coverage.
https://github.com/llvm/llvm-project/pull/81608
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