LICM: handle BinOp in RHS correctly

Author: artagnon

llvm/lib/Transforms/Scalar/LICM.cpp

@@ -2824,15 +2824,15 @@ static bool hoistBOAssociation(Instruction &I, Loop &L,
   if (Opcode != Instruction::Add && Opcode != Instruction::Mul)
     return false;
 
-  bool BinOpInRHS = isa<BinaryOperator>(BO->getOperand(1));
-  auto *BO0 = dyn_cast<BinaryOperator>(BO->getOperand(BinOpInRHS));
+  bool LVInRHS = L.isLoopInvariant(BO->getOperand(0));
+  auto *BO0 = dyn_cast<BinaryOperator>(BO->getOperand(LVInRHS));
   if (!BO0 || BO0->getOpcode() != Opcode || !BO0->isAssociative() ||
       BO0->hasNUsesOrMore(3))
     return false;
 
   Value *LV = BO0->getOperand(0);
   Value *C1 = BO0->getOperand(1);
-  Value *C2 = BO->getOperand(!BinOpInRHS);
+  Value *C2 = BO->getOperand(!LVInRHS);
 
   assert(BO->isCommutative() && BO0->isCommutative() &&
          "Associativity implies commutativity");

llvm/test/Transforms/LICM/hoist-binop.ll

@@ -142,6 +142,33 @@ loop:
   br label %loop
 }
 
+; Hoist ADD and copy NUW if both ops have it.
+; A version where the LHS and RHS of the outer BinOp are BinOps.
+define void @add_nuw_twobinops(i64 %c1, i64 %c2) {
+; CHECK-LABEL: @add_nuw_twobinops(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[C2_PLUS_2:%.*]] = add nuw i64 [[C2:%.*]], 2
+; CHECK-NEXT:    [[INVARIANT_OP:%.*]] = add nuw i64 [[C1:%.*]], [[C2_PLUS_2]]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT_REASS:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[STEP_ADD:%.*]] = add nuw i64 [[C1]], [[INDEX]]
+; CHECK-NEXT:    call void @use(i64 [[STEP_ADD]])
+; CHECK-NEXT:    [[INDEX_NEXT_REASS]] = add nuw i64 [[INDEX]], [[INVARIANT_OP]]
+; CHECK-NEXT:    br label [[LOOP]]
+;
+entry:
+  br label %loop
+
+loop:
+  %index = phi i64 [ 0, %entry ], [ %index.next, %loop ]
+  %step.add = add nuw i64 %c1, %index
+  call void @use(i64 %step.add)
+  %c2.plus.2 = add nuw i64 %c2, 2
+  %index.next = add nuw i64 %step.add, %c2.plus.2
+  br label %loop
+}
+
 ; Hoist MUL and drop NUW even if both ops have it.
 define void @mul_nuw(i64 %c1, i64 %c2) {
 ; CHECK-LABEL: @mul_nuw(
@@ -241,6 +268,33 @@ loop:
   br label %loop
 }
 
+; Hoist MUL and drop NUW even if both ops have it.
+; A version where the LHS and RHS of the outer BinOp are BinOps.
+define void @mul_nuw_twobinops(i64 %c1, i64 %c2) {
+; CHECK-LABEL: @mul_nuw_twobinops(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[C2_PLUS_2:%.*]] = add nuw i64 [[C2:%.*]], 2
+; CHECK-NEXT:    [[INVARIANT_OP:%.*]] = mul i64 [[C1:%.*]], [[C2_PLUS_2]]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDEX_NEXT_REASS:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[STEP_ADD:%.*]] = mul nuw i64 [[C1]], [[INDEX]]
+; CHECK-NEXT:    call void @use(i64 [[STEP_ADD]])
+; CHECK-NEXT:    [[INDEX_NEXT_REASS]] = mul i64 [[INDEX]], [[INVARIANT_OP]]
+; CHECK-NEXT:    br label [[LOOP]]
+;
+entry:
+  br label %loop
+
+loop:
+  %index = phi i64 [ 0, %entry ], [ %index.next, %loop ]
+  %step.add = mul nuw i64 %c1, %index
+  call void @use(i64 %step.add)
+  %c2.plus.2 = add nuw i64 %c2, 2
+  %index.next = mul nuw i64 %step.add, %c2.plus.2
+  br label %loop
+}
+
 ; Hoist ADD but don't copy NUW if only one op has it.
 define void @add_no_nuw(i64 %c1, i64 %c2) {
 ; CHECK-LABEL: @add_no_nuw(