[DAPHNE-#911] Correct reference counter for arith.select result.

- The MLIR operation arith.select is frequently created during the canonicalization of scf.if (which, in turn, is created by DaphneDSL if-statements).
- arith.select takes a boolean argument (condition) plus two additional arguments, one of which it selects/returns based on the value of the condition.
- arith.select needs to be taken into account in DAPHNE's object reference counter management, because:
  - We decrease the reference counter of SSA values after their last use as operands (the arith.select could be the last user).
  - We have no clue which of the two last operands of arith.select is returned at run-time.
  - However, the return value is the same runtime object as one of the two latter operands.
  - To ensure the correct reference counter for the result after the arith.select, we need to increase the counter of the result before we decrease the counters of the operands.
- We had already implemented this fix, but applied it only for string operands/results.
- However, we must apply the fix for all operand/result types that have a reference counter at run-time.
- Fixed ManageObjRefPass.
- Added several script-level test cases testing the behavior for matrices, frames, lists, and strings and different settings of the if-then-else in DaphneDSL.

src/compiler/lowering/ManageObjRefsPass.cpp

@@ -72,7 +72,8 @@ void processValue(OpBuilder builder, Value v) {
     // TODO Address handles from the distributed runtime (but they will be
     // removed soon anyway).
     // We only need to manage the reference counters of DAPHNE data objects
-    // like matrices and frames (not of scalars).
+    // (like matrices, frames, and lists), but not for scalars (except for
+    // strings) and other types.
 
     Operation *defOp = v.getDefiningOp();
     if (defOp && llvm::isa<daphne::ConvertDenseMatrixToMemRef>(defOp))
@@ -96,12 +97,16 @@ void processValue(OpBuilder builder, Value v) {
         builder.create<daphne::IncRefOp>(v.getLoc(), v);
     }
 
-    // Increase the reference counter of the result of the arith.select op, if
-    // it is a string scalar. This is necessary because for arith.select, we
-    // have no clue which of its two arguments (2nd or 3rd one) it will return.
+    // Increase the reference counter of the result of an arith.select op,
+    // if the result is of a type that has a reference counter at runtime.
+    // This is necessary because for arith.select, we have no clue which of
+    // its two arguments (2nd or 3rd one) it will return.
     // Unless we do something about it, the reference counter of the result will
     // be too low by 1. Thus, we increase the result's reference counter here.
-    if (defOp && llvm::isa<arith::SelectOp>(defOp) && llvm::isa<daphne::StringType>(v.getType())) {
+    // TODO This might cause a memory leak, if this arith.select is not the last
+    // user of both input SSA values (further investigation necessary).
+    if (defOp && llvm::isa<arith::SelectOp>(defOp) &&
+        llvm::isa<daphne::MatrixType, daphne::FrameType, daphne::ListType, daphne::StringType>(v.getType())) {
         builder.setInsertionPointAfter(defOp);
         builder.create<daphne::IncRefOp>(v.getLoc(), v);
     }

test/api/cli/controlflow/ControlFlowTest.cpp

@@ -49,7 +49,7 @@ const std::string dirPath = "test/api/cli/controlflow/";
         }                                                                                                              \
     }
 
-MAKE_TEST_CASE("if", 8)
+MAKE_TEST_CASE("if", 20)
 MAKE_TEST_CASE("for", 23)
 MAKE_TEST_CASE("while", 17)
 MAKE_TEST_CASE("nested", 26)

test/api/cli/controlflow/if_10.daphne

@@ -0,0 +1,12 @@
+// Update a matrix inside else-branch of if-statement with value computed outside if-statement (scf.if gets rewritten to arith.select).
+X = [0];
+Y = X + 1;
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    r = 99; # do something unrelated to X
+else
+    X = Y;
+print(r);
+print(X);

test/api/cli/controlflow/if_10.txt

@@ -0,0 +1,3 @@
+99
+DenseMatrix(1x1, int64_t)
+0

test/api/cli/controlflow/if_11.daphne

@@ -0,0 +1,12 @@
+// Update a matrix inside then-branch and else-branch of if-statement with values computed outside if-statement (scf.if gets rewritten to arith.select).
+X = [0];
+Y = X + 1;
+Z = X + 2;
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    X = Y;
+else
+    X = Z;
+print(X);

test/api/cli/controlflow/if_11.txt

@@ -0,0 +1,2 @@
+DenseMatrix(1x1, int64_t)
+1

test/api/cli/controlflow/if_12.daphne

@@ -0,0 +1,9 @@
+// Update a frame inside then-branch of if-statement with value computed outside if-statement (scf.if gets rewritten to arith.select).
+X = {"a": [0]};
+Y = rbind(X, X);
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    X = Y;
+print(X);

test/api/cli/controlflow/if_12.txt

@@ -0,0 +1,3 @@
+Frame(2x1, [a:int64_t])
+0
+0

test/api/cli/controlflow/if_13.daphne

@@ -0,0 +1,12 @@
+// Update a frame inside else-branch of if-statement with value computed outside if-statement (scf.if gets rewritten to arith.select).
+X = {"a": [0]};
+Y = rbind(X, X);
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    r = 99; # do something unrelated to X
+else
+    X = Y;
+print(r);
+print(X);

test/api/cli/controlflow/if_13.txt

@@ -0,0 +1,3 @@
+99
+Frame(1x1, [a:int64_t])
+0

test/api/cli/controlflow/if_14.daphne

@@ -0,0 +1,12 @@
+// Update a frame inside then-branch and else-branch of if-statement with values computed outside if-statement (scf.if gets rewritten to arith.select).
+X = {"a": [0]};
+Y = rbind(X, X);
+Z = rbind(rbind(X, X), X);
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    X = Y;
+else
+    X = Z;
+print(X);

test/api/cli/controlflow/if_14.txt

@@ -0,0 +1,3 @@
+Frame(2x1, [a:int64_t])
+0
+0

test/api/cli/controlflow/if_15.daphne

@@ -0,0 +1,9 @@
+// Update a list inside then-branch of if-statement with value computed outside if-statement (scf.if gets rewritten to arith.select).
+X = createList([0]);
+Y = append(X, [1]);
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    X = Y;
+print(X);

test/api/cli/controlflow/if_15.txt

@@ -0,0 +1,5 @@
+List(2, DenseMatrix, int64_t)
+DenseMatrix(1x1, int64_t)
+0
+DenseMatrix(1x1, int64_t)
+1

test/api/cli/controlflow/if_16.daphne

@@ -0,0 +1,12 @@
+// Update a list inside else-branch of if-statement with value computed outside if-statement (scf.if gets rewritten to arith.select).
+X = createList([0]);
+Y = append(X, [1]);
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    r = 99; # do something unrelated to X
+else
+    X = Y;
+print(r);
+print(X);

test/api/cli/controlflow/if_16.txt

@@ -0,0 +1,4 @@
+99
+List(1, DenseMatrix, int64_t)
+DenseMatrix(1x1, int64_t)
+0

test/api/cli/controlflow/if_17.daphne

@@ -0,0 +1,12 @@
+// Update a list inside then-branch and else-branch of if-statement with values computed outside if-statement (scf.if gets rewritten to arith.select).
+X = createList([0]);
+Y = append(X, [1]);
+Z = append(X, [2]);
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    X = Y;
+else
+    X = Z;
+print(X);

test/api/cli/controlflow/if_17.txt

@@ -0,0 +1,5 @@
+List(2, DenseMatrix, int64_t)
+DenseMatrix(1x1, int64_t)
+0
+DenseMatrix(1x1, int64_t)
+1

test/api/cli/controlflow/if_18.daphne

@@ -0,0 +1,9 @@
+// Update a string inside then-branch of if-statement with value computed outside if-statement (scf.if gets rewritten to arith.select).
+X = "a";
+Y = X + "b";
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    X = Y;
+print(X);

test/api/cli/controlflow/if_18.txt

@@ -0,0 +1 @@
+ab

test/api/cli/controlflow/if_19.daphne

@@ -0,0 +1,12 @@
+// Update a string inside else-branch of if-statement with value computed outside if-statement (scf.if gets rewritten to arith.select).
+X = "a";
+Y = X + "b";
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    r = 99; # do something unrelated to X
+else
+    X = Y;
+print(r);
+print(X);

test/api/cli/controlflow/if_19.txt

@@ -0,0 +1,2 @@
+99
+a

test/api/cli/controlflow/if_20.daphne

@@ -0,0 +1,12 @@
+// Update a string inside then-branch and else-branch of if-statement with values computed outside if-statement (scf.if gets rewritten to arith.select).
+X = "a";
+Y = X + "b";
+Z = X + "c";
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    X = Y;
+else
+    X = Z;
+print(X);

test/api/cli/controlflow/if_20.txt

@@ -0,0 +1 @@
+ab

test/api/cli/controlflow/if_9.daphne

@@ -0,0 +1,9 @@
+// Update a matrix inside then-branch of if-statement with value computed outside if-statement (scf.if gets rewritten to arith.select).
+X = [0];
+Y = X + 1;
+# r must be unknown at compile-time (otherwise, the entire "if" gets optimized away)
+# TODO The rand() might get optimized away at some point in the future (but not at the moment), because the result is clear.
+r = as.scalar(rand(1, 1, 0, 1, 1, -1));
+if(r)
+    X = Y;
+print(X);

test/api/cli/controlflow/if_9.txt

@@ -0,0 +1,2 @@
+DenseMatrix(1x1, int64_t)
+1