[OpenMP] Fix calculation of dependencies for multi-dimensional iteration space (#99347)

The expectation for multiple iterators used in a single depend clause
(`depend(iterator(i=0:5,j=0:5), in:x[i][j])`) is that the iterator space
is the product of the iteration vectors (25 in that case). The current
codeGen only works correctly, if `numIterators() = 1`. For more
iterators, the execution results in runtime assertions or segfaults.
The modified codeGen first calculates the iteration space, then
multiplies to the number of dependencies in the depend clause and
finally adds to the total number of iterator dependencies.

Author: jprotze

clang/lib/CodeGen/CGOpenMPRuntime.cpp

@@ -4259,14 +4259,18 @@ std::pair<llvm::Value *, Address> CGOpenMPRuntime::emitDependClause(
     // Include number of iterations, if any.
 
     if (const auto *IE = cast_or_null<OMPIteratorExpr>(D.IteratorExpr)) {
+      llvm::Value *ClauseIteratorSpace =
+          llvm::ConstantInt::get(CGF.IntPtrTy, 1);
       for (unsigned I = 0, E = IE->numOfIterators(); I < E; ++I) {
         llvm::Value *Sz = CGF.EmitScalarExpr(IE->getHelper(I).Upper);
         Sz = CGF.Builder.CreateIntCast(Sz, CGF.IntPtrTy, /*isSigned=*/false);
-        llvm::Value *NumClauseDeps = CGF.Builder.CreateNUWMul(
-            Sz, llvm::ConstantInt::get(CGF.IntPtrTy, D.DepExprs.size()));
-        NumOfRegularWithIterators =
-            CGF.Builder.CreateNUWAdd(NumOfRegularWithIterators, NumClauseDeps);
+        ClauseIteratorSpace = CGF.Builder.CreateNUWMul(Sz, ClauseIteratorSpace);
       }
+      llvm::Value *NumClauseDeps = CGF.Builder.CreateNUWMul(
+          ClauseIteratorSpace,
+          llvm::ConstantInt::get(CGF.IntPtrTy, D.DepExprs.size()));
+      NumOfRegularWithIterators =
+          CGF.Builder.CreateNUWAdd(NumOfRegularWithIterators, NumClauseDeps);
       HasRegularWithIterators = true;
       continue;
     }

clang/test/OpenMP/depend_iterator_bug.c

@@ -5,6 +5,7 @@
 
 int x[100];
 int y[100];
+int z[100][100];
 
 // CHECK-LABEL: @many_iterators_single_clause(
 // CHECK:    [[VLA:%.*]] = alloca [[STRUCT_KMP_DEPEND_INFO:%.*]], i64 10, align 16
@@ -24,3 +25,31 @@ void many_iterators_many_clauses(void) {
     {
     }
 }
+
+// CHECK-LABEL: @multidim_iterators_clause1(
+// CHECK:    [[VLA:%.*]] = alloca [[STRUCT_KMP_DEPEND_INFO:%.*]], i64 1, align 16
+// CHECK:    = call i32 @__kmpc_omp_task_with_deps(ptr {{.*}}, i32 {{.*}}, ptr {{.*}}, i32 1, ptr {{.*}}, i32 0, ptr null)
+void multidim_iterators_clause1(void) {
+    #pragma omp task depend(iterator(i=0:1, j=0:1), in: z[i][j])
+    {
+    }
+}
+
+// CHECK-LABEL: @multidim_iterators_offset_clause(
+// CHECK:    [[VLA:%.*]] = alloca [[STRUCT_KMP_DEPEND_INFO:%.*]], i64 1, align 16
+// CHECK:    = call i32 @__kmpc_omp_task_with_deps(ptr {{.*}}, i32 {{.*}}, ptr {{.*}}, i32 1, ptr {{.*}}, i32 0, ptr null)
+void multidim_iterators_offset_clause(void) {
+    #pragma omp task depend(iterator(i=5:6, j=10:11), in: z[i][j])
+    {
+    }
+}
+
+// CHECK-LABEL: @multidim_iterators_clause25(
+// CHECK:    [[VLA:%.*]] = alloca [[STRUCT_KMP_DEPEND_INFO:%.*]], i64 25, align 16
+// CHECK:    = call i32 @__kmpc_omp_task_with_deps(ptr {{.*}}, i32 {{.*}}, ptr {{.*}}, i32 25, ptr {{.*}}, i32 0, ptr null)
+void multidim_iterators_clause25(void) {
+    #pragma omp task depend(iterator(i=0:5, j=0:5), in: z[i][j])
+    {
+    }
+}
+

clang/test/OpenMP/task_codegen.c

@@ -139,7 +139,8 @@ for (int i = 0; i < 10; ++i)
   // CHECK: [[EB_SUB_2_ADD_1_SUB:%.+]] = sub i32 [[EB_SUB_2_ADD]], 1
   // CHECK: [[EB_SUB_2_ADD_1_SUB_2_DIV:%.+]] = udiv i32 [[EB_SUB_2_ADD_1_SUB]], 2
   // CHECK: [[ELEMS:%.+]] = zext i32 [[EB_SUB_2_ADD_1_SUB_2_DIV]] to i64
-  // CHECK: [[NELEMS:%.+]] = mul nuw i64 [[ELEMS]], 1
+  // CHECK: [[ELEMS2:%.+]] = mul nuw i64 [[ELEMS]], 1
+  // CHECK: [[NELEMS:%.+]] = mul nuw i64 [[ELEMS2]], 1
 
   // ITERATOR_TOTAL = NELEMS + 0;
   // CHECK: [[ITERATOR_TOTAL:%.+]] = add nuw i64 0, [[NELEMS]]