Iterate backwards to find all trivially dead ops

Author: ivanradanov

flang/lib/Optimizer/OpenMP/LowerWorkshare.cpp

@@ -200,7 +200,8 @@ static bool isTransitivelyUsedOutside(Value v, SingleRegion sr) {
 /// We clone pure operations in both the parallel and single blocks. this
 /// functions cleans them up if they end up with no uses
 static void cleanupBlock(Block *block) {
-  for (Operation &op : llvm::make_early_inc_range(*block))
+  for (Operation &op : llvm::make_early_inc_range(
+           llvm::make_range(block->rbegin(), block->rend())))
     if (isOpTriviallyDead(&op))
       op.erase();
 }

flang/test/Transforms/OpenMP/lower-workshare4.mlir

@@ -1,8 +1,33 @@
 // RUN: fir-opt --split-input-file --lower-workshare --allow-unregistered-dialect %s | FileCheck %s
 
-// Check that we cleanup unused pure operations from either the parallel or
-// single regions
+// Check that we cleanup unused pure operations from the parallel and single
+// regions
 
+// CHECK-LABEL:   func.func @wsfunc() {
+// CHECK:           %[[VAL_0:.*]] = fir.alloca i32
+// CHECK:           omp.parallel {
+// CHECK:             omp.single {
+// CHECK:               %[[VAL_1:.*]] = "test.test1"() : () -> i32
+// CHECK:               %[[VAL_2:.*]] = arith.constant 2 : index
+// CHECK:               %[[VAL_3:.*]] = arith.constant 3 : index
+// CHECK:               %[[VAL_4:.*]] = arith.addi %[[VAL_2]], %[[VAL_3]] : index
+// CHECK:               "test.test3"(%[[VAL_4]]) : (index) -> ()
+// CHECK:               omp.terminator
+// CHECK:             }
+// CHECK:             %[[VAL_5:.*]] = arith.constant 1 : index
+// CHECK:             %[[VAL_6:.*]] = arith.constant 42 : index
+// CHECK:             omp.wsloop nowait {
+// CHECK:               omp.loop_nest (%[[VAL_7:.*]]) : index = (%[[VAL_5]]) to (%[[VAL_6]]) inclusive step (%[[VAL_5]]) {
+// CHECK:                 "test.test2"() : () -> ()
+// CHECK:                 omp.yield
+// CHECK:               }
+// CHECK:               omp.terminator
+// CHECK:             }
+// CHECK:             omp.barrier
+// CHECK:             omp.terminator
+// CHECK:           }
+// CHECK:           return
+// CHECK:         }
 func.func @wsfunc() {
   %a = fir.alloca i32
   omp.parallel {
@@ -13,7 +38,9 @@ func.func @wsfunc() {
       %c42 = arith.constant 42 : index
 
       %c2 = arith.constant 2 : index
-      "test.test3"(%c2) : (index) -> ()
+      %c3 = arith.constant 3 : index
+      %add = arith.addi %c2, %c3 : index
+      "test.test3"(%add) : (index) -> ()
 
       omp.workshare_loop_wrapper {
         omp.loop_nest (%arg1) : index = (%c1) to (%c42) inclusive step (%c1) {
@@ -29,27 +56,4 @@ func.func @wsfunc() {
   return
 }
 
-// CHECK-LABEL:   func.func @wsfunc() {
-// CHECK:           %[[VAL_0:.*]] = fir.alloca i32
-// CHECK:           omp.parallel {
-// CHECK:             omp.single {
-// CHECK:               %[[VAL_1:.*]] = "test.test1"() : () -> i32
-// CHECK:               %[[VAL_2:.*]] = arith.constant 2 : index
-// CHECK:               "test.test3"(%[[VAL_2]]) : (index) -> ()
-// CHECK:               omp.terminator
-// CHECK:             }
-// CHECK:             %[[VAL_3:.*]] = arith.constant 1 : index
-// CHECK:             %[[VAL_4:.*]] = arith.constant 42 : index
-// CHECK:             omp.wsloop nowait {
-// CHECK:               omp.loop_nest (%[[VAL_5:.*]]) : index = (%[[VAL_3]]) to (%[[VAL_4]]) inclusive step (%[[VAL_3]]) {
-// CHECK:                 "test.test2"() : () -> ()
-// CHECK:                 omp.yield
-// CHECK:               }
-// CHECK:               omp.terminator
-// CHECK:             }
-// CHECK:             omp.barrier
-// CHECK:             omp.terminator
-// CHECK:           }
-// CHECK:           return
-// CHECK:         }