[LoopOptWG][LoopUnroll] Disable loop unroll when user explicitly asks for unroll-and-jam

[syzaara]

Summary

If a loop isn't forced to be unrolled, we want to avoid unrolling it when there is an explicit unroll-and-jam pragma.
This is to prevent automatic unrolling from interfering with the user requested transformation.

llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp

static LoopUnrollResult tryToUnrollLoop(
     Optional<bool> ProvidedAllowProfileBasedPeeling,
     Optional<unsigned> ProvidedFullUnrollMaxCount) {
   LLVM_DEBUG(dbgs() << "Loop Unroll: F["
                     << L->getHeader()->getParent()->getName() << "] Loop %"
                     << L->getHeader()->getName() << "\n");
   TransformationMode TM = hasUnrollTransformation(L);
   if (TM & TM_Disable)
     return LoopUnrollResult::Unmodified;
+
+  // If this loop isn't forced to be unrolled, avoid unrolling it when the
+  // parent loop has an explicit unroll-and-jam pragma. This is to prevent
+  // automatic unrolling from interfering with the user requested
+  // transformation.
+  Loop *ParentL = L->getParentLoop();
+  if (ParentL != NULL &&
+      hasUnrollAndJamTransformation(ParentL) == TM_ForcedByUser
+      && hasUnrollTransformation(L) != TM_ForcedByUser) {
+    LLVM_DEBUG(dbgs() << "Not unrolling loop since parent loop has"
+                      << " llvm.loop.unroll_and_jam.\n");
+    return LoopUnrollResult::Unmodified;
+  }
+
+  // If this loop isn't forced to be unrolled, avoid unrolling it when the
+  // loop has an explicit unroll-and-jam pragma. This is to prevent automatic
+  // unrolling from interfering with the user requested transformation.
+  if (hasUnrollAndJamTransformation(L) == TM_ForcedByUser
+      && hasUnrollTransformation(L) != TM_ForcedByUser) {
+    LLVM_DEBUG(
+      dbgs() << "  Not unrolling loop since it has llvm.loop.unroll_and_jam.\n");
+    return LoopUnrollResult::Unmodified;
+  }
+
   if (!L->isLoopSimplifyForm()) {
     LLVM_DEBUG(
         dbgs() << "  Not unrolling loop which is not in loop-simplify form.\n");
     return LoopUnrollResult::Unmodified;
   }
 
   // When automatic unrolling is disabled, do not unroll unless overridden for
   // this loop.

llvm/test/Transforms/LoopUnrollAndJam/pragma-disable-unroll.ll

+; RUN: opt -loop-unroll -debug-only=loop-unroll -S < %s  2>&1 | FileCheck %s
+; REQUIRES: asserts
+
+
+; CHECK: Loop Unroll: F[test]
+; CHECK-NEXT: Not unrolling loop since parent loop has llvm.loop.unroll_and_jam
+; CHECK: Loop Unroll: F[test]
+; CHECK-NEXT: Not unrolling loop since it has llvm.loop.unroll_and_jam
+
+define i32 @test() {
+for.body4.preheader.preheader:
+  br label %for.body4.preheader4
+
+for.body4.preheader4:                             ; preds = %for.cond.cleanup3, %for.body4.preheader.preheader
+  %indvars.iv28 = phi i64 [ %indvars.iv.next29, %for.cond.cleanup3 ], [ 0, %for.body4.preheader.preheader ]
+  br label %for.body4
+
+for.body4:                                        ; preds = %for.body4.preheader4, %for.body4
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body4 ], [ 0, %for.body4.preheader4 ]
+  tail call void @test2(i64 %indvars.iv28, i64 %indvars.iv)
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, 10
+  br i1 %exitcond.not, label %for.cond.cleanup3, label %for.body4
+
+for.cond.cleanup3:                                ; preds = %for.body4
+  %indvars.iv.next29 = add nuw nsw i64 %indvars.iv28, 1
+  %exitcond31.not = icmp eq i64 %indvars.iv.next29, 10
+  br i1 %exitcond31.not, label %for.cond.cleanup, label %for.body4.preheader4, !llvm.loop !1
+
+for.cond.cleanup:                                 ; preds = %for.cond.cleanup3
+  ret i32 55
+}
+
+
+; CHECK: F[test_02]
+; CHECK-NOT: Not unrolling loop since {{.*}}  llvm.loop.unroll_and_jam
+define i32 @test_02() {
+for.body4.preheader.preheader:
+  br label %for.body4.preheader4
+
+for.body4.preheader4:                             ; preds = %for.cond.cleanup3, %for.body4.preheader.preheader
+  %indvars.iv28 = phi i64 [ %indvars.iv.next29, %for.cond.cleanup3 ], [ 0, %for.body4.preheader.preheader ]
+  br label %for.body4
+
+for.body4:                                        ; preds = %for.body4.preheader4, %for.body4
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body4 ], [ 0, %for.body4.preheader4 ]
+  tail call void @test2(i64 %indvars.iv28, i64 %indvars.iv)
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, 10
+  br i1 %exitcond.not, label %for.cond.cleanup3, label %for.body4
+
+for.cond.cleanup3:                                ; preds = %for.body4
+  %indvars.iv.next29 = add nuw nsw i64 %indvars.iv28, 1
+  %exitcond31.not = icmp eq i64 %indvars.iv.next29, 10
+  br i1 %exitcond31.not, label %for.cond.cleanup, label %for.body4.preheader4, !llvm.loop !2
+
+for.cond.cleanup:                                 ; preds = %for.cond.cleanup3
+  ret i32 55
+}
+
+; CHECK:F[test_03]
+; CHECK-NOT: Not unrolling loop since {{.*}}  llvm.loop.unroll_and_jam
+define i32 @test_03() {
+for.body4.preheader.preheader:
+  br label %for.body4.preheader4
+
+for.body4.preheader4:                             ; preds = %for.cond.cleanup3, %for.body4.preheader.preheader
+  %indvars.iv28 = phi i64 [ %indvars.iv.next29, %for.cond.cleanup3 ], [ 0, %for.body4.preheader.preheader ]
+  br label %for.body4
+
+for.body4:                                        ; preds = %for.body4.preheader4, %for.body4
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body4 ], [ 0, %for.body4.preheader4 ]
+  tail call void @test2(i64 %indvars.iv28, i64 %indvars.iv)
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, 10
+  br i1 %exitcond.not, label %for.cond.cleanup3, label %for.body4
+
+for.cond.cleanup3:                                ; preds = %for.body4
+  %indvars.iv.next29 = add nuw nsw i64 %indvars.iv28, 1
+  %exitcond31.not = icmp eq i64 %indvars.iv.next29, 10
+  br i1 %exitcond31.not, label %for.cond.cleanup, label %for.body4.preheader4, !llvm.loop !3
+
+for.cond.cleanup:                                 ; preds = %for.cond.cleanup3
+  ret i32 55
+}
+
+declare void @test2(i64 signext, i64 signext)
+
+!1 = distinct !{!1, !4}
+!2 = distinct !{!1, !5}
+!3 = distinct !{!1, !6}
+!4 = !{!"llvm.loop.unroll_and_jam.count", i32 4}
+!5 = !{!"llvm.loop.unroll_and_jam.count", i32 1}
+!6 = !{!"llvm.loop.unroll_and_jam.disable"}