[polly][ScheduleOptimizer] Fix long compile time(hang) reported in polly (#75141)

There is no upper cap set on current Schedule Optimizer to compute
schedule. In some cases a very long compile time taken to compute the
schedule resulting in hang kind of behavior. This patch introduces a
flag 'polly-schedule-computeout' to pass the capwhich is initialized to
300000. This patch handles the compute out cases by bailing out and
exiting gracefully.

Fixes #69090

2 files changed, 111 insertions, 1 deletions

diff --git a/polly/lib/Transform/ScheduleOptimizer.cpp b/polly/lib/Transform/ScheduleOptimizer.cpp
index 35a0a4d..5a0ea3b 100644
--- a/polly/lib/Transform/ScheduleOptimizer.cpp
+++ b/polly/lib/Transform/ScheduleOptimizer.cpp
@@ -96,6 +96,13 @@ static cl::opt<std::string>
                       cl::desc("Maximize the band depth (yes/no)"), cl::Hidden,
                       cl::init("yes"), cl::cat(PollyCategory));
 
+static cl::opt<int>
+    ScheduleComputeOut("polly-schedule-computeout",
+                       cl::desc("Bound the scheduler by maximal amount"
+                                "of computational steps. "),
+                       cl::Hidden, cl::init(300000), cl::ZeroOrMore,
+                       cl::cat(PollyCategory));
+
 static cl::opt<bool>
     GreedyFusion("polly-loopfusion-greedy",
                  cl::desc("Aggressively try to fuse everything"), cl::Hidden,
@@ -860,7 +867,16 @@ static void runIslScheduleOptimizer(
     SC = SC.set_proximity(Proximity);
     SC = SC.set_validity(Validity);
     SC = SC.set_coincidence(Validity);
-    Schedule = SC.compute_schedule();
+
+    {
+      IslMaxOperationsGuard MaxOpGuard(Ctx, ScheduleComputeOut);
+      Schedule = SC.compute_schedule();
+
+      if (MaxOpGuard.hasQuotaExceeded())
+        LLVM_DEBUG(
+            dbgs() << "Schedule optimizer calculation exceeds ISL quota\n");
+    }
+
     isl_options_set_on_error(Ctx, OnErrorStatus);
 
     ScopsRescheduled++;
diff --git a/polly/test/ScheduleOptimizer/schedule_computeout.ll b/polly/test/ScheduleOptimizer/schedule_computeout.ll
new file mode 100644
index 0000000..db46ef5
--- /dev/null
+++ b/polly/test/ScheduleOptimizer/schedule_computeout.ll
@@ -0,0 +1,94 @@
+; RUN: opt -S -polly-optree -polly-delicm  -polly-opt-isl -polly-schedule-computeout=100000 -debug-only="polly-opt-isl" < %s 2>&1 | FileCheck %s
+; Bailout if the computations of schedule compute exceeds the max scheduling quota.
+; Max compute out is initialized to 300000, Here it is set to 100000 for test purpose.
+
+@a = dso_local local_unnamed_addr global ptr null, align 8
+@b = dso_local local_unnamed_addr global ptr null, align 8
+@c = dso_local local_unnamed_addr global ptr null, align 8
+
+define dso_local void @foo(i32 noundef %I, i32 noundef %J, i32 noundef %K1, i32 noundef %K2, i32 noundef %L1, i32 noundef %L2) local_unnamed_addr {
+entry:
+  %j = alloca i32, align 4
+  store volatile i32 0, ptr %j, align 4
+  %j.0.j.0.j.0.54 = load volatile i32, ptr %j, align 4
+  %cmp55 = icmp slt i32 %j.0.j.0.j.0.54, %J
+  br i1 %cmp55, label %for.body.lr.ph, label %for.cond.cleanup
+
+for.body.lr.ph:                                   ; preds = %entry
+  %0 = load ptr, ptr @a, align 8
+  %1 = load ptr, ptr @b, align 8
+  %2 = load ptr, ptr %1, align 8
+  %cmp352 = icmp slt i32 %L1, %L2
+  %cmp750 = icmp slt i32 %K1, %K2
+  %3 = sext i32 %K1 to i64
+  %4 = sext i32 %L1 to i64
+  br label %for.body
+
+for.cond.cleanup:                                 ; preds = %for.cond.cleanup4, %entry
+  ret void
+
+for.body:                                         ; preds = %for.cond.cleanup4, %for.body.lr.ph
+  br i1 %cmp352, label %for.cond6.preheader.preheader, label %for.cond.cleanup4
+
+for.cond6.preheader.preheader:                    ; preds = %for.body
+  %wide.trip.count66 = sext i32 %L2 to i64
+  br label %for.cond6.preheader
+
+for.cond6.preheader:                              ; preds = %for.cond.cleanup8, %for.cond6.preheader.preheader
+  %indvars.iv61 = phi i64 [ %4, %for.cond6.preheader.preheader ], [ %indvars.iv.next62, %for.cond.cleanup8 ]
+  br i1 %cmp750, label %for.cond10.preheader.lr.ph, label %for.cond.cleanup8
+
+for.cond10.preheader.lr.ph:                       ; preds = %for.cond6.preheader
+  %5 = mul nsw i64 %indvars.iv61, 516
+  %6 = mul nsw i64 %indvars.iv61, 516
+  %wide.trip.count = sext i32 %K2 to i64
+  br label %for.cond10.preheader
+
+for.cond.cleanup4:                                ; preds = %for.cond.cleanup8, %for.body
+  %j.0.j.0.j.0.45 = load volatile i32, ptr %j, align 4
+  %inc34 = add nsw i32 %j.0.j.0.j.0.45, 1
+  store volatile i32 %inc34, ptr %j, align 4
+  %j.0.j.0.j.0. = load volatile i32, ptr %j, align 4
+  %cmp = icmp slt i32 %j.0.j.0.j.0., %J
+  br i1 %cmp, label %for.body, label %for.cond.cleanup
+
+for.cond10.preheader:                             ; preds = %for.cond.cleanup12, %for.cond10.preheader.lr.ph
+  %indvars.iv = phi i64 [ %3, %for.cond10.preheader.lr.ph ], [ %indvars.iv.next, %for.cond.cleanup12 ]
+  %7 = getelementptr float, ptr %0, i64 %indvars.iv
+  %arrayidx18 = getelementptr float, ptr %7, i64 %5
+  %8 = load float, ptr %arrayidx18, align 4
+  br label %for.cond14.preheader
+
+for.cond.cleanup8:                                ; preds = %for.cond.cleanup12, %for.cond6.preheader
+  %indvars.iv.next62 = add nsw i64 %indvars.iv61, 1
+  %exitcond67.not = icmp eq i64 %indvars.iv.next62, %wide.trip.count66
+  br i1 %exitcond67.not, label %for.cond.cleanup4, label %for.cond6.preheader
+
+for.cond14.preheader:                             ; preds = %for.cond.cleanup16, %for.cond10.preheader
+  %m.049 = phi i32 [ -2, %for.cond10.preheader ], [ %inc21, %for.cond.cleanup16 ]
+  %sum.048 = phi float [ 0.000000e+00, %for.cond10.preheader ], [ %add19, %for.cond.cleanup16 ]
+  br label %for.body17
+
+for.cond.cleanup12:                               ; preds = %for.cond.cleanup16
+  %9 = getelementptr float, ptr %2, i64 %indvars.iv
+  %arrayidx26 = getelementptr float, ptr %9, i64 %6
+  store float %add19, ptr %arrayidx26, align 4
+  %indvars.iv.next = add nsw i64 %indvars.iv, 1
+  %exitcond60.not = icmp eq i64 %indvars.iv.next, %wide.trip.count
+  br i1 %exitcond60.not, label %for.cond.cleanup8, label %for.cond10.preheader
+
+for.cond.cleanup16:                               ; preds = %for.body17
+  %inc21 = add nsw i32 %m.049, 1
+  %exitcond56.not = icmp eq i32 %inc21, 3
+  br i1 %exitcond56.not, label %for.cond.cleanup12, label %for.cond14.preheader
+
+for.body17:                                       ; preds = %for.body17, %for.cond14.preheader
+  %n.047 = phi i32 [ -2, %for.cond14.preheader ], [ %inc, %for.body17 ]
+  %sum.146 = phi float [ %sum.048, %for.cond14.preheader ], [ %add19, %for.body17 ]
+  %add19 = fadd float %sum.146, %8
+  %inc = add nsw i32 %n.047, 1
+  %exitcond.not = icmp eq i32 %inc, 3
+  br i1 %exitcond.not, label %for.cond.cleanup16, label %for.body17
+}
+
+; CHECK: Schedule optimizer calculation exceeds ISL quota