[polly][ScheduleOptimizer] Use IslMaxOperationsGuard helper instead of explicit restoration (#79303)

To fix long compile time issue of Schedule optimizer, patch #77280 sets
the upper cap on max ISL operations. In case of bailing out when ISL
quota is hit, error handling behavior was restored manually. This commit
replaces the restoration code with IslMaxOperationsGuard helper and also
removes redundant early return.

Author: kartcq

polly/lib/Transform/ScheduleOptimizer.cpp

@@ -868,23 +868,14 @@ static void runIslScheduleOptimizer(
     SC = SC.set_validity(Validity);
     SC = SC.set_coincidence(Validity);
 
-    // Save error handling behavior
-    long MaxOperations = isl_ctx_get_max_operations(Ctx);
-    isl_ctx_set_max_operations(Ctx, ScheduleComputeOut);
-    Schedule = SC.compute_schedule();
-    bool ScheduleQuota = false;
-    if (isl_ctx_last_error(Ctx) == isl_error_quota) {
-      isl_ctx_reset_error(Ctx);
-      LLVM_DEBUG(
-          dbgs() << "Schedule optimizer calculation exceeds ISL quota\n");
-      ScheduleQuota = true;
-    }
-    isl_options_set_on_error(Ctx, ISL_ON_ERROR_ABORT);
-    isl_ctx_reset_operations(Ctx);
-    isl_ctx_set_max_operations(Ctx, MaxOperations);
+    {
+      IslMaxOperationsGuard MaxOpGuard(Ctx, ScheduleComputeOut);
+      Schedule = SC.compute_schedule();
 
-    if (ScheduleQuota)
-      return;
+      if (MaxOpGuard.hasQuotaExceeded())
+        LLVM_DEBUG(
+            dbgs() << "Schedule optimizer calculation exceeds ISL quota\n");
+    }
 
     isl_options_set_on_error(Ctx, OnErrorStatus);
 

polly/test/ScheduleOptimizer/schedule_computeout.ll

@@ -1,8 +1,8 @@
-; RUN: opt %loadPolly -S -polly-optree -polly-delicm  -polly-opt-isl -polly-schedule-computeout=100000 -debug-only="polly-opt-isl" < %s 2>&1 | FileCheck %s
+; RUN: opt %loadPolly -S -polly-optree -polly-delicm  -polly-opt-isl -polly-schedule-computeout=10000 -debug-only="polly-opt-isl" < %s 2>&1 | FileCheck %s
 ; REQUIRES: asserts
 
 ; 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.
+; Max compute out is initialized to 300000, Here it is set to 10000 for test purpose.
 
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 target triple = "aarch64-unknown-linux-gnu"