[Attributor] Adjust and test the iteration bound of tests

Summary:
Try to verify how many iterations we need for a fixpoint in our tests.
This patch adjust the way we count to make it easier to follow. It also
adjusts the bounds to actually account for a fixpoint and not only the
minimum number to pass all checks.

Reviewers: uenoku, sstefan1

Subscribers: hiraditya, bollu, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66757

llvm-svn: 369945

1 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index ebe4fba0856..a6e8e528fd0 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -107,6 +107,10 @@ static cl::opt<unsigned>
     MaxFixpointIterations("attributor-max-iterations", cl::Hidden,
                           cl::desc("Maximal number of fixpoint iterations."),
                           cl::init(32));
+static cl::opt<bool> VerifyMaxFixpointIterations(
+    "attributor-max-iterations-verify", cl::Hidden,
+    cl::desc("Verify that max-iterations is a tight bound for a fixpoint"),
+    cl::init(false));
 
 static cl::opt<bool> DisableAttributor(
     "attributor-disable", cl::Hidden,
@@ -2509,6 +2513,10 @@ ChangeStatus Attributor::run() {
       Worklist.insert(QuerriedAAs.begin(), QuerriedAAs.end());
     }
 
+    LLVM_DEBUG(dbgs() << "[Attributor] #Iteration: " << IterationCounter
+                      << ", Worklist+Dependent size: " << Worklist.size()
+                      << "\n");
+
     // Reset the changed set.
     ChangedAAs.clear();
 
@@ -2529,7 +2537,7 @@ ChangeStatus Attributor::run() {
     Worklist.clear();
     Worklist.insert(ChangedAAs.begin(), ChangedAAs.end());
 
-  } while (!Worklist.empty() && ++IterationCounter < MaxFixpointIterations);
+  } while (!Worklist.empty() && IterationCounter++ < MaxFixpointIterations);
 
   size_t NumFinalAAs = AllAbstractAttributes.size();
 
@@ -2537,6 +2545,10 @@ ChangeStatus Attributor::run() {
                     << IterationCounter << "/" << MaxFixpointIterations
                     << " iterations\n");
 
+  if (VerifyMaxFixpointIterations && IterationCounter != MaxFixpointIterations)
+    llvm_unreachable("The fixpoint was not reached with exactly the number of "
+                     "specified iterations!");
+
   bool FinishedAtFixpoint = Worklist.empty();
 
   // Reset abstract arguments not settled in a sound fixpoint by now. This