[OpenMP] Add more verbose remarks for runtime folding

[jhuber6]

Summary

We peform runtime folding, but do not currently emit remarks when it is
performed. This is because it comes from the runtime library and is
beyond the users control. However, people may still wish to view this
and similar information easily, so we can enable this behaviour using a
special flag to enable verbose remarks.

[jhuber6]

Changing 'Folding' to 'Replacing'.

[jdoerfert]

LG, thanks.

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

static cl::opt<bool> PrintModuleAfterOptimizations(
     cl::desc("Print the current module after OpenMP optimizations."),
     cl::Hidden, cl::init(false));
 
 static cl::opt<bool> AlwaysInlineDeviceFunctions(
     "openmp-opt-inline-device", cl::ZeroOrMore,
     cl::desc("Inline all applicible functions on the device."), cl::Hidden,
     cl::init(false));
 
+static cl::opt<bool>
+    EnableVerboseRemarks("openmp-opt-verbose-remarks", cl::ZeroOrMore,
+                         cl::desc("Enables more verbose remarks."), cl::Hidden,
+                         cl::init(false));
+
 STATISTIC(NumOpenMPRuntimeCallsDeduplicated,
           "Number of OpenMP runtime calls deduplicated");
 STATISTIC(NumOpenMPParallelRegionsDeleted,
           "Number of OpenMP parallel regions deleted");
 STATISTIC(NumOpenMPRuntimeFunctionsIdentified,
           "Number of OpenMP runtime functions identified");
 STATISTIC(NumOpenMPRuntimeFunctionUsesIdentified,
           "Number of OpenMP runtime function uses identified");
ChangeStatus updateImpl(Attributor &A) override {
 
     return Changed;
   }
 
   ChangeStatus manifest(Attributor &A) override {
     ChangeStatus Changed = ChangeStatus::UNCHANGED;
 
     if (SimplifiedValue.hasValue() && SimplifiedValue.getValue()) {
-      Instruction &CB = *getCtxI();
-      A.changeValueAfterManifest(CB, **SimplifiedValue);
-      A.deleteAfterManifest(CB);
+      Instruction &I = *getCtxI();
+      A.changeValueAfterManifest(I, **SimplifiedValue);
+      A.deleteAfterManifest(I);
+
+      CallBase *CB = dyn_cast<CallBase>(&I);
+      auto Remark = [&](OptimizationRemark OR) {
+        if (auto *C = dyn_cast<ConstantInt>(*SimplifiedValue))
+          return OR << "Replacing OpenMP runtime call "
+                    << CB->getCalledFunction()->getName() << " with "
+                    << ore::NV("FoldedValue", C->getZExtValue()) << ".";
+        else
+          return OR << "Replacing OpenMP runtime call "
+                    << CB->getCalledFunction()->getName() << ".";
+      };
+
+      if (CB && EnableVerboseRemarks)
+        A.emitRemark<OptimizationRemark>(CB, "OMP180", Remark);
 
-      LLVM_DEBUG(dbgs() << TAG << "Folding runtime call: " << CB << " with "
+      LLVM_DEBUG(dbgs() << TAG << "Replacing runtime call: " << I << " with "
                         << **SimplifiedValue << "\n");
 
       Changed = ChangeStatus::CHANGED;
     }
 
     return Changed;
   }
 

openmp/docs/remarks/OMP180.rst

+.. _omp180:
+
+Replacing OpenMP runtime call <call> with <value>.
+====================================================================
+
+This optimization remark indicates that analysis determined an OpenMP runtime 
+calls can be replaced with a constant value. This can occur when an OpenMP 
+runtime call that queried some internal state was found to always return a 
+single value after analysis.
+
+Example
+-------
+
+This optimization will trigger for most target regions to simplify the runtime 
+once certain constants are known. This will trigger for internal runtime 
+functions so it requires enabling verbose remarks with 
+`-openmp-opt-verbose-remarks`.
+
+.. code-block:: c++
+
+  void foo() {
+  #pragma omp target parallel
+    { }
+  }
+
+.. code-block:: console
+
+  $ clang test.c -fopenmp -fopenmp-targets=nvptx64 -O1 -Rpass=openmp-opt \
+    -mllvm -openmp-opt-verbose-remarks
+  remark: Replacing runtime call __kmpc_is_spmd_exec_mode with 1. [OMP180] [-Rpass=openmp-opt]
+  remark: Replacing runtime call __kmpc_is_spmd_exec_mode with 1. [OMP180] [-Rpass=openmp-opt]
+  remark: Replacing runtime call __kmpc_parallel_level with 1. [OMP180] [-Rpass=openmp-opt]
+  remark: Replacing runtime call __kmpc_parallel_level with 1. [OMP180] [-Rpass=openmp-opt]
+
+Diagnostic Scope
+----------------
+
+OpenMP optimization remark.

openmp/docs/remarks/OptimizationRemarks.rst

.. toctree::
    OMP130
    OMP131
    OMP132
    OMP133
    OMP140
    OMP150
    OMP160
    OMP170
+   OMP180
 
 .. list-table::
    :widths: 15 15 70
    :header-rows: 1
 
    * - Diagnostics Number
      - Diagnostics Kind
      - Diagnostics Description
* - :ref:`OMP150 <omp150>`
      - Optimization
      - Parallel region merged with parallel region at <location>.
    * - :ref:`OMP160 <omp160>`
      - Optimization
      - Removing parallel region with no side-effects.
    * - :ref:`OMP170 <omp170>`
      - Optimization
      - OpenMP runtime call <call> deduplicated.
+   * - :ref:`OMP180 <omp180>`
+     - Optimization
+     - Replacing OpenMP runtime call <call> with <value>.