[OpenMP] Add more verbose remarks for runtime folding

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.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D109627

Author: jhuber6

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

@@ -102,6 +102,11 @@ static cl::opt<bool> AlwaysInlineDeviceFunctions(
     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,
@@ -4034,11 +4039,25 @@ struct AAFoldRuntimeCallCallSiteReturned : AAFoldRuntimeCall {
     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;

openmp/docs/remarks/OMP180.rst

@@ -0,0 +1,38 @@
+.. _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

@@ -39,6 +39,7 @@ OpenMP Remarks
    OMP150
    OMP160
    OMP170
+   OMP180
 
 .. list-table::
    :widths: 15 15 70
@@ -107,3 +108,6 @@ OpenMP Remarks
    * - :ref:`OMP170 <omp170>`
      - Optimization
      - OpenMP runtime call <call> deduplicated.
+   * - :ref:`OMP180 <omp180>`
+     - Optimization
+     - Replacing OpenMP runtime call <call> with <value>.