[llvm] 58725c1 - [OpenMP] Introduce RAII to protect certain RTL calls from DCE

[via llvm-commits]

Author: Joseph Huber
Date: 2021-07-25T14:15:47-04:00
New Revision: 58725c12bb2746a3f82b4aafc84ff9284e4a991e

URL: https://github.com/llvm/llvm-project/commit/58725c12bb2746a3f82b4aafc84ff9284e4a991e
DIFF: https://github.com/llvm/llvm-project/commit/58725c12bb2746a3f82b4aafc84ff9284e4a991e.diff

LOG: [OpenMP] Introduce RAII to protect certain RTL calls from DCE

This patch introduces a new RAII struct that will temporarily make an OpenMP
RTL function have external linkage. This is done before the attributor is
invoked to prevent it from incorrectly removing some function definitions that
we will use later. For example, if we determine all calls to one function are
dead, because it has internal linkage it can safely be removed. Later when we
try to get an instance to that function to modify the source using
`getOrCreateRuntimeFunction` we will then get an empty declaration for that
function that won't be defined anywhere. This patch prevents this from
occurring.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D106707

Added: 
    

Modified: 
    llvm/lib/Transforms/IPO/OpenMPOpt.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/IPO/OpenMPOpt.cpp b/llvm/lib/Transforms/IPO/OpenMPOpt.cpp
index 1031a55886d7..3d03fc546f5c 100644
--- a/llvm/lib/Transforms/IPO/OpenMPOpt.cpp
+++ b/llvm/lib/Transforms/IPO/OpenMPOpt.cpp
@@ -1760,6 +1760,32 @@ struct OpenMPOpt {
           [&]() { return RemarkCB(RemarkKind(DEBUG_TYPE, RemarkName, F)); });
   }
 
+  /// RAII struct to temporarily change an RTL function's linkage to external.
+  /// This prevents it from being mistakenly removed by other optimizations.
+  struct ExternalizationRAII {
+    ExternalizationRAII(OMPInformationCache &OMPInfoCache,
+                        RuntimeFunction RFKind)
+        : OMPInfoCache(OMPInfoCache),
+          Declaration(OMPInfoCache.RFIs[RFKind].Declaration) {
+      if (!Declaration)
+        return;
+
+      LinkageType = Declaration->getLinkage();
+      Declaration->setLinkage(GlobalValue::ExternalLinkage);
+    }
+
+    ~ExternalizationRAII() {
+      if (!Declaration)
+        return;
+
+      Declaration->setLinkage(LinkageType);
+    }
+
+    OMPInformationCache &OMPInfoCache;
+    Function *Declaration;
+    GlobalValue::LinkageTypes LinkageType;
+  };
+
   /// The underlying module.
   Module &M;
 
@@ -1784,6 +1810,14 @@ struct OpenMPOpt {
     if (SCC.empty())
       return false;
 
+    // Temporarily make these function have external linkage so the Attributor
+    // doesn't remove them when we try to look them up later.
+    ExternalizationRAII Parallel(OMPInfoCache, OMPRTL___kmpc_kernel_parallel);
+    ExternalizationRAII EndParallel(OMPInfoCache,
+                                    OMPRTL___kmpc_kernel_end_parallel);
+    ExternalizationRAII BarrierSPMD(OMPInfoCache,
+                                    OMPRTL___kmpc_barrier_simple_spmd);
+
     registerAAs(IsModulePass);
 
     ChangeStatus Changed = A.run();