Report warning if a global atomic instruction operates on a nullptr

Global atomics with nullptr lead to GPU hang. Generating a warning to avoid
time-consuming debugging process.

Author: aratajew

IGC/Compiler/CISACodeGen/EmitVISAPass.cpp

@@ -14507,6 +14507,12 @@ void EmitPass::emitAtomicRaw(llvm::GenIntrinsicInst *pInst, Value *dstAddr,
     if (pllbuffer->getType()->getPointerAddressSpace() == ADDRESS_SPACE_GLOBAL)
     {
         m_currShader->SetHasGlobalAtomics();
+
+        // Global atomics with nullptr lead to GPU hang. Emit warning to avoid time-consuming debugging process.
+        if (resource.m_surfaceType == ESURFACE_STATELESS && isa<llvm::ConstantPointerNull>(pllbuffer))
+        {
+            m_pCtx->EmitWarning("Possible null pointer dereference! Atomic instruction operates on a nullptr.", pInst);
+        }
     }
 
     CVariable* pSrc0 = nullptr;
@@ -15300,7 +15306,9 @@ static void divergentBarrierCheck(
             I->print(SS, true);
             SS.flush();
             OS << '\n' << Repr;
-            Ctx.EmitError(OS, "Possible divergent barrier found", I);
+            OS << "\nerror: ";
+            Ctx.EmitMessage(OS, "Possible divergent barrier found", I);
+            OS << "\nerror: backend compiler failed build.\n";
         }
     }
 }

IGC/Compiler/CodeGenContext.cpp

@@ -718,10 +718,9 @@ namespace IGC
 #endif
     }
 
-    void CodeGenContext::EmitError(std::ostream &OS, const char* errorstr, const llvm::Value* context) const
+    void CodeGenContext::EmitMessage(std::ostream &OS, const char* messagestr, const llvm::Value* context) const
     {
-        OS << "\nerror: ";
-        OS << errorstr;
+        OS << messagestr;
         // Try to get debug location to print out the relevant info.
         if (const llvm::Instruction *I = llvm::dyn_cast_or_null<llvm::Instruction>(context)) {
             if (const llvm::DILocation *DL = I->getDebugLoc()) {
@@ -755,18 +754,19 @@ namespace IGC
                 }
             }
         }
-        OS << "\nerror: backend compiler failed build.\n";
     }
 
     void CodeGenContext::EmitError(const char* errorstr, const llvm::Value *context)
     {
-        EmitError(this->oclErrorMessage, errorstr, context);
+        this->oclErrorMessage << "\nerror: ";
+        EmitMessage(this->oclErrorMessage, errorstr, context);
+        this->oclErrorMessage << "\nerror: backend compiler failed build.\n";
     }
 
-    void CodeGenContext::EmitWarning(const char* warningstr)
+    void CodeGenContext::EmitWarning(const char* warningstr, const llvm::Value* context)
     {
         this->oclWarningMessage << "\nwarning: ";
-        this->oclWarningMessage << warningstr;
+        EmitMessage(this->oclWarningMessage, warningstr, context);
         this->oclWarningMessage << "\n";
     }
 

IGC/Compiler/CodeGenPublic.h

@@ -1076,9 +1076,9 @@ namespace IGC
         virtual ~CodeGenContext();
         void clear();
         void clearMD();
-        void EmitError(std::ostream &OS, const char* errorstr, const llvm::Value *context) const;
+        void EmitMessage(std::ostream &OS, const char* errorstr, const llvm::Value *context) const;
         void EmitError(const char* errorstr, const llvm::Value *context);
-        void EmitWarning(const char* warningstr);
+        void EmitWarning(const char* warningstr, const llvm::Value *context = nullptr);
         inline bool HasError() const { return !this->oclErrorMessage.str().empty(); }
         inline bool HasWarning() const { return !this->oclWarningMessage.str().empty(); }
         inline const std::string GetWarning() { return this->oclWarningMessage.str(); }

IGC/ocloc_tests/Builtins/atomics_with_null_ptr.cl

@@ -0,0 +1,22 @@
+/*========================== begin_copyright_notice ============================
+
+Copyright (C) 2023 Intel Corporation
+
+SPDX-License-Identifier: MIT
+
+============================= end_copyright_notice ===========================*/
+
+// RUN: ocloc compile -file %s -device dg2 -options "-cl-std=CL2.0" 2>&1 | FileCheck %s
+
+// CHECK: warning: Possible null pointer dereference! Atomic instruction operates on a nullptr.
+
+void func(generic int* generic_ptr)
+{
+    global int* global_ptr = to_global(generic_ptr);
+    atomic_store(global_ptr, 1);
+}
+
+kernel void test(local int* ptr)
+{
+    func(ptr);
+}