Report error if intel_reqd_sub_group_size` cannot be satisfied

Without this change, IGC silently switches to SIMD16 for kernels with
nested stackcalls even though a kernel has `intel_reqd_sub_group_size(32)``
attribute attached

IGC/Compiler/CISACodeGen/OpenCLKernelCodeGen.cpp

@@ -643,6 +643,39 @@ namespace IGC
  return result;
  }
 
+ uint32_t COpenCLKernel::getReqdSubGroupSize(llvm::Function& F, MetaDataUtils* MDUtils) const
+ {
+ FunctionInfoMetaDataHandle funcInfoMD = MDUtils->getFunctionsInfoItem(&F);
+ int simd_size = funcInfoMD->getSubGroupSize()->getSIMDSize();
+
+ // Finds the kernel and get the group simd size from the kernel
+ if (m_FGA)
+ {
+ llvm::Function* Kernel = &F;
+ auto FG = m_FGA->getGroup(&F);
+ Kernel = FG->getHead();
+ funcInfoMD = MDUtils->getFunctionsInfoItem(Kernel);
+ simd_size = funcInfoMD->getSubGroupSize()->getSIMDSize();
+ }
+ return simd_size;
+ }
+
+ uint32_t COpenCLKernel::getMaxPressure(llvm::Function& F, MetaDataUtils* MDUtils) const
+ {
+ FunctionInfoMetaDataHandle funcInfoMD = MDUtils->getFunctionsInfoItem(&F);
+ unsigned int maxPressure = funcInfoMD->getMaxRegPressure()->getMaxPressure();
+
+ if (m_FGA)
+ {
+ llvm::Function* Kernel = &F;
+ auto FG = m_FGA->getGroup(&F);
+ Kernel = FG->getHead();
+ funcInfoMD = MDUtils->getFunctionsInfoItem(Kernel);
+ maxPressure = funcInfoMD->getMaxRegPressure()->getMaxPressure();
+ }
+ return maxPressure;
+ }
+
  void COpenCLKernel::CreateKernelArgInfo()
  {
  auto funcMDIt = m_Context->getModuleMetaData()->FuncMD.find(entry);
@@ -3659,7 +3692,25 @@ namespace IGC
 
  // Func and Perf checks pass, compile this SIMD
  if (simdStatus == SIMDStatus::SIMD_PASS)
+ {
  return true;
+ }
+ // Report an error if intel_reqd_sub_group_size cannot be satisfied
+ else
+ {
+ MetaDataUtils* pMdUtils = EP.getAnalysis<MetaDataUtilsWrapper>().getMetaDataUtils();
+ CodeGenContext* ctx = GetContext();
+ auto reqdSubGroupSize = getReqdSubGroupSize(F, pMdUtils);
+ if (reqdSubGroupSize == numLanes(simdMode))
+ {
+ ctx->EmitError(
+ (std::string("Cannot compile a kernel in the SIMD mode specified by intel_reqd_sub_group_size(") +
+ std::to_string(reqdSubGroupSize) +
+ std::string(")")).c_str(),
+ &F);
+ return false;
+ }
+ }
 
  // Functional failure, skip compiling this SIMD
  if (simdStatus == SIMDStatus::SIMD_FUNC_FAIL)
@@ -3682,28 +3733,16 @@ namespace IGC
  CodeGenContext* pCtx = GetContext();
  MetaDataUtils* pMdUtils = EP.getAnalysis<MetaDataUtilsWrapper>().getMetaDataUtils();
  FunctionInfoMetaDataHandle funcInfoMD = pMdUtils->getFunctionsInfoItem(&F);
- int simd_size = funcInfoMD->getSubGroupSize()->getSIMDSize();
+ uint32_t simd_size = getReqdSubGroupSize(F, pMdUtils);
  bool hasSubGroupForce = hasSubGroupIntrinsicPVC(F);
- unsigned int maxPressure = funcInfoMD->getMaxRegPressure()->getMaxPressure();
-
- // Finds the kernel and get the group simd size from the kernel
- if (m_FGA)
- {
- llvm::Function* Kernel = &F;
- auto FG = m_FGA->getGroup(&F);
- Kernel = FG->getHead();
- funcInfoMD = pMdUtils->getFunctionsInfoItem(Kernel);
- simd_size = funcInfoMD->getSubGroupSize()->getSIMDSize();
- maxPressure = funcInfoMD->getMaxRegPressure()->getMaxPressure();
- }
+ uint32_t maxPressure = getMaxPressure(F, pMdUtils);
 
  auto FG = m_FGA ? m_FGA->getGroup(&F) : nullptr;
  bool hasStackCall = FG && FG->hasStackCall();
  bool isIndirectGroup = FG && m_FGA->isIndirectCallGroup(FG);
  bool hasSubroutine = FG && !FG->isSingleIgnoringStackOverflowDetection() && !hasStackCall && !isIndirectGroup;
  bool forceLowestSIMDForStackCalls = IGC_IS_FLAG_ENABLED(ForceLowestSIMDForStackCalls) && (hasStackCall || isIndirectGroup);
 
-
  if (simd_size == 0)
  {
  if (maxPressure >= IGC_GET_FLAG_VALUE(ForceSIMDRPELimit) &&
@@ -3849,19 +3888,8 @@ namespace IGC
  MetaDataUtils* pMdUtils = EP.getAnalysis<MetaDataUtilsWrapper>().getMetaDataUtils();
  ModuleMetaData* modMD = pCtx->getModuleMetaData();
  FunctionInfoMetaDataHandle funcInfoMD = pMdUtils->getFunctionsInfoItem(&F);
- int simd_size = funcInfoMD->getSubGroupSize()->getSIMDSize();
- unsigned int maxPressure = funcInfoMD->getMaxRegPressure()->getMaxPressure();
-
- // Finds the kernel and get the group simd size from the kernel
- if (m_FGA)
- {
- llvm::Function* Kernel = &F;
- auto FG = m_FGA->getGroup(&F);
- Kernel = FG->getHead();
- funcInfoMD = pMdUtils->getFunctionsInfoItem(Kernel);
- simd_size = funcInfoMD->getSubGroupSize()->getSIMDSize();
- maxPressure = funcInfoMD->getMaxRegPressure()->getMaxPressure();
- }
+ uint32_t simd_size = getReqdSubGroupSize(F, pMdUtils);
+ uint32_t maxPressure = getMaxPressure(F, pMdUtils);
 
  // For simd variant functions, detect which SIMD sizes are needed
  if (compileFunctionVariants && F.hasFnAttribute("variant-function-def"))
@@ -3896,14 +3924,6 @@ namespace IGC
  bool hasIndirectCall = FG && FG->hasIndirectCall();
  if (hasNestedCall || hasIndirectCall || isIndirectGroup)
  {
- // If sub_group_size is set to 32, resize it to 16 so SIMD16 compilation will still succeed
- if (simd_size == 32)
- {
- pCtx->EmitWarning("Detected 'reqd_sub_group_size=32', but compiling to SIMD16 due to enabling CallWA, which does not support SIMD32 when nested/indirect calls are present.");
- llvm::Function* Kernel = FG->getHead();
- funcInfoMD = pMdUtils->getFunctionsInfoItem(Kernel);
- funcInfoMD->getSubGroupSize()->setSIMDSize(16);
- }
  pCtx->SetSIMDInfo(SIMD_SKIP_HW, simdMode, ShaderDispatchMode::NOT_APPLICABLE);
  return SIMDStatus::SIMD_FUNC_FAIL;
  }

IGC/Compiler/CISACodeGen/OpenCLKernelCodeGen.hpp

@@ -263,6 +263,9 @@ namespace IGC
  std::string getKernelArgTypeQualifier(const FunctionMetaData& funcMD, uint argIndex) const;
  std::string getKernelArgAddressQualifier(const FunctionMetaData& funcMD, uint argIndex) const;
  std::string getKernelArgAccessQualifier(const FunctionMetaData& funcMD, uint argIndex) const;
+ // Helper function to get SIMD size specified in intel_reqd_sub_group_size attribute
+ uint32_t getReqdSubGroupSize(llvm::Function& F, IGC::IGCMD::MetaDataUtils* MDUtils) const;
+ uint32_t getMaxPressure(llvm::Function& F, IGC::IGCMD::MetaDataUtils* MDUtils) const;
  };
 
  void CodeGen(OpenCLProgramContext* ctx);

IGC/ocloc_tests/features/reqd_sub_group_size/report_error.cl

@@ -0,0 +1,27 @@
+/*========================== begin_copyright_notice ============================
+
+Copyright (C) 2024 Intel Corporation
+
+SPDX-License-Identifier: MIT
+
+============================= end_copyright_notice ===========================*/
+
+// REQUIRES: dg2-supported
+// RUN: not ocloc compile -file %s -device dg2 | FileCheck %s
+
+// IGC enables EUFusion CallWA for DG2 when nested stackcalls or indirect calls
+// are present in a module. The workaround is not supported in SIMD32. This test
+// verifies if a proper error message is printed if CallWA is required and
+// intel_reqd_sub_group_size kernel attribute is set to 32.
+
+// CHECK: error: Cannot compile a kernel in the SIMD mode specified by intel_reqd_sub_group_size(32)
+// CHECK-NEXT: in kernel: 'test_simple'
+
+int fact(int n) {
+ return n < 2 ? 1 : n * fact(n - 1);
+}
+
+__attribute__((intel_reqd_sub_group_size(32)))
+kernel void test_simple(global int* out, int n) {
+ out[0] = fact(n);
+}