llvm: Disable copy for SingleThreadExecutor

[Steelskin]

This is a workaround for the MSVC compiler, which attempts to generate a copy assignment operator implementation for classes marked as __declspec(dllexport). Explicitly marking the copy assignment operator as deleted works around the problem.

DevCom ticket: https://developercommunity.microsoft.com/t/Classes-marked-with-__declspecdllexport/11003192

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Fabrice de Gans (Steelskin)

Changes

This is a workaround for the MSVC compiler, which attempts to generate a copy assignment operator implementation for classes marked as __declspec(dllexport). Explicitly marking the copy assignment operator as deleted works around the problem.

DevCom ticket: https://developercommunity.microsoft.com/t/Classes-marked-with-__declspecdllexport/11003192

---

Full diff: https://github.com/llvm/llvm-project/pull/168782.diff

1 Files Affected:

• (modified) llvm/include/llvm/Support/ThreadPool.h (+7)

diff --git a/llvm/include/llvm/Support/ThreadPool.h b/llvm/include/llvm/Support/ThreadPool.h
index 1be7779f2c72c..933d3f43812ad 100644
--- a/llvm/include/llvm/Support/ThreadPool.h
+++ b/llvm/include/llvm/Support/ThreadPool.h
@@ -225,6 +225,13 @@ class LLVM_ABI SingleThreadExecutor : public ThreadPoolInterface {
   /// Blocking destructor: the pool will first execute the pending tasks.
   ~SingleThreadExecutor() override;
 
+  // Excplicitly disable copy. This is necessary for the MSVC LLVM_DYLIB build
+  // to work around a compiler bug where classes marked as
+  // `__declspec(dllexport)` cause the compiler to attempt to generate a copy
+  // assignment operator.
+  SingleThreadExecutor(const SingleThreadExecutor &) = delete;
+  SingleThreadExecutor &operator=(const SingleThreadExecutor &) = delete;
+
   /// Blocking wait for all the tasks to execute first
   void wait() override;
 

[github-actions]

🐧 Linux x64 Test Results

• 186451 tests passed
• 4868 tests skipped

[llvm-ci]

LLVM Buildbot has detected a new failure on builder lld-x86_64-ubuntu-fast running on as-builder-4 while building llvm at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/33/builds/26924

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: tools/llvm-exegesis/RISCV/rvv/filter.test' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 1
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput --opcode-name=PseudoVNCLIPU_WX_M1_MASK     --riscv-filter-config='vtype = {VXRM: rod, AVL: VLMAX, SEW: e(8|16), Policy: ta/mu}' --max-configs-per-opcode=1000 --min-instructions=10 | /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test
# executed command: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput --opcode-name=PseudoVNCLIPU_WX_M1_MASK '--riscv-filter-config=vtype = {VXRM: rod, AVL: VLMAX, SEW: e(8|16), Policy: ta/mu}' --max-configs-per-opcode=1000 --min-instructions=10
# .---command stderr------------
# | PseudoVNCLIPU_WX_M1_MASK: Failed to produce any snippet via: instruction has tied variables, avoiding Read-After-Write issue, picking random def and use registers not aliasing each other, for uses, one unique register for each position
# `-----------------------------
# executed command: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test
# `-----------------------------
# error: command failed with exit status: 2

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