[ESIMD] Fix compilation from static libraries (#5826)

* [ESIMD] Fix compilation from static libraries.

sycl-post-link previously removed "llvm.used" global, but that was
not enough as the initializer of "llvm.used" was not deleted and
some elements of initializer used kernels.
As a result the GenXSPIRVWriterAdaptor did not transform the kernel
arguments properly thinking that the kernel was called from inside the module,
which was not true.
Removing the initializer fixed the issue.

Signed-off-by: Vyacheslav N Klochkov <[email protected]>
Co-authored-by: Mikhail Lychkov <[email protected]>

Author: v-klochkov

llvm/tools/sycl-post-link/sycl-post-link.cpp

@@ -47,6 +47,7 @@
 #include "llvm/Transforms/InstCombine/InstCombine.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Cloning.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
 
 #include <algorithm>
 #include <map>
@@ -833,6 +834,40 @@ class ModuleSplitter {
   size_t totalSplits() { return GMap.size(); }
 };
 
+// Removes the global variable "llvm.used" and returns true on success.
+// "llvm.used" is a global constant array containing references to kernels
+// available in the module and callable from host code. The elements of
+// the array are ConstantExpr bitcast to i8*.
+// The variable must be removed as it is a) has done the job to the moment
+// of this function call and b) the references to the kernels callable from
+// host must not have users.
+static bool removeSYCLKernelsConstRefArray(GlobalVariable *GV) {
+  assert(GV->getGlobalIdentifier() == "llvm.used" &&
+         "Unexpected global value is passed for removal, should be llvm.used");
+  assert(GV->user_empty() && "Unexpected llvm.used users");
+  Constant *Initializer = GV->getInitializer();
+  GV->setInitializer(nullptr);
+  GV->eraseFromParent();
+
+  // Destroy the initializer and all operands of it.
+  SmallVector<Constant *, 8> IOperands;
+  for (auto It = Initializer->op_begin(); It != Initializer->op_end(); It++)
+    IOperands.push_back(cast<Constant>(*It));
+  assert(llvm::isSafeToDestroyConstant(Initializer) &&
+         "Cannot remove initializer of llvm.used global");
+  Initializer->destroyConstant();
+  for (auto It = IOperands.begin(); It != IOperands.end(); It++) {
+    assert(llvm::isSafeToDestroyConstant(*It) &&
+           "Cannot remove an element of initializer of llvm.used global");
+    auto F = cast<Function>((*It)->getOperand(0));
+    (*It)->destroyConstant();
+    // Remove unused kernel declarations to avoid LLVM IR check fails.
+    if (F->isDeclaration())
+      F->eraseFromParent();
+  }
+  return true;
+}
+
 using TableFiles = std::map<StringRef, string_vector>;
 
 TableFiles processOneModule(std::unique_ptr<Module> M, bool IsEsimd,
@@ -849,11 +884,8 @@ TableFiles processOneModule(std::unique_ptr<Module> M, bool IsEsimd,
   // issue remove "llvm.used" from the input module before performing any other
   // actions.
   bool IsLLVMUsedRemoved = false;
-  if (GlobalVariable *GV = M->getGlobalVariable("llvm.used")) {
-    assert(GV->user_empty() && "unexpected llvm.used users");
-    GV->eraseFromParent();
-    IsLLVMUsedRemoved = true;
-  }
+  if (GlobalVariable *GV = M->getGlobalVariable("llvm.used"))
+    IsLLVMUsedRemoved = removeSYCLKernelsConstRefArray(GV);
 
   if (IsEsimd && LowerEsimd)
     lowerEsimdConstructs(*M);