[opt][HIPSTDPAR] Handle __hipstdpar_hidden_malloc (#123150)

This patch adds support for replacing calls to
`__hipstdpar_hidden_malloc` with calls to `__libc_malloc`, similarly to
how we handle hidden `free`. A future paired change in the forwarding
header will leverage this capability in order to handle certain special
cases where it is not possible / desirable to allocate via the HIP
runtime.

Author: AlexVlx

llvm/lib/Transforms/HipStdPar/HipStdPar.cpp

@@ -299,6 +299,13 @@ HipStdParAllocationInterpositionPass::run(Module &M, ModuleAnalysisManager&) {
     }
   }
 
+  if (auto F = M.getFunction("__hipstdpar_hidden_malloc")) {
+    auto LibcMalloc = M.getOrInsertFunction(
+        "__libc_malloc", F->getFunctionType(), F->getAttributes());
+    F->replaceAllUsesWith(LibcMalloc.getCallee());
+
+    eraseFromModule(*F);
+  }
   if (auto F = M.getFunction("__hipstdpar_hidden_free")) {
     auto LibcFree = M.getOrInsertFunction("__libc_free", F->getFunctionType(),
                                           F->getAttributes());

llvm/test/Transforms/HipStdPar/allocation-interposition.ll

@@ -14,6 +14,8 @@ declare i32 @__hipstdpar_posix_aligned_alloc(ptr, i64, i64)
 
 declare void @__hipstdpar_hidden_free(ptr)
 
+declare ptr @__hipstdpar_hidden_malloc(i64)
+
 declare ptr @__hipstdpar_realloc(ptr, i64)
 
 declare ptr @__hipstdpar_realloc_array(ptr, i64, i64)