[CUDA] Die gracefully when trying to output an LLVM alias.

[jlebar]

Summary

Previously, we would just output "foo = bar" in the assembly, and then
ptxas would choke. Now we die before emitting any invalid code.

We could check for aliases much earlier, e.g. during doInitialization.
But I figure it's better to emit as much code as we can and only die at
the last minute.

[echristo]

Personally I'd go with doInitialization just so we know earlier. Fail faster :)

-eric

[jlebar]

Die during doInitialization instead of doFinalization.

[jlebar]

In D16490#334527, @echristo wrote:

Personally I'd go with doInitialization just so we know earlier. Fail faster :)

Sure, done.

[echristo]

LGTM.

lib/Target/NVPTX/NVPTXAsmPrinter.cpp

bool NVPTXAsmPrinter::doFinalization(Module &M) {
   for (Module::global_iterator I = global_list.begin(), E = global_list.end();
        I != E; ++I)
     gv_array[i++] = &*I;
 
   // second, empty global_list
   while (!global_list.empty())
     global_list.remove(global_list.begin());
 
-  // call doFinalization
-  bool ret = AsmPrinter::doFinalization(M);
+  // Aliases are emitted during AsmPrinter::doFinalization(), so bail before
+  // then if we have any.
+  bool ret = false;
+  if (M.alias_size()) {
+    report_fatal_error("Module has aliases, which NVPTX does not support.");
+    ret = true; // error
+  }
+
+  if (!ret)
+    ret = AsmPrinter::doFinalization(M);
 
   // now we restore global variables
   for (i = 0; i < n; i++)
     global_list.insert(global_list.end(), gv_array[i]);
 
   clearAnnotationCache(&M);
 
   delete[] gv_array;

test/CodeGen/NVPTX/alias.ll

+; RUN: not llc < %s -march=nvptx -mcpu=sm_20 2>&1 | FileCheck %s
+
+; Check that llc dies gracefully when given an alias.
+
+define i32 @a() { ret i32 0 }
+; CHECK: ERROR: Module has aliases
+@b = internal alias i32 (), i32 ()* @a