[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.

llvm/trunk/lib/Target/NVPTX/NVPTXAsmPrinter.cpp

bool NVPTXAsmPrinter::doInitialization(Module &M) {
   // rest of NVPTX isn't friendly to change subtargets per function and
   // so the default TargetMachine will have all of the options.
   const Triple &TT = TM.getTargetTriple();
   StringRef CPU = TM.getTargetCPU();
   StringRef FS = TM.getTargetFeatureString();
   const NVPTXTargetMachine &NTM = static_cast<const NVPTXTargetMachine &>(TM);
   const NVPTXSubtarget STI(TT, CPU, FS, NTM);
 
+  if (M.alias_size()) {
+    report_fatal_error("Module has aliases, which NVPTX does not support.");
+    return true; // error
+  }
+
   SmallString<128> Str1;
   raw_svector_ostream OS1(Str1);
 
   MMI = getAnalysisIfAvailable<MachineModuleInfo>();
 
   // We need to call the parent's one explicitly.
   //bool Result = AsmPrinter::doInitialization(M);
 

llvm/trunk/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