MemCpyOpt: don't create new addrspacecasts

[escha]

Summary

It's not generally safe to create new addrspace casts in the optimizer (since not all such addrspace casts are legal on any given target), so given that we don't currently have a generic way to check, bail instead of creating them.

This fixes a problem on an out of tree target where memcpyopt creates invalid addrspace casts in order to "cleverly" eliminate a memcpy.

[arsenm]

test/Transforms/MemCpyOpt/memcpy.ll

207–213

How about more tests, where the sources are addrspacecasted to the same address space?

[arsenm]

LGTM

lib/Transforms/Scalar/MemCpyOptimizer.cpp

bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpy, Value *cpyDest,
   AliasAnalysis &AA = LookupAliasAnalysis();
   ModRefInfo MR = AA.getModRefInfo(C, cpyDest, srcSize);
   // If necessary, perform additional analysis.
   if (MR != MRI_NoModRef)
     MR = AA.callCapturesBefore(C, cpyDest, srcSize, &DT);
   if (MR != MRI_NoModRef)
     return false;
 
+  // We can't create address space casts here because we don't know if they're
+  // safe for the target.
+  if (cpySrc->getType()->getPointerAddressSpace() !=
+      cpyDest->getType()->getPointerAddressSpace())
+    return false;
+  for (unsigned i = 0; i < CS.arg_size(); ++i)
+    if (CS.getArgument(i)->stripPointerCasts() == cpySrc &&
+        cpySrc->getType()->getPointerAddressSpace() !=
+        CS.getArgument(i)->getType()->getPointerAddressSpace())
+      return false;
+
   // All the checks have passed, so do the transformation.
   bool changedArgument = false;
   for (unsigned i = 0; i < CS.arg_size(); ++i)
     if (CS.getArgument(i)->stripPointerCasts() == cpySrc) {
       Value *Dest = cpySrc->getType() == cpyDest->getType() ?  cpyDest
         : CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
                                       cpyDest->getName(), C);
       changedArgument = true;

test/Transforms/MemCpyOpt/memcpy.ll

define void @test10(%opaque* noalias nocapture sret %x, i32 %y) {
   store i32 %y, i32* %a
   call void @foo(i32* noalias nocapture %a)
   %c = load i32, i32* %a
   %d = bitcast %opaque* %x to i32*
   store i32 %c, i32* %d
   ret void
 }
 
+; don't create new addressspacecasts when we don't know they're safe for the target
+define void @test11(i8 addrspace(1)* nocapture dereferenceable(80) %P) {
+  %A = alloca [20 x i32], align 4
+  %a = bitcast [20 x i32]* %A to i8*
+  call void @llvm.memset.p0i8.i64(i8* %a, i8 0, i64 80, i32 4, i1 false)
+  call void @llvm.memcpy.p1i8.p0i8.i64(i8 addrspace(1)* %P, i8* %a, i64 80, i32 4, i1 false)
+  ret void
+; CHECK-LABEL: @test11(
+; CHECK-NOT: addrspacecast
+}
+
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind
+declare void @llvm.memcpy.p1i8.p0i8.i64(i8 addrspace(1)* nocapture, i8* nocapture, i64, i32, i1) nounwind
+
 declare void @f1(%struct.big* nocapture sret)
 declare void @f2(%struct.big*)
 
 ; CHECK: attributes [[NUW]] = { nounwind }
 ; CHECK: attributes #1 = { argmemonly nounwind }
 ; CHECK: attributes #2 = { nounwind ssp }
 ; CHECK: attributes #3 = { nounwind ssp uwtable }