[WinEH] Set NoModuleLevelChanges in clone flags

[JosephTremoulet]

Summary

This is necessary to keep the cloner from making bogus copies of debug
metadata attached to the IR it is cloning.
Also, avoid running RemapInstruction over all instructions in the common
case that no cloning was performed.

[JosephTremoulet]

use the conventional merge behavior (2/warning) for the debug info version flag

[majnemer]

LGTM

lib/CodeGen/WinEHPrepare.cpp

for (BasicBlock *BB : BlocksInFunclet) {
 
       // Add basic block mapping.
       VMap[BB] = CBB;
 
       // Record delta operations that we need to perform to our color mappings.
       Orig2Clone[BB] = CBB;
     }
 
+    // If nothing was cloned, we're done cloning in this funclet.
+    if (Orig2Clone.empty())
+      continue;
+
     // Update our color mappings to reflect that one block has lost a color and
     // another has gained a color.
     for (auto &BBMapping : Orig2Clone) {
       BasicBlock *OldBlock = BBMapping.first;
       BasicBlock *NewBlock = BBMapping.second;
 
       BlocksInFunclet.insert(NewBlock);
       BlockColors[NewBlock].insert(FuncletPadBB);
 
       BlocksInFunclet.erase(OldBlock);
       BlockColors[OldBlock].erase(FuncletPadBB);
     }
 
-    // Loop over all of the instructions in the function, fixing up operand
+    // Loop over all of the instructions in this funclet, fixing up operand
     // references as we go.  This uses VMap to do all the hard work.
     for (BasicBlock *BB : BlocksInFunclet)
       // Loop over all instructions, fixing each one as we find it...
       for (Instruction &I : *BB)
-        RemapInstruction(&I, VMap, RF_IgnoreMissingEntries);
+        RemapInstruction(&I, VMap,
+                         RF_IgnoreMissingEntries | RF_NoModuleLevelChanges);
 
     // Check to see if SuccBB has PHI nodes. If so, we need to add entries to
     // the PHI nodes for NewBB now.
     for (auto &BBMapping : Orig2Clone) {
       BasicBlock *OldBlock = BBMapping.first;
       BasicBlock *NewBlock = BBMapping.second;
       for (BasicBlock *SuccBB : successors(NewBlock)) {
         for (Instruction &SuccI : *SuccBB) {

test/CodeGen/WinEH/wineh-cloning.ll

 }
 ; merge.end will get cloned for outer and inner, but is implausible
 ; from inner, so the invoke @f() in inner's copy of merge should be
 ; rewritten to call @f()
 ; CHECK-LABEL: define void @test11()
 ; CHECK:      %inner = cleanuppad []
 ; CHECK-NEXT: call void @f()
 ; CHECK-NEXT: unreachable
+
+define void @test12() personality i32 (...)* @__CxxFrameHandler3 {
+entry:
+  invoke void @f()
+    to label %cont unwind label %left, !dbg !8
+cont:
+  invoke void @f()
+    to label %exit unwind label %right
+left:
+  cleanuppad []
+  br label %join
+right:
+  cleanuppad []
+  br label %join
+join:
+  ; This call will get cloned; make sure we can handle cloning
+  ; instructions with debug metadata attached.
+  call void @f(), !dbg !9
+  unreachable
+exit:
+  ret void
+}
+
+; Make sure the DISubprogram doesn't get cloned
+; CHECK-LABEL: !llvm.module.flags
+; CHECK-NOT: !DISubprogram
+; CHECK: !{{[0-9]+}} = distinct !DISubprogram(name: "test12"
+; CHECK-NOT: !DISubprogram
+!llvm.module.flags = !{!0}
+!llvm.dbg.cu = !{!1}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !2, producer: "compiler", isOptimized: false, runtimeVersion: 0, emissionKind: 1, enums: !3, subprograms: !4)
+!2 = !DIFile(filename: "test.cpp", directory: ".")
+!3 = !{}
+!4 = !{!5}
+!5 = distinct !DISubprogram(name: "test12", scope: !2, file: !2, type: !6, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, function: void ()* @test12, variables: !3)
+!6 = !DISubroutineType(types: !7)
+!7 = !{null}
+!8 = !DILocation(line: 1, scope: !5)
+!9 = !DILocation(line: 2, scope: !5)