Correct long loops for wave-sensitive tracing (#2859)

Because VisitedPhis parameter to the recursive function to cull wave
sensitive blocks was not passed by reference, PHI nodes were getting
repeated. This corrects that issue and also adds bailouts for when no
break blocks are left or when the call instruction isn't in the current
function.

lib/HLSL/DxilPreparePasses.cpp

@@ -1079,12 +1079,12 @@ namespace {
 // a break conditional on dx.break that breaks out of a loop that contains WaveCI
 // LInfo is needed to determine loop contents. VisitedPhis is needed to prevent infinit looping.
 static void CullSensitiveBlocks(LoopInfo *LInfo, BasicBlock *WaveBB, BasicBlock *LastBB, Instruction *Inst,
-                                SmallPtrSet<Instruction *, 16> VisitedPhis,
+                                SmallPtrSet<Instruction *, 16> &VisitedPhis,
                                 SmallDenseMap<BasicBlock *, Instruction *, 16> &BreakBBs) {
   BasicBlock *BB = Inst->getParent();
   Loop *BreakLoop = LInfo->getLoopFor(BB);
   // If this instruction isn't in a loop, there is no need to track its sensitivity further
-  if (!BreakLoop)
+  if (!BreakLoop || BreakBBs.empty())
     return;
 
   // To prevent infinite looping, only visit each PHI once
@@ -1160,17 +1160,22 @@ public:
     SmallDenseMap<BasicBlock *, Instruction *, 16> BreakBBs;
     CollectBreakBlocks(BreakFunc, &F, BreakBBs);
 
+    if (BreakBBs.empty())
+      return false;
+
     // For each wave operation, remove all the dx.break blocks that are sensitive to it
     for (Function &IF : M->functions()) {
       HLOpcodeGroup opgroup = hlsl::GetHLOpcodeGroup(&IF);
       // Only consider wave-sensitive intrinsics or extintrinsics
-      if (IF.isDeclaration() && IsHLWaveSensitive(&IF) &&
+      if (IF.isDeclaration() && IsHLWaveSensitive(&IF) && !BreakBBs.empty() &&
           (opgroup == HLOpcodeGroup::HLIntrinsic || opgroup == HLOpcodeGroup::HLExtIntrinsic)) {
         // For each user of the function, trace all its users to remove the blocks
         for (User *U : IF.users()) {
           CallInst *CI = cast<CallInst>(U);
-          SmallPtrSet<Instruction *, 16> VisitedPhis;
-          CullSensitiveBlocks(LInfo, CI->getParent(), nullptr, CI, VisitedPhis, BreakBBs);
+          if (CI->getParent()->getParent() == &F) {
+            SmallPtrSet<Instruction *, 16> VisitedPhis;
+            CullSensitiveBlocks(LInfo, CI->getParent(), nullptr, CI, VisitedPhis, BreakBBs);
+          }
         }
       }
     }