[PATCH] D47949: [callsitesplit] Limit the # of predecessors walk when recording condition

[Xin Tong via Phabricator via llvm-commits]

trentxintong created this revision.
trentxintong added reviewers: fhahn, junbuml.

We have some pathological cases (generated by machine) which
callsite splitting chokes on.


Repository:
  rL LLVM

https://reviews.llvm.org/D47949

Files:
  lib/Transforms/Scalar/CallSiteSplitting.cpp


Index: lib/Transforms/Scalar/CallSiteSplitting.cpp
===================================================================
--- lib/Transforms/Scalar/CallSiteSplitting.cpp
+++ lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -84,6 +84,15 @@
                                   "their cost is below DuplicationThreshold"),
                          cl::init(5));
 
+
+/// Only allow N level of predecessors to be walked.
+static cl::opt<unsigned>
+    PredecessorWalkThreshold("callsite-predecessor-walk-threshold", cl::Hidden,
+                         cl::desc("Only allow N number of predecessors to be"
+                                  "walked"),
+                         cl::init(16));
+
+
 static void addNonNullAttribute(CallSite CS, Value *Op) {
   unsigned ArgNo = 0;
   for (auto &I : CS.args()) {
@@ -152,6 +161,7 @@
 /// x == 1 and x == 0, the first condition will be used.
 static void recordConditions(CallSite CS, BasicBlock *Pred,
                              ConditionsTy &Conditions) {
+  uint32_t PredWalked = 0;
   recordCondition(CS, Pred, CS.getInstruction()->getParent(), Conditions);
   BasicBlock *From = Pred;
   BasicBlock *To = Pred;
@@ -161,6 +171,9 @@
     recordCondition(CS, From, To, Conditions);
     Visited.insert(From);
     To = From;
+    // Make sure we do not traverse too many predecessors up the CFG.
+    if (++PredWalked > PredecessorWalkThreshold)
+      break;
   }
 }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D47949.150527.patch
Type: text/x-patch
Size: 1413 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180608/a88a793c/attachment.bin>