[PATCH] D47023: Limit the number of phis in intptr/ptrint folding

[David Li via Phabricator via llvm-commits]

davidxl created this revision.
davidxl added a reviewer: mzolotukhin.

In rare cases when there are thousands of single use phis in a BB, the phi folding simplification can take excessive amount of time. Add an option to control the limit. Mostly NFC.


https://reviews.llvm.org/D47023

Files:
  lib/Transforms/InstCombine/InstCombinePHI.cpp


Index: lib/Transforms/InstCombine/InstCombinePHI.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -23,6 +23,10 @@
 
 #define DEBUG_TYPE "instcombine"
 
+static cl::opt<unsigned>
+MaxNumPhis("instcombine-max-num-phis", cl::init(512),
+           cl::desc("Maximum number phis to handle in intptr/ptrint folding"));
+
 /// The PHI arguments will be folded into a single operation with a PHI node
 /// as input. The debug location of the single operation will be the merged
 /// locations of the original PHI node arguments.
@@ -176,8 +180,11 @@
   assert(AvailablePtrVals.size() == PN.getNumIncomingValues() &&
          "Not enough available ptr typed incoming values");
   PHINode *MatchingPtrPHI = nullptr;
+  unsigned NumPhis = 0;
   for (auto II = BB->begin(), EI = BasicBlock::iterator(BB->getFirstNonPHI());
-       II != EI; II++) {
+       II != EI; II++, NumPhis++) {
+    if (NumPhis > MaxNumPhis)
+      return nullptr;
     PHINode *PtrPHI = dyn_cast<PHINode>(II);
     if (!PtrPHI || PtrPHI == &PN || PtrPHI->getType() != IntToPtr->getType())
       continue;


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