Do not copy gigantic switch instructions
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12441 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/TailDuplication.cpp b/lib/Transforms/Scalar/TailDuplication.cpp
index a3980b3..00d7f26 100644
--- a/lib/Transforms/Scalar/TailDuplication.cpp
+++ b/lib/Transforms/Scalar/TailDuplication.cpp
@@ -91,7 +91,8 @@
if (Dest == BI->getParent()) return false; // Do not loop infinitely!
// Do not inline a block if we will just get another branch to the same block!
- if (BranchInst *DBI = dyn_cast<BranchInst>(Dest->getTerminator()))
+ TerminatorInst *DTI = Dest->getTerminator();
+ if (BranchInst *DBI = dyn_cast<BranchInst>(DTI))
if (DBI->isUnconditional() && DBI->getSuccessor(0) == Dest)
return false; // Do not loop infinitely!
@@ -110,6 +111,15 @@
for (unsigned Size = 0; I != Dest->end(); ++Size, ++I)
if (Size == 6) return false; // The block is too large...
+
+ // Do not tail duplicate a block that has thousands of successors into a block
+ // with a single successor if the block has many other predecessors. This can
+ // cause an N^2 explosion in CFG edges (and PHI node entries), as seen in
+ // cases that have a large number of indirect gotos.
+ if (DTI->getNumSuccessors() > 8)
+ if (std::distance(PI, PE) * DTI->getNumSuccessors() > 128)
+ return false;
+
return true;
}
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 089d0ac..09153ed 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -331,8 +331,15 @@
// isValueEqualityComparison - Return true if the specified terminator checks to
// see if a value is equal to constant integer value.
static Value *isValueEqualityComparison(TerminatorInst *TI) {
- if (SwitchInst *SI = dyn_cast<SwitchInst>(TI))
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ // Do not permit merging of large switch instructions into their
+ // predecessors unless there is only one predecessor.
+ if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
+ pred_end(SI->getParent())) > 128)
+ return 0;
+
return SI->getCondition();
+ }
if (BranchInst *BI = dyn_cast<BranchInst>(TI))
if (BI->isConditional() && BI->getCondition()->hasOneUse())
if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))