Implement PR1786 by iterating between dead cycle elimination
and simplifycfg in the rare cases when it is needed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44044 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/SimplifyCFG.cpp b/lib/Transforms/Scalar/SimplifyCFG.cpp
index 5f0ab19..200264e 100644
--- a/lib/Transforms/Scalar/SimplifyCFG.cpp
+++ b/lib/Transforms/Scalar/SimplifyCFG.cpp
@@ -27,6 +27,7 @@
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Pass.h"
+#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
@@ -50,9 +51,9 @@
}
static bool MarkAliveBlocks(BasicBlock *BB,
- SmallPtrSet<BasicBlock*, 16> &Reachable) {
+ SmallPtrSet<BasicBlock*, 128> &Reachable) {
- std::vector<BasicBlock*> Worklist;
+ SmallVector<BasicBlock*, 128> Worklist;
Worklist.push_back(BB);
bool Changed = false;
while (!Worklist.empty()) {
@@ -93,42 +94,46 @@
return Changed;
}
-
-// It is possible that we may require multiple passes over the code to fully
-// simplify the CFG.
-//
-bool CFGSimplifyPass::runOnFunction(Function &F) {
- SmallPtrSet<BasicBlock*, 16> Reachable;
+/// RemoveUnreachableBlocks - Remove blocks that are not reachable, even if they
+/// are in a dead cycle. Return true if a change was made, false otherwise.
+static bool RemoveUnreachableBlocks(Function &F) {
+ SmallPtrSet<BasicBlock*, 128> Reachable;
bool Changed = MarkAliveBlocks(F.begin(), Reachable);
-
+
// If there are unreachable blocks in the CFG...
- if (Reachable.size() != F.size()) {
- assert(Reachable.size() < F.size());
- NumSimpl += F.size()-Reachable.size();
+ if (Reachable.size() == F.size())
+ return Changed;
+
+ assert(Reachable.size() < F.size());
+ NumSimpl += F.size()-Reachable.size();
+
+ // Loop over all of the basic blocks that are not reachable, dropping all of
+ // their internal references...
+ for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB)
+ if (!Reachable.count(BB)) {
+ for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI!=SE; ++SI)
+ if (Reachable.count(*SI))
+ (*SI)->removePredecessor(BB);
+ BB->dropAllReferences();
+ }
+
+ for (Function::iterator I = ++F.begin(); I != F.end();)
+ if (!Reachable.count(I))
+ I = F.getBasicBlockList().erase(I);
+ else
+ ++I;
+
+ return true;
+}
- // Loop over all of the basic blocks that are not reachable, dropping all of
- // their internal references...
- for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB)
- if (!Reachable.count(BB)) {
- for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI!=SE; ++SI)
- if (Reachable.count(*SI))
- (*SI)->removePredecessor(BB);
- BB->dropAllReferences();
- }
-
- for (Function::iterator I = ++F.begin(); I != F.end();)
- if (!Reachable.count(I))
- I = F.getBasicBlockList().erase(I);
- else
- ++I;
-
- Changed = true;
- }
-
+/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
+/// iterating until no more changes are made.
+static bool IterativeSimplifyCFG(Function &F) {
+ bool Changed = false;
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
-
+
// Loop over all of the basic blocks (except the first one) and remove them
// if they are unneeded...
//
@@ -140,6 +145,31 @@
}
Changed |= LocalChange;
}
-
return Changed;
}
+
+// It is possible that we may require multiple passes over the code to fully
+// simplify the CFG.
+//
+bool CFGSimplifyPass::runOnFunction(Function &F) {
+ bool EverChanged = RemoveUnreachableBlocks(F);
+ EverChanged |= IterativeSimplifyCFG(F);
+
+ // If neither pass changed anything, we're done.
+ if (!EverChanged) return false;
+
+ // IterativeSimplifyCFG can (rarely) make some loops dead. If this happens,
+ // RemoveUnreachableBlocks is needed to nuke them, which means we should
+ // iterate between the two optimizations. We structure the code like this to
+ // avoid reruning IterativeSimplifyCFG if the second pass of
+ // RemoveUnreachableBlocks doesn't do anything.
+ if (!RemoveUnreachableBlocks(F))
+ return true;
+
+ do {
+ EverChanged = IterativeSimplifyCFG(F);
+ EverChanged |= RemoveUnreachableBlocks(F);
+ } while (EverChanged);
+
+ return true;
+}