Checkin an improvement contributed by Bill:

Only transform call sites in a setjmp'ing function which are reachable from
the setjmp.  If the call dominates the setjmp (for example), the called
function cannot longjmp to the setjmp.

This dramatically reduces the number of invoke instructions created in some
large testcases.

llvm-svn: 9066

llvm/lib/Transforms/IPO/LowerSetJmp.cpp

@@ -32,14 +32,13 @@
 #include "llvm/Intrinsics.h"
 #include "llvm/Module.h"
 #include "llvm/Pass.h"
-#include "llvm/Support/InstIterator.h"
+#include "llvm/Support/CFG.h"
 #include "llvm/Support/InstVisitor.h"
+#include "Support/DepthFirstIterator.h"
 #include "Support/Statistic.h"
 #include "Support/StringExtras.h"
 #include "Support/VectorExtras.h"
 
-#include <set>
-
 namespace {
   Statistic<> LongJmpsTransformed("lowersetjmp",
                                   "Number of longjmps transformed");
@@ -64,6 +63,11 @@ namespace {
 
     typedef std::pair<SwitchInst*, CallInst*> SwitchValuePair;
 
+    // Keep track of those basic blocks reachable via a depth-first search of
+    // the CFG from a setjmp call. We only need to transform those "call" and
+    // "invoke" instructions that are reachable from the setjmp call site.
+    std::set<BasicBlock*> DFSBlocks;
+
     // The setjmp map is going to hold information about which setjmps
     // were called (each setjmp gets its own number) and with which
     // buffer it was called.
@@ -127,13 +131,24 @@ bool LowerSetJmp::run(Module& M)
   // setjmp/longjmp functions.
   doInitialization(M);
 
-  if (SetJmp)
+  if (SetJmp) {
+    std::set<BasicBlock*> BBSet;
+    
+    for (Value::use_iterator B = SetJmp->use_begin(), E = SetJmp->use_end();
+         B != E; ++B) {
+      Instruction* I = cast<Instruction>(*B);
+      BasicBlock* BB = I->getParent();
+      Function* Func = BB->getParent();
+      DFSBlocks.insert(df_begin(BB), df_end(BB));
+    }
+
     while (!SetJmp->use_empty()) {
       assert(isa<CallInst>(SetJmp->use_back()) &&
              "User of setjmp intrinsic not a call?");
       TransformSetJmpCall(cast<CallInst>(SetJmp->use_back()));
       Changed = true;
     }
+  }
 
   if (LongJmp)
     while (!LongJmp->use_empty()) {
@@ -156,6 +171,7 @@ bool LowerSetJmp::run(Module& M)
       }
   }
 
+  DFSBlocks.clear();
   SJMap.clear();
   RethrowBBMap.clear();
   PrelimBBMap.clear();
@@ -398,12 +414,16 @@ void LowerSetJmp::visitCallInst(CallInst& CI)
         CI.getCalledFunction()->isIntrinsic()) return;
 
   BasicBlock* OldBB = CI.getParent();
+  Function* Func = OldBB->getParent();
+
+  // If not reachable from a setjmp call, don't transform.
+  if (!DFSBlocks.count(OldBB)) return;
+
   BasicBlock* NewBB = OldBB->splitBasicBlock(CI);
   assert(NewBB && "Couldn't split BB of \"call\" instruction!!");
   NewBB->setName("Call2Invoke");
 
   // Reposition the split BB in the BB list to make things tidier.
-  Function* Func = OldBB->getParent();
   Func->getBasicBlockList().remove(NewBB);
   Func->getBasicBlockList().insert(++Function::iterator(OldBB), NewBB);
 
@@ -432,7 +452,11 @@ void LowerSetJmp::visitInvokeInst(InvokeInst& II)
     if (!IsTransformableFunction(II.getCalledFunction()->getName()) ||
         II.getCalledFunction()->isIntrinsic()) return;
 
-  Function* Func = II.getParent()->getParent();
+  BasicBlock* BB = II.getParent();
+  Function* Func = BB->getParent();
+
+  // If not reachable from a setjmp call, don't transform.
+  if (!DFSBlocks.count(BB)) return;
 
   BasicBlock* NormalBB = II.getNormalDest();
   BasicBlock* ExceptBB = II.getExceptionalDest();