From c0d025f54f96ff719ae99d57d7c413aee35b6cbc Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sun, 9 Mar 2008 04:55:16 +0000
Subject: [PATCH] Prune the unwind_to labels on BBs that don't need them.
 Another step in the removal of invoke, PR1269.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48084 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/IPO/PruneEH.cpp      | 19 ++++++++++++++++---
 test/Transforms/PruneEH/unwindto.ll | 15 +++++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)
 create mode 100644 test/Transforms/PruneEH/unwindto.ll

diff --git a/lib/Transforms/IPO/PruneEH.cpp b/lib/Transforms/IPO/PruneEH.cpp
index 4e621dc2f93..fa8b95a2ade 100644
--- a/lib/Transforms/IPO/PruneEH.cpp
+++ b/lib/Transforms/IPO/PruneEH.cpp
@@ -32,6 +32,7 @@ using namespace llvm;
 
 STATISTIC(NumRemoved, "Number of invokes removed");
 STATISTIC(NumUnreach, "Number of noreturn calls optimized");
+STATISTIC(NumBBUnwind, "Number of unwind_to removed from blocks");
 
 namespace {
   struct VISIBILITY_HIDDEN PruneEH : public CallGraphSCCPass {
@@ -153,6 +154,8 @@ bool PruneEH::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
 bool PruneEH::SimplifyFunction(Function *F) {
   bool MadeChange = false;
   for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
+    bool couldUnwind = false;
+
     if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
       if (II->doesNotThrow()) {
         SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
@@ -182,10 +185,11 @@ bool PruneEH::SimplifyFunction(Function *F) {
 
         ++NumRemoved;
         MadeChange = true;
-      }
+      } else
+        couldUnwind = true;
 
     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; )
-      if (CallInst *CI = dyn_cast<CallInst>(I++))
+      if (CallInst *CI = dyn_cast<CallInst>(I++)) {
         if (CI->doesNotReturn() && !isa<UnreachableInst>(I)) {
           // This call calls a function that cannot return.  Insert an
           // unreachable instruction after it and simplify the code.  Do this
@@ -201,8 +205,17 @@ bool PruneEH::SimplifyFunction(Function *F) {
           MadeChange = true;
           ++NumUnreach;
           break;
-        }
+        } else if (!CI->doesNotThrow())
+          couldUnwind = true;
+      }
 
+    // Strip 'unwindTo' off of BBs that have no calls/invokes without nounwind.
+    if (!couldUnwind && BB->getUnwindDest()) {
+      MadeChange = true;
+      ++NumBBUnwind;
+      BB->getUnwindDest()->removePredecessor(BB, false, true);
+      BB->setUnwindDest(NULL);
+    }
   }
   return MadeChange;
 }
diff --git a/test/Transforms/PruneEH/unwindto.ll b/test/Transforms/PruneEH/unwindto.ll
new file mode 100644
index 00000000000..8e5ac25ec86
--- /dev/null
+++ b/test/Transforms/PruneEH/unwindto.ll
@@ -0,0 +1,15 @@
+; RUN: llvm-as < %s | opt -prune-eh | llvm-dis | not grep unwind_to
+
+define i8 @test7(i1 %b) {
+entry: unwind_to %cleanup
+  br i1 %b, label %cond_true, label %cond_false
+cond_true: unwind_to %cleanup
+  br label %cleanup
+cond_false: unwind_to %cleanup
+  br label %cleanup
+cleanup:
+  %x = phi i8 [0, %entry], [1, %cond_true], [1, %cond_true],
+                           [2, %cond_false], [2, %cond_false]
+  ret i8 %x
+}
+
-- 
2.11.0