1 files changed, 39 insertions, 19 deletions

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 66c5aa5ff784..baea9642d4fd 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -18,6 +18,7 @@
 
 #define DEBUG_TYPE "branchfolding"
 #include "BranchFolding.h"
+#include "llvm/Function.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
@@ -444,6 +445,36 @@ static bool MergeCompare(const std::pair<unsigned,MachineBasicBlock*> &p,
     }
 }
 
+/// ProfitableToMerge - Check if two machine basic blocks have a common tail
+/// and decide if it would be profitable to merge those tails.  Return the
+/// length of the common tail and iterators to the first common instruction
+/// in each block.
+static bool ProfitableToMerge(MachineBasicBlock *MBB1,
+                              MachineBasicBlock *MBB2,
+                              unsigned minCommonTailLength,
+                              unsigned &CommonTailLen,
+                              MachineBasicBlock::iterator &I1,
+                              MachineBasicBlock::iterator &I2) {
+  CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2);
+  MachineFunction *MF = MBB1->getParent();
+
+  if (CommonTailLen >= minCommonTailLength)
+    return true;
+
+  if (CommonTailLen == 0)
+    return false;
+
+  // If we are optimizing for code size, 1 instruction in common is enough if
+  // we don't have to split a block.  At worst we will be replacing a
+  // fallthrough into the common tail with a branch, which at worst breaks
+  // even with falling through into the duplicated common tail.
+  if (MF->getFunction()->hasFnAttr(Attribute::OptimizeForSize) &&
+      (I1 == MBB1->begin() || I2 == MBB2->begin()))
+    return true;
+
+  return false;
+}
+
 /// ComputeSameTails - Look through all the blocks in MergePotentials that have
 /// hash CurHash (guaranteed to match the last element).   Build the vector 
 /// SameTails of all those that have the (same) largest number of instructions
@@ -465,22 +496,9 @@ unsigned BranchFolder::ComputeSameTails(unsigned CurHash,
        CurMPIter!=B && CurMPIter->first==CurHash;
        --CurMPIter) {
     for (MPIterator I = prior(CurMPIter); I->first==CurHash ; --I) {
-      unsigned CommonTailLen = ComputeCommonTailLength(
-                                        CurMPIter->second,
-                                        I->second,
-                                        TrialBBI1, TrialBBI2);
-      // If we will have to split a block, there should be at least
-      // minCommonTailLength instructions in common; if not, at worst
-      // we will be replacing a fallthrough into the common tail with a
-      // branch, which at worst breaks even with falling through into
-      // the duplicated common tail, so 1 instruction in common is enough.
-      // We will always pick a block we do not have to split as the common
-      // tail if there is one.
-      // (Empty blocks will get forwarded and need not be considered.)
-      if (CommonTailLen >= minCommonTailLength ||
-          (CommonTailLen > 0 &&
-           (TrialBBI1==CurMPIter->second->begin() ||
-            TrialBBI2==I->second->begin()))) {
+      unsigned CommonTailLen;
+      if (ProfitableToMerge(CurMPIter->second, I->second, minCommonTailLength,
+                            CommonTailLen, TrialBBI1, TrialBBI2)) {
         if (CommonTailLen > maxCommonTailLength) {
           SameTails.clear();
           maxCommonTailLength = CommonTailLen;
@@ -863,8 +881,9 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
   
   // If this block is empty, make everyone use its fall-through, not the block
   // explicitly.  Landing pads should not do this since the landing-pad table
-  // points to this block.
-  if (MBB->empty() && !MBB->isLandingPad()) {
+  // points to this block.  Blocks with their addresses taken shouldn't be
+  // optimized away.
+  if (MBB->empty() && !MBB->isLandingPad() && !MBB->hasAddressTaken()) {
     // Dead block?  Leave for cleanup later.
     if (MBB->pred_empty()) return MadeChange;
     
@@ -1031,7 +1050,8 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
     // If this branch is the only thing in its block, see if we can forward
     // other blocks across it.
     if (CurTBB && CurCond.empty() && CurFBB == 0 && 
-        MBB->begin()->getDesc().isBranch() && CurTBB != MBB) {
+        MBB->begin()->getDesc().isBranch() && CurTBB != MBB &&
+        !MBB->hasAddressTaken()) {
       // This block may contain just an unconditional branch.  Because there can
       // be 'non-branch terminators' in the block, try removing the branch and
       // then seeing if the block is empty.