Enable aggressive hoisting when optimizing for code-size.

[sebpop]

LGTM. Thanks.

lib/Transforms/Scalar/GVNHoist.cpp

 // This pass hoists common computations across branches sharing common
 // dominator. The primary goal is to reduce the code size, and in some
 // cases reduce critical path (by exposing more ILP).
 class GVNHoist {
 public:
   GVNHoist(DominatorTree *DT, AliasAnalysis *AA, MemoryDependenceResults *MD,
            MemorySSA *MSSA, bool OptForMinSize)
       : DT(DT), AA(AA), MD(MD), MSSA(MSSA), OptForMinSize(OptForMinSize),
-        HoistingGeps(OptForMinSize), HoistedCtr(0) {}
+        HoistingGeps(OptForMinSize), HoistedCtr(0) {
+      // Hoist as far as possible when optimizing for code-size.
+      if (OptForMinSize)
+        MaxNumberOfBBSInPath = -1;
+  }
+
   bool run(Function &F) {
     VN.setDomTree(DT);
     VN.setAliasAnalysis(AA);
     VN.setMemDep(MD);
     bool Res = false;
     // Perform DFS Numbering of instructions.
     unsigned BBI = 0;
     for (const BasicBlock *BB : depth_first(&F.getEntryBlock())) {
bool safeToHoistLdSt(const Instruction *NewPt, const Instruction *OldPt,
     return true;
   }
 
   // Return true when it is safe to hoist scalar instructions from all blocks in
   // WL to HoistBB.
   bool safeToHoistScalar(const BasicBlock *HoistBB,
                          SmallPtrSetImpl<const BasicBlock *> &WL,
                          int &NBBsOnAllPaths) {
-    // Check that the hoisted expression is needed on all paths.  Enable scalar
-    // hoisting at -Oz as it is safe to hoist scalars to a place where they are
-    // partially needed.
-    if (!OptForMinSize && !hoistingFromAllPaths(HoistBB, WL))
+    // Enable scalar hoisting at -Oz as it is safe to hoist scalars to a place
+    // where they are partially needed.
+    if (OptForMinSize)
+      return true;
+
+    // Check that the hoisted expression is needed on all paths.
+    if (!hoistingFromAllPaths(HoistBB, WL))
       return false;
 
     for (const BasicBlock *BB : WL)
       if (hasEHOnPath(HoistBB, BB, NBBsOnAllPaths))
         return false;
 
     return true;
   }