1 files changed, 45 insertions, 8 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 7fc018556e1..0df2971b104 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1760,6 +1760,18 @@ bool CodeGenPrepare::optimizeCallInst(CallInst *CI, bool& ModifiedDT) {
     }
   }
 
+  // If we have a cold call site, try to sink addressing computation into the
+  // cold block.  This interacts with our handling for loads and stores to
+  // ensure that we can fold all uses of a potential addressing computation
+  // into their uses.  TODO: generalize this to work over profiling data
+  if (!OptSize && CI->hasFnAttr(Attribute::Cold))
+    for (auto &Arg : CI->arg_operands()) {
+      if (!Arg->getType()->isPointerTy())
+        continue;
+      unsigned AS = Arg->getType()->getPointerAddressSpace();
+      return optimizeMemoryInst(CI, Arg, Arg->getType(), AS);
+    }
+  
   IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI);
   if (II) {
     switch (II->getIntrinsicID()) {
@@ -3443,6 +3455,8 @@ static bool FindAllMemoryUses(
   if (!MightBeFoldableInst(I))
     return true;
 
+  const bool OptSize = I->getFunction()->optForSize();
+
   // Loop over all the uses, recursively processing them.
   for (Use &U : I->uses()) {
     Instruction *UserI = cast<Instruction>(U.getUser());
@@ -3460,6 +3474,11 @@ static bool FindAllMemoryUses(
     }
 
     if (CallInst *CI = dyn_cast<CallInst>(UserI)) {
+      // If this is a cold call, we can sink the addressing calculation into
+      // the cold path.  See optimizeCallInst
+      if (!OptSize && CI->hasFnAttr(Attribute::Cold))
+        continue;
+      
       InlineAsm *IA = dyn_cast<InlineAsm>(CI->getCalledValue());
       if (!IA) return true;
 
@@ -3551,10 +3570,10 @@ isProfitableToFoldIntoAddressingMode(Instruction *I, ExtAddrMode &AMBefore,
   if (!BaseReg && !ScaledReg)
     return true;
 
-  // If all uses of this instruction are ultimately load/store/inlineasm's,
-  // check to see if their addressing modes will include this instruction.  If
-  // so, we can fold it into all uses, so it doesn't matter if it has multiple
-  // uses.
+  // If all uses of this instruction can have the address mode sunk into them,
+  // we can remove the addressing mode and effectively trade one live register
+  // for another (at worst.)  In this context, folding an addressing mode into
+  // the use is just a particularly nice way of sinking it.  
   SmallVector<std::pair<Instruction*,unsigned>, 16> MemoryUses;
   SmallPtrSet<Instruction*, 16> ConsideredInsts;
   if (FindAllMemoryUses(I, MemoryUses, ConsideredInsts, TM))
@@ -3562,8 +3581,13 @@ isProfitableToFoldIntoAddressingMode(Instruction *I, ExtAddrMode &AMBefore,
 
   // Now that we know that all uses of this instruction are part of a chain of
   // computation involving only operations that could theoretically be folded
-  // into a memory use, loop over each of these uses and see if they could
-  // *actually* fold the instruction.
+  // into a memory use, loop over each of these memory operation uses and see
+  // if they could  *actually* fold the instruction.  The assumption is that
+  // addressing modes are cheap and that duplicating the computation involved
+  // many times is worthwhile, even on a fastpath. For sinking candidates
+  // (i.e. cold call sites), this serves as a way to prevent excessive code
+  // growth since most architectures have some reasonable small and fast way to
+  // compute an effective address.  (i.e LEA on x86)
   SmallVector<Instruction*, 32> MatchedAddrModeInsts;
   for (unsigned i = 0, e = MemoryUses.size(); i != e; ++i) {
     Instruction *User = MemoryUses[i].first;
@@ -3617,6 +3641,11 @@ static bool IsNonLocalValue(Value *V, BasicBlock *BB) {
   return false;
 }
 
+/// Sink addressing mode computation immediate before MemoryInst if doing so
+/// can be done without increasing register pressure.  The need for the
+/// register pressure constraint means this can end up being an all or nothing
+/// decision for all uses of the same addressing computation.
+///
 /// Load and Store Instructions often have addressing modes that can do
 /// significant amounts of computation. As such, instruction selection will try
 /// to get the load or store to do as much computation as possible for the
@@ -3624,7 +3653,13 @@ static bool IsNonLocalValue(Value *V, BasicBlock *BB) {
 /// such, we sink as much legal addressing mode work into the block as possible.
 ///
 /// This method is used to optimize both load/store and inline asms with memory
-/// operands.
+/// operands.  It's also used to sink addressing computations feeding into cold
+/// call sites into their (cold) basic block.
+///
+/// The motivation for handling sinking into cold blocks is that doing so can
+/// both enable other address mode sinking (by satisfying the register pressure
+/// constraint above), and reduce register pressure globally (by removing the
+/// addressing mode computation from the fast path entirely.).
 bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
                                         Type *AccessTy, unsigned AddrSpace) {
   Value *Repl = Addr;
@@ -3663,7 +3698,9 @@ bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
       continue;
     }
 
-    // For non-PHIs, determine the addressing mode being computed.
+    // For non-PHIs, determine the addressing mode being computed.  Note that
+    // the result may differ depending on what other uses our candidate
+    // addressing instructions might have.
     SmallVector<Instruction*, 16> NewAddrModeInsts;
     ExtAddrMode NewAddrMode = AddressingModeMatcher::Match(
       V, AccessTy, AddrSpace, MemoryInst, NewAddrModeInsts, *TM,