X86 Peephole: fold loads to the source register operand if possible.

Machine CSE and other optimizations can remove instructions so folding
is possible at peephole while not possible at ISel.

rdar://10554090 and rdar://11873276


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160919 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 0 deletions

diff --git a/lib/CodeGen/PeepholeOptimizer.cpp b/lib/CodeGen/PeepholeOptimizer.cpp
index 91c33c4..0a4632a 100644
--- a/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/lib/CodeGen/PeepholeOptimizer.cpp
@@ -78,6 +78,7 @@ STATISTIC(NumReuse,      "Number of extension results reused");
 STATISTIC(NumBitcasts,   "Number of bitcasts eliminated");
 STATISTIC(NumCmps,       "Number of compares eliminated");
 STATISTIC(NumImmFold,    "Number of move immediate folded");
+STATISTIC(NumLoadFold,   "Number of loads folded");
 
 namespace {
   class PeepholeOptimizer : public MachineFunctionPass {
@@ -441,6 +442,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
   SmallPtrSet<MachineInstr*, 8> LocalMIs;
   SmallSet<unsigned, 4> ImmDefRegs;
   DenseMap<unsigned, MachineInstr*> ImmDefMIs;
+  SmallSet<unsigned, 4> FoldAsLoadDefRegs;
   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
     MachineBasicBlock *MBB = &*I;
 
@@ -448,6 +450,7 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
     LocalMIs.clear();
     ImmDefRegs.clear();
     ImmDefMIs.clear();
+    FoldAsLoadDefRegs.clear();
 
     bool First = true;
     MachineBasicBlock::iterator PMII;
@@ -489,6 +492,25 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
           Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs);
       }
 
+      MachineInstr *DefMI = 0;
+      MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI, FoldAsLoadDefRegs,
+                                                    DefMI);
+      if (FoldMI) {
+        // Update LocalMIs since we replaced MI with FoldMI and deleted DefMI.
+        LocalMIs.erase(MI);
+        LocalMIs.erase(DefMI);
+        LocalMIs.insert(FoldMI);
+        MI->eraseFromParent();
+        DefMI->eraseFromParent();
+        ++NumLoadFold;
+
+        // MI is replaced with FoldMI.
+        Changed = true;
+        PMII = FoldMI;
+        MII = llvm::next(PMII);
+        continue;
+      }
+
       First = false;
       PMII = MII;
       ++MII;