Vendor import of llvm trunk r130700:

http://llvm.org/svn/llvm-project/llvm/trunk@130700

1 files changed, 97 insertions, 4 deletions

diff --git a/lib/CodeGen/PeepholeOptimizer.cpp b/lib/CodeGen/PeepholeOptimizer.cpp
index 5d7123c..c105bb0 100644
--- a/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/lib/CodeGen/PeepholeOptimizer.cpp
@@ -30,6 +30,15 @@
 //     If the "sub" instruction all ready sets (or could be modified to set) the
 //     same flag that the "cmp" instruction sets and that "bz" uses, then we can
 //     eliminate the "cmp" instruction.
+//
+// - Optimize Bitcast pairs:
+//
+//     v1 = bitcast v0
+//     v2 = bitcast v1
+//        = v2
+//   =>
+//     v1 = bitcast v0
+//        = v0
 // 
 //===----------------------------------------------------------------------===//
 
@@ -57,7 +66,8 @@ DisablePeephole("disable-peephole", cl::Hidden, cl::init(false),
                 cl::desc("Disable the peephole optimizer"));
 
 STATISTIC(NumReuse,      "Number of extension results reused");
-STATISTIC(NumEliminated, "Number of compares eliminated");
+STATISTIC(NumBitcasts,   "Number of bitcasts eliminated");
+STATISTIC(NumCmps,       "Number of compares eliminated");
 STATISTIC(NumImmFold,    "Number of move immediate foled");
 
 namespace {
@@ -85,6 +95,7 @@ namespace {
     }
 
   private:
+    bool OptimizeBitcastInstr(MachineInstr *MI, MachineBasicBlock *MBB);
     bool OptimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB);
     bool OptimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
                           SmallPtrSet<MachineInstr*, 8> &LocalMIs);
@@ -243,12 +254,85 @@ OptimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
   return Changed;
 }
 
+/// OptimizeBitcastInstr - If the instruction is a bitcast instruction A that
+/// cannot be optimized away during isel (e.g. ARM::VMOVSR, which bitcast
+/// a value cross register classes), and the source is defined by another
+/// bitcast instruction B. And if the register class of source of B matches
+/// the register class of instruction A, then it is legal to replace all uses
+/// of the def of A with source of B. e.g.
+///   %vreg0<def> = VMOVSR %vreg1
+///   %vreg3<def> = VMOVRS %vreg0
+///   Replace all uses of vreg3 with vreg1.
+
+bool PeepholeOptimizer::OptimizeBitcastInstr(MachineInstr *MI,
+                                             MachineBasicBlock *MBB) {
+  unsigned NumDefs = MI->getDesc().getNumDefs();
+  unsigned NumSrcs = MI->getDesc().getNumOperands() - NumDefs;
+  if (NumDefs != 1)
+    return false;
+
+  unsigned Def = 0;
+  unsigned Src = 0;
+  for (unsigned i = 0, e = NumDefs + NumSrcs; i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg())
+      continue;
+    unsigned Reg = MO.getReg();
+    if (!Reg)
+      continue;
+    if (MO.isDef())
+      Def = Reg;
+    else if (Src)
+      // Multiple sources?
+      return false;
+    else
+      Src = Reg;
+  }
+
+  assert(Def && Src && "Malformed bitcast instruction!");
+
+  MachineInstr *DefMI = MRI->getVRegDef(Src);
+  if (!DefMI || !DefMI->getDesc().isBitcast())
+    return false;
+
+  unsigned SrcDef = 0;
+  unsigned SrcSrc = 0;
+  NumDefs = DefMI->getDesc().getNumDefs();
+  NumSrcs = DefMI->getDesc().getNumOperands() - NumDefs;
+  if (NumDefs != 1)
+    return false;
+  for (unsigned i = 0, e = NumDefs + NumSrcs; i != e; ++i) {
+    const MachineOperand &MO = DefMI->getOperand(i);
+    if (!MO.isReg() || MO.isDef())
+      continue;
+    unsigned Reg = MO.getReg();
+    if (!Reg)
+      continue;
+    if (MO.isDef())
+      SrcDef = Reg;
+    else if (SrcSrc)
+      // Multiple sources?
+      return false;
+    else
+      SrcSrc = Reg;
+  }
+
+  if (MRI->getRegClass(SrcSrc) != MRI->getRegClass(Def))
+    return false;
+
+  MRI->replaceRegWith(Def, SrcSrc);
+  MRI->clearKillFlags(SrcSrc);
+  MI->eraseFromParent();
+  ++NumBitcasts;
+  return true;
+}
+
 /// OptimizeCmpInstr - If the instruction is a compare and the previous
 /// instruction it's comparing against all ready sets (or could be modified to
 /// set) the same flag as the compare, then we can remove the comparison and use
 /// the flag from the previous instruction.
 bool PeepholeOptimizer::OptimizeCmpInstr(MachineInstr *MI,
-                                         MachineBasicBlock *MBB){
+                                         MachineBasicBlock *MBB) {
   // If this instruction is a comparison against zero and isn't comparing a
   // physical register, we can try to optimize it.
   unsigned SrcReg;
@@ -259,7 +343,7 @@ bool PeepholeOptimizer::OptimizeCmpInstr(MachineInstr *MI,
 
   // Attempt to optimize the comparison instruction.
   if (TII->OptimizeCompareInstr(MI, SrcReg, CmpMask, CmpValue, MRI)) {
-    ++NumEliminated;
+    ++NumCmps;
     return true;
   }
 
@@ -345,7 +429,16 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
         continue;
       }
 
-      if (MI->getDesc().isCompare()) {
+      const TargetInstrDesc &TID = MI->getDesc();
+
+      if (TID.isBitcast()) {
+        if (OptimizeBitcastInstr(MI, MBB)) {
+          // MI is deleted.
+          Changed = true;
+          MII = First ? I->begin() : llvm::next(PMII);
+          continue;
+        }        
+      } else if (TID.isCompare()) {
         if (OptimizeCmpInstr(MI, MBB)) {
           // MI is deleted.
           Changed = true;