Improve ValueAlreadyLiveAtInst with a cheap and dirty, but effective

heuristic: the value is already live at the new memory operation if
it is used by some other instruction in the memop's block.  This is
cheap and simple to compute (moreso than full liveness).

This improves the new heuristic even more.  For example, it cuts two
out of three new instructions out of 255.vortex:DbmFileInGrpHdr,
which is one of the functions that the heuristic regressed.  This
overall eliminates another 40 instructions from 403.gcc and visibly
reduces register pressure in 255.vortex (though this only actually
ends up saving the 2 instructions from the whole program).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60084 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index 4c51fe7102643c4cc490cc0ded04f89aa13f0c51..f09a7e42262788e3f2eb15a7c2ce7f21a3aa31d0 100644 (file)
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -539,7 +539,14 @@ namespace {
 class AddressingModeMatcher {
   SmallVectorImpl<Instruction*> &AddrModeInsts;
   const TargetLowering &TLI;
+
+  /// AccessTy/MemoryInst - This is the type for the access (e.g. double) and
+  /// the memory instruction that we're computing this address for.
   const Type *AccessTy;
+  Instruction *MemoryInst;
+  
+  /// AddrMode - This is the addressing mode that we're building up.  This is
+  /// part of the return value of this addressing mode matching stuff.
   ExtAddrMode &AddrMode;
   
   /// IgnoreProfitability - This is set to true when we should not do
@@ -548,8 +555,9 @@ class AddressingModeMatcher {
   bool IgnoreProfitability;
   
   AddressingModeMatcher(SmallVectorImpl<Instruction*> &AMI,
-                        const TargetLowering &T, const Type *AT,ExtAddrMode &AM)
-    : AddrModeInsts(AMI), TLI(T), AccessTy(AT), AddrMode(AM) {
+                        const TargetLowering &T, const Type *AT,
+                        Instruction *MI, ExtAddrMode &AM)
+    : AddrModeInsts(AMI), TLI(T), AccessTy(AT), MemoryInst(MI), AddrMode(AM) {
     IgnoreProfitability = false;
   }
 public:
@@ -557,13 +565,15 @@ public:
   /// Match - Find the maximal addressing mode that a load/store of V can fold,
   /// give an access type of AccessTy.  This returns a list of involved
   /// instructions in AddrModeInsts.
-  static ExtAddrMode Match(Value *V, const Type *AccessTy, 
+  static ExtAddrMode Match(Value *V, const Type *AccessTy,
+                           Instruction *MemoryInst,
                            SmallVectorImpl<Instruction*> &AddrModeInsts,
                            const TargetLowering &TLI) {
     ExtAddrMode Result;
 
     bool Success = 
-      AddressingModeMatcher(AddrModeInsts,TLI,AccessTy,Result).MatchAddr(V, 0);
+      AddressingModeMatcher(AddrModeInsts, TLI, AccessTy,
+                            MemoryInst, Result).MatchAddr(V, 0);
     Success = Success; assert(Success && "Couldn't select *anything*?");
     return Result;
   }
@@ -945,7 +955,7 @@ bool AddressingModeMatcher::ValueAlreadyLiveAtInst(Value *Val,Value *KnownLive1,
   if (Val == 0 || Val == KnownLive1 || Val == KnownLive2)
     return true;
   
-  // All non-instruction values other than arguments (constants) are live.
+  // All values other than instructions and arguments (e.g. constants) are live.
   if (!isa<Instruction>(Val) && !isa<Argument>(Val)) return true;
   
   // If Val is a constant sized alloca in the entry block, it is live, this is
@@ -955,6 +965,16 @@ bool AddressingModeMatcher::ValueAlreadyLiveAtInst(Value *Val,Value *KnownLive1,
     if (AI->isStaticAlloca())
       return true;
   
+  // Check to see if this value is already used in the memory instruction's
+  // block.  If so, it's already live into the block at the very least, so we
+  // can reasonably fold it.
+  BasicBlock *MemBB = MemoryInst->getParent();
+  for (Value::use_iterator UI = Val->use_begin(), E = Val->use_end();
+       UI != E; ++UI)
+    // We know that uses of arguments and instructions have to be instructions.
+    if (cast<Instruction>(*UI)->getParent() == MemBB)
+      return true;
+  
   return false;
 }
 
@@ -1044,7 +1064,7 @@ IsProfitableToFoldIntoAddressingMode(Instruction *I, ExtAddrMode &AMBefore,
     // *actually* cover the shared instruction.
     ExtAddrMode Result;
     AddressingModeMatcher Matcher(MatchedAddrModeInsts, TLI, AddressAccessTy,
-                                  Result);
+                                  MemoryInst, Result);
     Matcher.IgnoreProfitability = true;
     bool Success = Matcher.MatchAddr(Address, 0);
     Success = Success; assert(Success && "Couldn't select *anything*?");
@@ -1082,19 +1102,19 @@ static bool IsNonLocalValue(Value *V, BasicBlock *BB) {
 ///
 /// This method is used to optimize both load/store and inline asms with memory
 /// operands.
-bool CodeGenPrepare::OptimizeMemoryInst(Instruction *LdStInst, Value *Addr,
+bool CodeGenPrepare::OptimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
                                         const Type *AccessTy,
                                         DenseMap<Value*,Value*> &SunkAddrs) {
   // Figure out what addressing mode will be built up for this operation.
   SmallVector<Instruction*, 16> AddrModeInsts;
-  ExtAddrMode AddrMode = 
-    AddressingModeMatcher::Match(Addr, AccessTy, AddrModeInsts, *TLI);
+  ExtAddrMode AddrMode = AddressingModeMatcher::Match(Addr, AccessTy,MemoryInst,
+                                                      AddrModeInsts, *TLI);
 
   // Check to see if any of the instructions supersumed by this addr mode are
   // non-local to I's BB.
   bool AnyNonLocal = false;
   for (unsigned i = 0, e = AddrModeInsts.size(); i != e; ++i) {
-    if (IsNonLocalValue(AddrModeInsts[i], LdStInst->getParent())) {
+    if (IsNonLocalValue(AddrModeInsts[i], MemoryInst->getParent())) {
       AnyNonLocal = true;
       break;
     }
@@ -1109,7 +1129,7 @@ bool CodeGenPrepare::OptimizeMemoryInst(Instruction *LdStInst, Value *Addr,
   // Insert this computation right after this user.  Since our caller is
   // scanning from the top of the BB to the bottom, reuse of the expr are
   // guaranteed to happen later.
-  BasicBlock::iterator InsertPt = LdStInst;
+  BasicBlock::iterator InsertPt = MemoryInst;
 
   // Now that we determined the addressing expression we want to use and know
   // that we have to sink it into this block.  Check to see if we have already
@@ -1181,7 +1201,7 @@ bool CodeGenPrepare::OptimizeMemoryInst(Instruction *LdStInst, Value *Addr,
       SunkAddr = new IntToPtrInst(Result, Addr->getType(), "sunkaddr",InsertPt);
   }
 
-  LdStInst->replaceUsesOfWith(Addr, SunkAddr);
+  MemoryInst->replaceUsesOfWith(Addr, SunkAddr);
 
   if (Addr->use_empty())
     EraseDeadInstructions(Addr);