Replace TargetInstrInfo::isInvariantLoad and its target-specific

implementations with a new MachineInstr::isInvariantLoad, which uses
MachineMemOperands and is target-independent. This brings MachineLICM
and other functionality to targets which previously lacked an
isInvariantLoad implementation.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83475 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 48 insertions, 7 deletions

diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index a3560a7..2dc99f5 100644
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -24,6 +24,7 @@
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetInstrDesc.h"
 #include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/DebugInfo.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/LeakDetector.h"
@@ -946,7 +947,7 @@ bool MachineInstr::isSafeToMove(const TargetInstrInfo *TII,
   // destination. The check for isInvariantLoad gives the targe the chance to
   // classify the load as always returning a constant, e.g. a constant pool
   // load.
-  if (TID->mayLoad() && !TII->isInvariantLoad(this))
+  if (TID->mayLoad() && !isInvariantLoad())
     // Otherwise, this is a real load.  If there is a store between the load and
     // end of block, or if the load is volatile, we can't move it.
     return !SawStore && !hasVolatileMemoryRef();
@@ -1005,6 +1006,46 @@ bool MachineInstr::hasVolatileMemoryRef() const {
   return false;
 }
 
+/// isInvariantLoad - Return true if this instruction is loading from a
+/// location whose value is invariant across the function.  For example,
+/// loading a value from the constant pool or from from the argument area
+/// of a function if it does not change.  This should only return true of
+/// *all* loads the instruction does are invariant (if it does multiple loads).
+bool MachineInstr::isInvariantLoad(AliasAnalysis *AA) const {
+  // If the instruction doesn't load at all, it isn't an invariant load.
+  if (!TID->mayLoad())
+    return false;
+
+  // If the instruction has lost its memoperands, conservatively assume that
+  // it may not be an invariant load.
+  if (memoperands_empty())
+    return false;
+
+  const MachineFrameInfo *MFI = getParent()->getParent()->getFrameInfo();
+
+  for (mmo_iterator I = memoperands_begin(),
+       E = memoperands_end(); I != E; ++I) {
+    if ((*I)->isVolatile()) return false;
+    if ((*I)->isStore()) return false;
+
+    if (const Value *V = (*I)->getValue()) {
+      // A load from a constant PseudoSourceValue is invariant.
+      if (const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(V))
+        if (PSV->isConstant(MFI))
+          continue;
+      // If we have an AliasAnalysis, ask it whether the memory is constant.
+      if (AA && AA->pointsToConstantMemory(V))
+        continue;
+    }
+
+    // Otherwise assume conservatively.
+    return false;
+  }
+
+  // Everything checks out.
+  return true;
+}
+
 void MachineInstr::dump() const {
   errs() << "  " << *this;
 }
diff --git a/lib/CodeGen/MachineLICM.cpp b/lib/CodeGen/MachineLICM.cpp
index 61678f1..b5827aa 100644
--- a/lib/CodeGen/MachineLICM.cpp
+++ b/lib/CodeGen/MachineLICM.cpp
@@ -28,6 +28,7 @@
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetMachine.h"
+#include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Support/Compiler.h"
@@ -47,6 +48,7 @@ namespace {
     BitVector AllocatableSet;
 
     // Various analyses that we use...
+    AliasAnalysis        *AA;      // Alias analysis info.
     MachineLoopInfo      *LI;      // Current MachineLoopInfo
     MachineDominatorTree *DT;      // Machine dominator tree for the cur loop
     MachineRegisterInfo  *RegInfo; // Machine register information
@@ -72,6 +74,7 @@ namespace {
       AU.setPreservesCFG();
       AU.addRequired<MachineLoopInfo>();
       AU.addRequired<MachineDominatorTree>();
+      AU.addRequired<AliasAnalysis>();
       AU.addPreserved<MachineLoopInfo>();
       AU.addPreserved<MachineDominatorTree>();
       MachineFunctionPass::getAnalysisUsage(AU);
@@ -144,6 +147,7 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
   // Get our Loop information...
   LI = &getAnalysis<MachineLoopInfo>();
   DT = &getAnalysis<MachineDominatorTree>();
+  AA = &getAnalysis<AliasAnalysis>();
 
   for (MachineLoopInfo::iterator
          I = LI->begin(), E = LI->end(); I != E; ++I) {
@@ -214,7 +218,7 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
     // Okay, this instruction does a load. As a refinement, we allow the target
     // to decide whether the loaded value is actually a constant. If so, we can
     // actually use it as a load.
-    if (!TII->isInvariantLoad(&I))
+    if (!I.isInvariantLoad(AA))
       // FIXME: we should be able to sink loads with no other side effects if
       // there is nothing that can change memory from here until the end of
       // block. This is a trivial form of alias analysis.
@@ -259,8 +263,6 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
 
     // Don't hoist an instruction that uses or defines a physical register.
     if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
-      // If this is a physical register use, we can't move it.  If it is a def,
-      // we can move it, but only if the def is dead.
       if (MO.isUse()) {
         // If the physreg has no defs anywhere, it's just an ambient register
         // and we can freely move its uses. Alternatively, if it's allocatable,
diff --git a/lib/CodeGen/MachineSink.cpp b/lib/CodeGen/MachineSink.cpp
index 636dad8..e5c3420 100644
--- a/lib/CodeGen/MachineSink.cpp
+++ b/lib/CodeGen/MachineSink.cpp
@@ -178,8 +178,6 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
     if (Reg == 0) continue;
     
     if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
-      // If this is a physical register use, we can't move it.  If it is a def,
-      // we can move it, but only if the def is dead.
       if (MO.isUse()) {
         // If the physreg has no defs anywhere, it's just an ambient register
         // and we can freely move its uses. Alternatively, if it's allocatable,
diff --git a/lib/CodeGen/ScheduleDAGInstrs.cpp b/lib/CodeGen/ScheduleDAGInstrs.cpp
index b55e606..f50844f 100644
--- a/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -375,7 +375,7 @@ void ScheduleDAGInstrs::BuildSchedGraph() {
         // Treat all other stores conservatively.
         goto new_chain;
     } else if (TID.mayLoad()) {
-      if (TII->isInvariantLoad(MI)) {
+      if (MI->isInvariantLoad()) {
         // Invariant load, no chain dependencies needed!
       } else if (const Value *V = getUnderlyingObjectForInstr(MI)) {
         // A load from a specific PseudoSourceValue. Add precise dependencies.