From be8137b0b461d5a4bc8c94441d7360e23cc526a7 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Wed, 7 Oct 2009 17:38:06 +0000
Subject: 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.

llvm-svn: 83475
---
 llvm/lib/CodeGen/MachineInstr.cpp | 43 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

(limited to 'llvm/lib/CodeGen/MachineInstr.cpp')

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index a3560a77b65..2dc99f5bb71 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/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;
 }
-- 
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