From 3e4fb70c6af53a2d00e057a7e4a8f93eb2ff2112 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Wed, 24 Sep 2008 00:06:15 +0000
Subject: [PATCH] Add a method to MachineInstr for testing whether it makes any
 volatile memory references.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56528 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/CodeGen/MachineInstr.h |  8 ++++++
 lib/CodeGen/MachineInstr.cpp        | 39 ++++++++++++++++++++++-------
 2 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/include/llvm/CodeGen/MachineInstr.h b/include/llvm/CodeGen/MachineInstr.h
index 3171af9606e..8efea624425 100644
--- a/include/llvm/CodeGen/MachineInstr.h
+++ b/include/llvm/CodeGen/MachineInstr.h
@@ -250,8 +250,16 @@ public:
   /// the instruction's location and its intended destination.
   bool isSafeToMove(const TargetInstrInfo *TII, bool &SawStore);
 
+  /// isSafeToReMat - Return true if it's safe to rematerialize the specified
+  /// instruction which defined the specified register instead of copying it.
   bool isSafeToReMat(const TargetInstrInfo *TII, unsigned DstReg);
 
+  /// hasVolatileMemoryRef - Return true if this instruction may have a
+  /// volatile memory reference, or if the information describing the
+  /// memory reference is not available. Return false if it is known to
+  /// have no volatile memory references.
+  bool hasVolatileMemoryRef() const;
+
   //
   // Debugging support
   //
diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index a365f20300f..7d44d4ee79f 100644
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -711,16 +711,11 @@ bool MachineInstr::isSafeToMove(const TargetInstrInfo *TII, bool &SawStore) {
   // 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() && !TII->isInvariantLoad(this))
     // Otherwise, this is a real load.  If there is a store between the load and
-    // end of block, we can't sink the load.
-    //
-    // FIXME: we can't do this transformation until we know that the load is
-    // not volatile, and machineinstrs don't keep this info. :(
-    //
-    //if (SawStore) 
-    return false;
-  }
+    // end of block, or if the laod is volatile, we can't move it.
+    return SawStore || hasVolatileMemoryRef();
+
   return true;
 }
 
@@ -749,6 +744,32 @@ bool MachineInstr::isSafeToReMat(const TargetInstrInfo *TII, unsigned DstReg) {
   return true;
 }
 
+/// hasVolatileMemoryRef - Return true if this instruction may have a
+/// volatile memory reference, or if the information describing the
+/// memory reference is not available. Return false if it is known to
+/// have no volatile memory references.
+bool MachineInstr::hasVolatileMemoryRef() const {
+  // An instruction known never to access memory won't have a volatile access.
+  if (!TID->mayStore() &&
+      !TID->mayLoad() &&
+      !TID->isCall() &&
+      !TID->hasUnmodeledSideEffects())
+    return false;
+
+  // Otherwise, if the instruction has no memory reference information,
+  // conservatively assume it wasn't preserved.
+  if (memoperands_empty())
+    return true;
+  
+  // Check the memory reference information for volatile references.
+  for (std::list<MachineMemOperand>::const_iterator I = memoperands_begin(),
+       E = memoperands_end(); I != E; ++I)
+    if (I->isVolatile())
+      return true;
+
+  return false;
+}
+
 void MachineInstr::dump() const {
   cerr << "  " << *this;
 }