Add skeletal code to increase the alignment of loads and stores when

we can infer it.  This will eventually help stuff, though it doesn't
do much right now because all fixed FI's have an alignment of 1.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46349 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 38 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index fc393e9ef2..57e7a04d2f 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -14,6 +14,8 @@
 
 #define DEBUG_TYPE "dagcombine"
 #include "llvm/CodeGen/SelectionDAG.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Target/TargetLowering.h"
@@ -4074,11 +4076,37 @@ bool DAGCombiner::CombineToPostIndexedLoadStore(SDNode *N) {
   return false;
 }
 
+/// InferAlignment - If we can infer some alignment information from this
+/// pointer, return it.
+static unsigned InferAlignment(SDOperand Ptr, SelectionDAG &DAG) {
+  // If this is a direct reference to a stack slot, use information about the
+  // stack slot's alignment.
+  if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Ptr)) {
+    return DAG.getMachineFunction().getFrameInfo()->
+         getObjectAlignment(FI->getIndex());
+  }
+  
+  // FIXME: Handle FI+CST.
+  
+  return 0;
+}
 
 SDOperand DAGCombiner::visitLOAD(SDNode *N) {
   LoadSDNode *LD  = cast<LoadSDNode>(N);
   SDOperand Chain = LD->getChain();
   SDOperand Ptr   = LD->getBasePtr();
+  
+  // Try to infer better alignment information than the load already has.
+  if (LD->isUnindexed()) {
+    if (unsigned Align = InferAlignment(Ptr, DAG)) {
+      if (Align > LD->getAlignment())
+        return DAG.getExtLoad(LD->getExtensionType(), LD->getValueType(0),
+                              Chain, Ptr, LD->getSrcValue(),
+                              LD->getSrcValueOffset(), LD->getLoadedVT(),
+                              LD->isVolatile(), Align);
+    }
+  }
+  
 
   // If load is not volatile and there are no uses of the loaded value (and
   // the updated indexed value in case of indexed loads), change uses of the
@@ -4189,6 +4217,16 @@ SDOperand DAGCombiner::visitSTORE(SDNode *N) {
   SDOperand Value = ST->getValue();
   SDOperand Ptr   = ST->getBasePtr();
   
+  // Try to infer better alignment information than the store already has.
+  if (ST->isUnindexed()) {
+    if (unsigned Align = InferAlignment(Ptr, DAG)) {
+      if (Align > ST->getAlignment())
+        return DAG.getTruncStore(Chain, Value, Ptr, ST->getSrcValue(),
+                                 ST->getSrcValueOffset(), ST->getStoredVT(),
+                                 ST->isVolatile(), Align);
+    }
+  }
+  
   // If this is a store of a bit convert, store the input value if the
   // resultant store does not need a higher alignment than the original.
   if (Value.getOpcode() == ISD::BIT_CONVERT && !ST->isTruncatingStore() &&