From 2d7a830ff3010f15680da05f62daf4eeedfe1e23 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 25 Jan 2008 07:20:16 +0000
Subject: [PATCH] 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.

llvm-svn: 46349
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index fc393e9ef237..57e7a04d2ff1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/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() &&