From a4b6404cf0ad8fae26188d780d583ef499f99b3b Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Mon, 28 Nov 2011 20:42:56 +0000
Subject: DAG combine should not increase alignment of loads / stores with
 alignment less than ABI alignment. These are loads / stores from / to
 "packed" data structures. Their alignments are intentionally under-specified.

rdar://10301431

llvm-svn: 145273
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 38 ++++++++++++++++++---------
 1 file changed, 26 insertions(+), 12 deletions(-)

(limited to 'llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp')

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index d8208a44338..2c4886a3c83 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6206,13 +6206,20 @@ SDValue DAGCombiner::visitLOAD(SDNode *N) {
 
   // Try to infer better alignment information than the load already has.
   if (OptLevel != CodeGenOpt::None && LD->isUnindexed()) {
-    if (unsigned Align = DAG.InferPtrAlignment(Ptr)) {
-      if (Align > LD->getAlignment())
-        return DAG.getExtLoad(LD->getExtensionType(), N->getDebugLoc(),
-                              LD->getValueType(0),
-                              Chain, Ptr, LD->getPointerInfo(),
-                              LD->getMemoryVT(),
-                              LD->isVolatile(), LD->isNonTemporal(), Align);
+    unsigned ABIAlign = TLI.getTargetData()->
+      getABITypeAlignment(LD->getMemoryVT().getTypeForEVT(*DAG.getContext()));
+    unsigned LDAlign = LD->getAlignment();
+    // Do not touch loads with explicit alignments that are smaller than ABI
+    // alignment to avoid breaking loads from "packed" types.
+    if (!LDAlign || LDAlign >= ABIAlign) {
+      if (unsigned Align = DAG.InferPtrAlignment(Ptr)) {
+        if (Align > LDAlign)
+          return DAG.getExtLoad(LD->getExtensionType(), N->getDebugLoc(),
+                                LD->getValueType(0),
+                                Chain, Ptr, LD->getPointerInfo(),
+                                LD->getMemoryVT(),
+                                LD->isVolatile(), LD->isNonTemporal(), Align);
+      }
     }
   }
 
@@ -6669,11 +6676,18 @@ SDValue DAGCombiner::visitSTORE(SDNode *N) {
 
   // Try to infer better alignment information than the store already has.
   if (OptLevel != CodeGenOpt::None && ST->isUnindexed()) {
-    if (unsigned Align = DAG.InferPtrAlignment(Ptr)) {
-      if (Align > ST->getAlignment())
-        return DAG.getTruncStore(Chain, N->getDebugLoc(), Value,
-                                 Ptr, ST->getPointerInfo(), ST->getMemoryVT(),
-                                 ST->isVolatile(), ST->isNonTemporal(), Align);
+    unsigned ABIAlign = TLI.getTargetData()->
+      getABITypeAlignment(ST->getMemoryVT().getTypeForEVT(*DAG.getContext()));
+    unsigned STAlign = ST->getAlignment();
+    // Do not touch stores with explicit alignments that are smaller than ABI
+    // alignment to avoid breaking stores from "packed" types.
+    if (!STAlign || STAlign >= ABIAlign) {
+      if (unsigned Align = DAG.InferPtrAlignment(Ptr)) {
+        if (Align > STAlign)
+          return DAG.getTruncStore(Chain, N->getDebugLoc(), Value,
+                                   Ptr, ST->getPointerInfo(), ST->getMemoryVT(),
+                                   ST->isVolatile(), ST->isNonTemporal(),Align);
+      }
     }
   }
 
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