Revert r145273 and fix in SelectionDAG::InferPtrAlignment() instead.

Conservatively returns zero when the GV does not specify an alignment nor is it
initialized. Previously it returns ABI alignment for type of the GV. However, if
the type is a "packed" type, then the under-specified alignments is attached to
the load / store instructions. In that case, the alignment of the type cannot be
trusted.
rdar://10464621

llvm-svn: 145300

2 files changed, 17 insertions, 27 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2c4886a3c83..d8208a44338 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6206,20 +6206,13 @@ SDValue DAGCombiner::visitLOAD(SDNode *N) {
 
   // Try to infer better alignment information than the load already has.
   if (OptLevel != CodeGenOpt::None && LD->isUnindexed()) {
-    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);
-      }
+    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);
     }
   }
 
@@ -6676,18 +6669,11 @@ SDValue DAGCombiner::visitSTORE(SDNode *N) {
 
   // Try to infer better alignment information than the store already has.
   if (OptLevel != CodeGenOpt::None && ST->isUnindexed()) {
-    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);
-      }
+    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);
     }
   }
 
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index a772a46ba60..024a1637371 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6564,7 +6564,11 @@ unsigned SelectionDAG::InferPtrAlignment(SDValue Ptr) const {
         }
       }
       if (!Align)
-        Align = TLI.getTargetData()->getABITypeAlignment(GV->getType());
+        // Conservatively returns zero here instead of using ABI alignment for
+        // type of the GV. If the type is a "packed" type, then the under-
+        // specified alignments is attached to the load / store instructions.
+        // In that case, the alignment of the type cannot be trusted.
+        return 0;
     }
     return MinAlign(Align, GVOffset);
   }