commit 1c487869f5d47a7ad89d21ed9912bf89f25e3b72
author Evan Cheng <evan.cheng@apple.com> Mon Nov 28 20:42:56 2011 +0000
committer Evan Cheng <evan.cheng@apple.com> Mon Nov 28 20:42:56 2011 +0000
tree cde919c751e7eb9430c088f0cb0d02f7047a395c
parent 678cda052cab001bb47f95eaee60b0e3e458b753

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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145273 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index d8208a4..2c4886a 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6206,13 +6206,20 @@
 
   // 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 @@
 
   // 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);
+      }
     }
   }