Change SelectionDAG::getConstantPool to always set the alignment of the

ConstantPoolSDNode, using the target's preferred alignment for the
constant type.

In LegalizeDAG, when performing loads from the constant pool, the
ConstantPoolSDNode's alignment is used in the calls to getLoad and
getExtLoad.

This change prevents SelectionDAG::getLoad/getExtLoad from incorrectly
choosing the ABI alignment for constant pool loads when Alignment == 0.
The incorrect alignment is only a performance issue when ABI alignment
does not equal preferred alignment (i.e., on x86 it was generating
MOVUPS instead of MOVAPS for v4f32 constant loads when the default ABI
alignment for 128bit vectors is forced to 1 byte.)

Patch by Paul Redmond!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56253 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 793f5c9997..a6851ee804 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1019,6 +1019,9 @@ SDValue SelectionDAG::getJumpTable(int JTI, MVT VT, bool isTarget){
 SDValue SelectionDAG::getConstantPool(Constant *C, MVT VT,
                                       unsigned Alignment, int Offset,
                                       bool isTarget) {
+  if (Alignment == 0)
+    Alignment =
+      TLI.getTargetData()->getPreferredTypeAlignmentShift(C->getType());
   unsigned Opc = isTarget ? ISD::TargetConstantPool : ISD::ConstantPool;
   FoldingSetNodeID ID;
   AddNodeIDNode(ID, Opc, getVTList(VT), 0, 0);
@@ -1039,6 +1042,9 @@ SDValue SelectionDAG::getConstantPool(Constant *C, MVT VT,
 SDValue SelectionDAG::getConstantPool(MachineConstantPoolValue *C, MVT VT,
                                       unsigned Alignment, int Offset,
                                       bool isTarget) {
+  if (Alignment == 0)
+    Alignment =
+      TLI.getTargetData()->getPreferredTypeAlignmentShift(C->getType());
   unsigned Opc = isTarget ? ISD::TargetConstantPool : ISD::ConstantPool;
   FoldingSetNodeID ID;
   AddNodeIDNode(ID, Opc, getVTList(VT), 0, 0);