Fix canFoldInAddressingMode in DAGCombiner.cpp

[fdeferriere]

Summary

In the function canFoldInAddressingMode, VT is computed as the type of the destination/source of a LOAD/STORE operations, instead of the memory type of the operation.
On targets with a scaling factor on the offset of the LOAD/STORE operations, the function may return false for actually valid cases. This may then prevent the selection of profitable pre or post indexed load/store operations, and instead select pre or post indexed load/store for unprofitable cases.

[qcolombet]

Hi François,

Any chance you can add a test case for this change?
I reckon that may be difficult, but if you can come up with something that would be great!

Thanks,
-Quentin

[fdeferriere]

Hi Quentin,

I compiled a number of benches with an LLVM/arm compiler, and looked for differences in code generation with/without this patch, with no success. I also failed to reproduce it on a dedicated test case.I did not try on other targets
Thus, sorry, I won't be able to provide you with a test case for this patch.

-François.

[qcolombet]

Thanks for trying François.

LGTM then.

I'll commit on your behalf, shortly.

Cheers,
-Quentin

llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

 /// and that N may be folded in the load / store addressing mode.
 static bool canFoldInAddressingMode(SDNode *N, SDNode *Use,
                                     SelectionDAG &DAG,
                                     const TargetLowering &TLI) {
   EVT VT;
   if (LoadSDNode *LD  = dyn_cast<LoadSDNode>(Use)) {
     if (LD->isIndexed() || LD->getBasePtr().getNode() != N)
       return false;
-    VT = Use->getValueType(0);
+    VT = LD->getMemoryVT();
   } else if (StoreSDNode *ST  = dyn_cast<StoreSDNode>(Use)) {
     if (ST->isIndexed() || ST->getBasePtr().getNode() != N)
       return false;
-    VT = ST->getValue().getValueType();
+    VT = ST->getMemoryVT();
   } else
     return false;
 
   TargetLowering::AddrMode AM;
   if (N->getOpcode() == ISD::ADD) {
     ConstantSDNode *Offset = dyn_cast<ConstantSDNode>(N->getOperand(1));
     if (Offset)
       // [reg +/- imm]