commit 810cb6296264b49b99aa24161f8fd6fdd2aa03d4
author Matt Arsenault <Matthew.Arsenault@amd.com> Fri Dec 12 00:00:24 2014 +0000
committer Matt Arsenault <Matthew.Arsenault@amd.com> Fri Dec 12 00:00:24 2014 +0000
tree 14bf3f44205fb5fda4d9a68a2e5357a8bba7aa80
parent 482f9be1758def59e03c2168aa43a1fb0a1a3f0c

Add target hook for whether it is profitable to reduce load widths

Add an option to disable optimization to shrink truncated larger type
loads to smaller type loads. On SI this prevents using scalar load
instructions in some cases, since there are no scalar extloads.

llvm-svn: 224084

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 38a0661..ed3d06c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6036,6 +6036,9 @@
       LN0->getMemoryVT().getSizeInBits() < ExtVT.getSizeInBits() + ShAmt)
     return SDValue();
 
+  if (!TLI.shouldReduceLoadWidth(LN0, ExtType, ExtVT))
+    return SDValue();
+
   EVT PtrType = N0.getOperand(1).getValueType();
 
   if (PtrType == MVT::Untyped || PtrType.isExtended())

llvm/lib/Target/R600/AMDGPUISelLowering.cpp

diff --git a/llvm/lib/Target/R600/AMDGPUISelLowering.cpp b/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
index 3537179..0e34b46 100644
--- a/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/R600/AMDGPUISelLowering.cpp
@@ -432,6 +432,29 @@
   return (ScalarVT != MVT::f32 && ScalarVT != MVT::f64);
 }
 
+bool AMDGPUTargetLowering::shouldReduceLoadWidth(SDNode *N,
+                                                 ISD::LoadExtType,
+                                                 EVT NewVT) const {
+
+  unsigned NewSize = NewVT.getStoreSizeInBits();
+
+  // If we are reducing to a 32-bit load, this is always better.
+  if (NewSize == 32)
+    return true;
+
+  EVT OldVT = N->getValueType(0);
+  unsigned OldSize = OldVT.getStoreSizeInBits();
+
+  // Don't produce extloads from sub 32-bit types. SI doesn't have scalar
+  // extloads, so doing one requires using a buffer_load. In cases where we
+  // still couldn't use a scalar load, using the wider load shouldn't really
+  // hurt anything.
+
+  // If the old size already had to be an extload, there's no harm in continuing
+  // to reduce the width.
+  return (OldSize < 32);
+}
+
 bool AMDGPUTargetLowering::isLoadBitCastBeneficial(EVT LoadTy,
                                                    EVT CastTy) const {
   if (LoadTy.getSizeInBits() != CastTy.getSizeInBits())

llvm/lib/Target/R600/AMDGPUISelLowering.h

diff --git a/llvm/lib/Target/R600/AMDGPUISelLowering.h b/llvm/lib/Target/R600/AMDGPUISelLowering.h
index 36b4ee6..7386eae 100644
--- a/llvm/lib/Target/R600/AMDGPUISelLowering.h
+++ b/llvm/lib/Target/R600/AMDGPUISelLowering.h
@@ -124,6 +124,9 @@
 
   bool isFPImmLegal(const APFloat &Imm, EVT VT) const override;
   bool ShouldShrinkFPConstant(EVT VT) const override;
+  bool shouldReduceLoadWidth(SDNode *Load,
+                             ISD::LoadExtType ExtType,
+                             EVT ExtVT) const override;
 
   bool isLoadBitCastBeneficial(EVT, EVT) const override;
   SDValue LowerReturn(SDValue Chain, CallingConv::ID CallConv,