LoadStoreVectorizer: Split even sized illegal chains properly

Implement isLegalToVectorizeLoadChain for AMDGPU to avoid
producing private address spaces accesses that will need to be
split up later. This was doing the wrong thing in the case
where the queried chain was an even number of elements.

A possible <4 x i32> store was being split into
store <2 x i32>
store i32
store i32

rather than
store <2 x i32>
store <2 x i32>

when legal.

llvm-svn: 295933

3 files changed, 42 insertions, 3 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
index 6d2e2f0bbbb..a780a76c86a 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
@@ -129,6 +129,31 @@ unsigned AMDGPUTTIImpl::getLoadStoreVecRegBitWidth(unsigned AddrSpace) const {
   }
 }
 
+bool AMDGPUTTIImpl::isLegalToVectorizeMemChain(unsigned ChainSizeInBytes,
+                                               unsigned Alignment,
+                                               unsigned AddrSpace) const {
+  // We allow vectorization of flat stores, even though we may need to decompose
+  // them later if they may access private memory. We don't have enough context
+  // here, and legalization can handle it.
+  if (AddrSpace == AMDGPUAS::PRIVATE_ADDRESS) {
+    return (Alignment >= 4 || ST->hasUnalignedScratchAccess()) &&
+      ChainSizeInBytes <= ST->getMaxPrivateElementSize();
+  }
+  return true;
+}
+
+bool AMDGPUTTIImpl::isLegalToVectorizeLoadChain(unsigned ChainSizeInBytes,
+                                                unsigned Alignment,
+                                                unsigned AddrSpace) const {
+  return isLegalToVectorizeMemChain(ChainSizeInBytes, Alignment, AddrSpace);
+}
+
+bool AMDGPUTTIImpl::isLegalToVectorizeStoreChain(unsigned ChainSizeInBytes,
+                                                 unsigned Alignment,
+                                                 unsigned AddrSpace) const {
+  return isLegalToVectorizeMemChain(ChainSizeInBytes, Alignment, AddrSpace);
+}
+
 unsigned AMDGPUTTIImpl::getMaxInterleaveFactor(unsigned VF) {
   // Semi-arbitrary large amount.
   return 64;
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h
index 3f72a63679f..c64c4bf5f6a 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h
@@ -78,6 +78,17 @@ public:
   unsigned getNumberOfRegisters(bool Vector);
   unsigned getRegisterBitWidth(bool Vector);
   unsigned getLoadStoreVecRegBitWidth(unsigned AddrSpace) const;
+
+  bool isLegalToVectorizeMemChain(unsigned ChainSizeInBytes,
+                                  unsigned Alignment,
+                                  unsigned AddrSpace) const;
+  bool isLegalToVectorizeLoadChain(unsigned ChainSizeInBytes,
+                                   unsigned Alignment,
+                                   unsigned AddrSpace) const;
+  bool isLegalToVectorizeStoreChain(unsigned ChainSizeInBytes,
+                                    unsigned Alignment,
+                                    unsigned AddrSpace) const;
+
   unsigned getMaxInterleaveFactor(unsigned VF);
 
   int getArithmeticInstrCost(
diff --git a/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp b/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
index 20fbcf4533d..4409d7a404f 100644
--- a/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
@@ -432,9 +432,12 @@ Vectorizer::splitOddVectorElts(ArrayRef<Instruction *> Chain,
   unsigned ElementSizeBytes = ElementSizeBits / 8;
   unsigned SizeBytes = ElementSizeBytes * Chain.size();
   unsigned NumLeft = (SizeBytes - (SizeBytes % 4)) / ElementSizeBytes;
-  if (NumLeft == Chain.size())
-    --NumLeft;
-  else if (NumLeft == 0)
+  if (NumLeft == Chain.size()) {
+    if ((NumLeft & 1) == 0)
+      NumLeft /= 2; // Split even in half
+    else
+      --NumLeft;    // Split off last element
+  } else if (NumLeft == 0)
     NumLeft = 1;
   return std::make_pair(Chain.slice(0, NumLeft), Chain.slice(NumLeft));
 }