[AMDGPU] Tweak getTypeLegalizationCost()

Even though wide vectors are legal they still cost more as we
will have to eventually split them. Not all operations can
be uniformly done on vector types.

Conservatively add the cost of splitting at least to 8 dwords,
which is our widest possible load.

We are more or less lying to cost mode with this change but
this can prevent vectorizer from creation of wide vectors which
results in RA problems for us.

Differential Revision: https://reviews.llvm.org/D83078

diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index a3135a7..d902728 100644 (file)
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -11690,3 +11690,18 @@ bool SITargetLowering::requiresUniformRegister(MachineFunction &MF,
   SmallPtrSet<const Value *, 16> Visited;
   return hasCFUser(V, Visited, Subtarget->getWavefrontSize());
 }
+
+std::pair<int, MVT>
+SITargetLowering::getTypeLegalizationCost(const DataLayout &DL,
+                                          Type *Ty) const {
+  auto Cost = TargetLoweringBase::getTypeLegalizationCost(DL, Ty);
+  auto Size = DL.getTypeSizeInBits(Ty);
+  // Maximum load or store can handle 8 dwords for scalar and 4 for
+  // vector ALU. Let's assume anything above 8 dwords is expensive
+  // even if legal.
+  if (Size <= 256)
+    return Cost;
+
+  Cost.first = (Size + 255) / 256;
+  return Cost;
+}

diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.h b/llvm/lib/Target/AMDGPU/SIISelLowering.h
index ffe9140..f4c0764 100644 (file)
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.h
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.h
@@ -464,6 +464,9 @@ public:
                                       MachineFunction &MF,
                                       const SIRegisterInfo &TRI,
                                       SIMachineFunctionInfo &Info) const;
+
+  std::pair<int, MVT> getTypeLegalizationCost(const DataLayout &DL,
+                                              Type *Ty) const;
 };
 
 } // End namespace llvm

diff --git a/llvm/test/Analysis/CostModel/AMDGPU/add-sub.ll b/llvm/test/Analysis/CostModel/AMDGPU/add-sub.ll
index 9a2c010..609769f 100644 (file)
--- a/llvm/test/Analysis/CostModel/AMDGPU/add-sub.ll
+++ b/llvm/test/Analysis/CostModel/AMDGPU/add-sub.ll
@@ -90,7 +90,7 @@ define amdgpu_kernel void @add_v4i64(<4 x i64> addrspace(1)* %out, <4 x i64> add
 }
 
 ; ALL: 'add_v16i64'
-; ALL: estimated cost of 32 for {{.*}} add <16 x i64>
+; ALL: estimated cost of 128 for {{.*}} add <16 x i64>
 define amdgpu_kernel void @add_v16i64(<16 x i64> addrspace(1)* %out, <16 x i64> addrspace(1)* %vaddr, <16 x i64> %b) #0 {
   %vec = load <16 x i64>, <16 x i64> addrspace(1)* %vaddr
   %add = add <16 x i64> %vec, %b

diff --git a/llvm/test/Analysis/CostModel/AMDGPU/mul.ll b/llvm/test/Analysis/CostModel/AMDGPU/mul.ll
index 4d8a66e..fa36d39 100644 (file)
--- a/llvm/test/Analysis/CostModel/AMDGPU/mul.ll
+++ b/llvm/test/Analysis/CostModel/AMDGPU/mul.ll
@@ -90,7 +90,7 @@ define amdgpu_kernel void @mul_v4i64(<4 x i64> addrspace(1)* %out, <4 x i64> add
 
 
 ; ALL: 'mul_v8i64'
-; ALL: estimated cost of 128 for {{.*}} mul <8 x i64>
+; ALL: estimated cost of 256 for {{.*}} mul <8 x i64>
 define amdgpu_kernel void @mul_v8i64(<8 x i64> addrspace(1)* %out, <8 x i64> addrspace(1)* %vaddr, <8 x i64> %b) #0 {
   %vec = load <8 x i64>, <8 x i64> addrspace(1)* %vaddr
   %mul = mul <8 x i64> %vec, %b