[PATCH] D33457: [LV] Update type in cost model for scalarization

[Matthew Simpson via Phabricator via llvm-commits]

mssimpso created this revision.
Herald added subscribers: javed.absar, mzolotukhin.

For non-uniform instructions marked for scalarization, we should update `VectorTy` when computing instruction costs to reflect the scalar type. In addition to determining instruction costs, this type is also used to signal that all instructions in the loop will be scalarized. This currently affects memory instructions and non-pointer induction variables and their updates. (We also mark GEPs scalar after vectorization, but their cost is computed together with memory instructions.) For scalarized induction updates, this patch also scales the scalar cost by the vectorization factor, corresponding to each induction step.


https://reviews.llvm.org/D33457

Files:
  lib/Transforms/Vectorize/LoopVectorize.cpp
  test/Transforms/LoopVectorize/AArch64/no_vector_instructions.ll


Index: test/Transforms/LoopVectorize/AArch64/no_vector_instructions.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopVectorize/AArch64/no_vector_instructions.ll
@@ -0,0 +1,25 @@
+; RUN: opt < %s -loop-vectorize -force-vector-interleave=1 -S --debug-only=loop-vectorize 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64--linux-gnu"
+
+; CHECK-LABEL: all_scalar
+; CHECK:       LV: Found scalar instruction: %i.next = add nuw nsw i64 %i, 2
+; CHECK:       LV: Found an estimated cost of 2 for VF 2 For instruction: %i.next = add nuw nsw i64 %i, 2
+; CHECK:       LV: Not considering vector loop of width 2 because it will not generate any vector instructions
+;
+define void @all_scalar(i64* %a, i64 %n) {
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i64 [ 0, %entry ], [ %i.next, %for.body ]
+  %tmp0 = getelementptr i64, i64* %a, i64 %i
+  store i64 0, i64* %tmp0, align 1
+  %i.next = add nuw nsw i64 %i, 2
+  %cond = icmp eq i64 %i.next, %n
+  br i1 %cond, label %for.end, label %for.body
+
+for.end:
+  ret void
+}
Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -7154,8 +7154,9 @@
   Type *VectorTy;
   unsigned C = getInstructionCost(I, VF, VectorTy);
 
-  bool TypeNotScalarized =
-      VF > 1 && !VectorTy->isVoidTy() && TTI.getNumberOfParts(VectorTy) < VF;
+  bool TypeNotScalarized = VF > 1 && !VectorTy->isVoidTy() &&
+                           TTI.getNumberOfParts(VectorTy) < VF &&
+                           VectorTy->isVectorTy();
   return VectorizationCostTy(C, TypeNotScalarized);
 }
 
@@ -7238,7 +7239,7 @@
   Type *RetTy = I->getType();
   if (canTruncateToMinimalBitwidth(I, VF))
     RetTy = IntegerType::get(RetTy->getContext(), MinBWs[I]);
-  VectorTy = ToVectorTy(RetTy, VF);
+  VectorTy = isScalarAfterVectorization(I, VF) ? RetTy : ToVectorTy(RetTy, VF);
   auto SE = PSE.getSE();
 
   // TODO: We need to estimate the cost of intrinsic calls.
@@ -7371,9 +7372,10 @@
     } else if (Legal->isUniform(Op2)) {
       Op2VK = TargetTransformInfo::OK_UniformValue;
     }
-    SmallVector<const Value *, 4> Operands(I->operand_values()); 
-    return TTI.getArithmeticInstrCost(I->getOpcode(), VectorTy, Op1VK,
-                                      Op2VK, Op1VP, Op2VP, Operands);
+    SmallVector<const Value *, 4> Operands(I->operand_values());
+    unsigned N = isScalarAfterVectorization(I, VF) ? VF : 1;
+    return N * TTI.getArithmeticInstrCost(I->getOpcode(), VectorTy, Op1VK,
+                                          Op2VK, Op1VP, Op2VP, Operands);
   }
   case Instruction::Select: {
     SelectInst *SI = cast<SelectInst>(I);
@@ -7396,7 +7398,15 @@
   }
   case Instruction::Store:
   case Instruction::Load: {
-    VectorTy = ToVectorTy(getMemInstValueType(I), VF);
+    unsigned Width = VF;
+    if (Width > 1) {
+      InstWidening Decision = getWideningDecision(I, Width);
+      assert(Decision != CM_Unknown &&
+             "CM decision should be taken at this point");
+      if (Decision == CM_Scalarize)
+        Width = 1;
+    }
+    VectorTy = ToVectorTy(getMemInstValueType(I), Width);
     return getMemoryInstructionCost(I, VF);
   }
   case Instruction::ZExt:


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