[PATCH] D123638: [SLP][AArch64] Implement lookahead operand reordering score of splat loads for AArch64

[Vasileios Porpodas via Phabricator via llvm-commits]

vporpo created this revision.
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The original patch (https://reviews.llvm.org/D121354) targets x86 and adjusts
the lookahead score of splat loads ad they can be done by the `movddup`
instruction that combines the load and the broadcast and is cheap to execute.

A similar issue shows up on AArch64. The `ld1r` instruction performs a broadcast
load and is cheap to execute.

This patch implements the TargetTransformInfo hooks for AArch64.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D123638

Files:
  llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
  llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
  llvm/test/Transforms/SLPVectorizer/AArch64/splat-loads.ll


Index: llvm/test/Transforms/SLPVectorizer/AArch64/splat-loads.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/AArch64/splat-loads.ll
+++ llvm/test/Transforms/SLPVectorizer/AArch64/splat-loads.ll
@@ -10,21 +10,21 @@
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[GEP_1_0:%.*]] = getelementptr inbounds double, double* [[ARRAY1:%.*]], i64 0
 ; CHECK-NEXT:    [[GEP_2_0:%.*]] = getelementptr inbounds double, double* [[ARRAY2:%.*]], i64 0
+; CHECK-NEXT:    [[GEP_2_1:%.*]] = getelementptr inbounds double, double* [[ARRAY2]], i64 1
+; CHECK-NEXT:    [[LD_2_0:%.*]] = load double, double* [[GEP_2_0]], align 8
+; CHECK-NEXT:    [[LD_2_1:%.*]] = load double, double* [[GEP_2_1]], align 8
 ; CHECK-NEXT:    [[TMP0:%.*]] = bitcast double* [[GEP_1_0]] to <2 x double>*
 ; CHECK-NEXT:    [[TMP1:%.*]] = load <2 x double>, <2 x double>* [[TMP0]], align 8
-; CHECK-NEXT:    [[TMP2:%.*]] = bitcast double* [[GEP_2_0]] to <2 x double>*
-; CHECK-NEXT:    [[TMP3:%.*]] = load <2 x double>, <2 x double>* [[TMP2]], align 8
-; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[TMP3]], <2 x double> poison, <2 x i32> <i32 1, i32 0>
-; CHECK-NEXT:    [[TMP4:%.*]] = fmul <2 x double> [[TMP1]], [[SHUFFLE]]
-; CHECK-NEXT:    [[TMP5:%.*]] = extractelement <2 x double> [[SHUFFLE]], i32 1
-; CHECK-NEXT:    [[TMP6:%.*]] = insertelement <2 x double> poison, double [[TMP5]], i32 0
-; CHECK-NEXT:    [[TMP7:%.*]] = extractelement <2 x double> [[SHUFFLE]], i32 0
-; CHECK-NEXT:    [[TMP8:%.*]] = insertelement <2 x double> [[TMP6]], double [[TMP7]], i32 1
-; CHECK-NEXT:    [[TMP9:%.*]] = fmul <2 x double> [[TMP1]], [[TMP8]]
-; CHECK-NEXT:    [[TMP10:%.*]] = fadd <2 x double> [[TMP4]], [[TMP9]]
-; CHECK-NEXT:    [[TMP11:%.*]] = extractelement <2 x double> [[TMP10]], i32 0
-; CHECK-NEXT:    [[TMP12:%.*]] = extractelement <2 x double> [[TMP10]], i32 1
-; CHECK-NEXT:    [[ADD3:%.*]] = fadd double [[TMP11]], [[TMP12]]
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <2 x double> poison, double [[LD_2_0]], i32 0
+; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <2 x double> [[TMP2]], double [[LD_2_0]], i32 1
+; CHECK-NEXT:    [[TMP4:%.*]] = fmul <2 x double> [[TMP1]], [[TMP3]]
+; CHECK-NEXT:    [[TMP5:%.*]] = insertelement <2 x double> poison, double [[LD_2_1]], i32 0
+; CHECK-NEXT:    [[TMP6:%.*]] = insertelement <2 x double> [[TMP5]], double [[LD_2_1]], i32 1
+; CHECK-NEXT:    [[TMP7:%.*]] = fmul <2 x double> [[TMP1]], [[TMP6]]
+; CHECK-NEXT:    [[TMP8:%.*]] = fadd <2 x double> [[TMP4]], [[TMP7]]
+; CHECK-NEXT:    [[TMP9:%.*]] = extractelement <2 x double> [[TMP8]], i32 0
+; CHECK-NEXT:    [[TMP10:%.*]] = extractelement <2 x double> [[TMP8]], i32 1
+; CHECK-NEXT:    [[ADD3:%.*]] = fadd double [[TMP9]], [[TMP10]]
 ; CHECK-NEXT:    ret double [[ADD3]]
 ;
 entry:
Index: llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
===================================================================
--- llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
+++ llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
@@ -280,6 +280,11 @@
     return isLegalMaskedGatherScatter(DataType);
   }
 
+  bool isLegalBroadcastLoad(Type *ElementTy, unsigned NumElements) const {
+    // ld1r
+    return ST->hasNEON();
+  }
+
   bool isLegalNTStore(Type *DataType, Align Alignment) {
     // NOTE: The logic below is mostly geared towards LV, which calls it with
     //       vectors with 2 elements. We might want to improve that, if other
Index: llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -2697,6 +2697,20 @@
       { TTI::SK_Reverse, MVT::nxv4i1,   1 },
       { TTI::SK_Reverse, MVT::nxv2i1,   1 },
     };
+
+    // Check for broadcast loads.
+    if (Kind == TTI::SK_Broadcast) {
+      bool IsLoad = !Args.empty() && llvm::all_of(Args, [](const Value *V) {
+        return isa<LoadInst>(V);
+      });
+      if (IsLoad) {
+        assert(isLegalBroadcastLoad(Tp->getElementType(),
+                                    LT.second.getVectorNumElements()) &&
+               "Expected this to be accepted by isLegalBroadcastLoad()");
+        return 0; // broadcast is handled by ld1r
+      }
+    }
+
     if (const auto *Entry = CostTableLookup(ShuffleTbl, Kind, LT.second))
       return LT.first * Entry->Cost;
   }


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