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[RISCV][TTI] Extract subvector at index zero is free #81751

Merged
merged 2 commits into from
Feb 15, 2024
Merged

[RISCV][TTI] Extract subvector at index zero is free #81751

merged 2 commits into from
Feb 15, 2024

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preames
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@preames preames commented Feb 14, 2024 •
edited

Extracing a subvector at index zero corresponds to a type conversion and possibly a subregister operation. We will not emit a vslidedown. As such, they are free.

As an aside, it looks like we're not passing an index in for cases where the subvec type is scalable. For at least index zero, we probably should be.

@preames
[RISCV][TTI] Insert/Extract subvector at index zero are free
650e00d 
Inserting or extracing a subvector at index zero corresponds to a type
conversion and possibly a subregister operation.  We will not emit
a vslidedown or vslideup.  As such, they are free.

As an aside, it looks like we're not passing an index in for cases
where the subvec type is scalable.  For at least index zero, we
probably should be.
@llvmbot
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llvmbot commented Feb 14, 2024 •
edited

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-backend-risc-v

Author: Philip Reames (preames)

Changes

Inserting or extracing a subvector at index zero corresponds to a type conversion and possibly a subregister operation. We will not emit a vslidedown or vslideup. As such, they are free.

As an aside, it looks like we're not passing an index in for cases where the subvec type is scalable. For at least index zero, we probably should be.

Patch is 42.24 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/81751.diff

4 Files Affected:

  • (modified) llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp (+8)
  • (modified) llvm/test/Analysis/CostModel/RISCV/rvv-shuffle.ll (+4-4)
  • (modified) llvm/test/Analysis/CostModel/RISCV/shuffle-extract_subvector.ll (+36-36)
  • (modified) llvm/test/Transforms/SLPVectorizer/RISCV/remarks-insert-into-small-vector.ll (+1-1)
diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
index d1db47a6061e4e..247abfeb87ce9c 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
@@ -432,12 +432,20 @@ InstructionCost RISCVTTIImpl::getShuffleCost(TTI::ShuffleKind Kind,
     // must be implemented here.
     break;
   case TTI::SK_ExtractSubvector:
+    // Extract at zero is always a subregister extract
+    if (Index == 0)
+      return TTI::TCC_Free;
+
     // Example sequence:
     // vsetivli     zero, 4, e8, mf2, tu, ma (ignored)
     // vslidedown.vi  v8, v9, 2
     return LT.first *
            getRISCVInstructionCost(RISCV::VSLIDEDOWN_VI, LT.second, CostKind);
   case TTI::SK_InsertSubvector:
+    // Insert at zero is always a subregister insert
+    if (Index == 0)
+      return TTI::TCC_Free;
+
     // Example sequence:
     // vsetivli     zero, 4, e8, mf2, tu, ma (ignored)
     // vslideup.vi  v8, v9, 2
diff --git a/llvm/test/Analysis/CostModel/RISCV/rvv-shuffle.ll b/llvm/test/Analysis/CostModel/RISCV/rvv-shuffle.ll
index 4f3c7e2f90c655..b64dd5cfce8375 100644
--- a/llvm/test/Analysis/CostModel/RISCV/rvv-shuffle.ll
+++ b/llvm/test/Analysis/CostModel/RISCV/rvv-shuffle.ll
@@ -52,15 +52,15 @@ define void  @vector_broadcast() {
 
 define void @vector_insert_extract(<vscale x 4 x i32> %v0, <vscale x 16 x i32> %v1, <16 x i32> %v2) {
 ; CHECK-LABEL: 'vector_insert_extract'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %extract_fixed_from_scalable = call <16 x i32> @llvm.vector.extract.v16i32.nxv4i32(<vscale x 4 x i32> %v0, i64 0)
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %insert_fixed_into_scalable = call <vscale x 4 x i32> @llvm.vector.insert.nxv4i32.v16i32(<vscale x 4 x i32> %v0, <16 x i32> %v2, i64 0)
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %extract_fixed_from_scalable = call <16 x i32> @llvm.vector.extract.v16i32.nxv4i32(<vscale x 4 x i32> %v0, i64 0)
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %insert_fixed_into_scalable = call <vscale x 4 x i32> @llvm.vector.insert.nxv4i32.v16i32(<vscale x 4 x i32> %v0, <16 x i32> %v2, i64 0)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %extract_scalable_from_scalable = call <vscale x 4 x i32> @llvm.vector.extract.nxv4i32.nxv16i32(<vscale x 16 x i32> %v1, i64 0)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %insert_scalable_into_scalable = call <vscale x 16 x i32> @llvm.vector.insert.nxv16i32.nxv4i32(<vscale x 16 x i32> %v1, <vscale x 4 x i32> %v0, i64 0)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
 ; SIZE-LABEL: 'vector_insert_extract'
-; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %extract_fixed_from_scalable = call <16 x i32> @llvm.vector.extract.v16i32.nxv4i32(<vscale x 4 x i32> %v0, i64 0)
-; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %insert_fixed_into_scalable = call <vscale x 4 x i32> @llvm.vector.insert.nxv4i32.v16i32(<vscale x 4 x i32> %v0, <16 x i32> %v2, i64 0)
+; SIZE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %extract_fixed_from_scalable = call <16 x i32> @llvm.vector.extract.v16i32.nxv4i32(<vscale x 4 x i32> %v0, i64 0)
+; SIZE-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %insert_fixed_into_scalable = call <vscale x 4 x i32> @llvm.vector.insert.nxv4i32.v16i32(<vscale x 4 x i32> %v0, <16 x i32> %v2, i64 0)
 ; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %extract_scalable_from_scalable = call <vscale x 4 x i32> @llvm.vector.extract.nxv4i32.nxv16i32(<vscale x 16 x i32> %v1, i64 0)
 ; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %insert_scalable_into_scalable = call <vscale x 16 x i32> @llvm.vector.insert.nxv16i32.nxv4i32(<vscale x 16 x i32> %v1, <vscale x 4 x i32> %v0, i64 0)
 ; SIZE-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: ret void
diff --git a/llvm/test/Analysis/CostModel/RISCV/shuffle-extract_subvector.ll b/llvm/test/Analysis/CostModel/RISCV/shuffle-extract_subvector.ll
index 76cb1955a2b377..793786318a0a16 100644
--- a/llvm/test/Analysis/CostModel/RISCV/shuffle-extract_subvector.ll
+++ b/llvm/test/Analysis/CostModel/RISCV/shuffle-extract_subvector.ll
@@ -9,13 +9,13 @@
 
 define void @test_vXf64(<4 x double> %src256, <8 x double> %src512) {
 ; CHECK-LABEL: 'test_vXf64'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_01 = shufflevector <4 x double> %src256, <4 x double> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V256_01 = shufflevector <4 x double> %src256, <4 x double> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_23 = shufflevector <4 x double> %src256, <4 x double> undef, <2 x i32> <i32 2, i32 3>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_01 = shufflevector <8 x double> %src512, <8 x double> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V512_01 = shufflevector <8 x double> %src512, <8 x double> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_23 = shufflevector <8 x double> %src512, <8 x double> undef, <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_45 = shufflevector <8 x double> %src512, <8 x double> undef, <2 x i32> <i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_67 = shufflevector <8 x double> %src512, <8 x double> undef, <2 x i32> <i32 6, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_0123 = shufflevector <8 x double> %src512, <8 x double> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V512_0123 = shufflevector <8 x double> %src512, <8 x double> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_2345 = shufflevector <8 x double> %src512, <8 x double> undef, <4 x i32> <i32 2, i32 3, i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_4567 = shufflevector <8 x double> %src512, <8 x double> undef, <4 x i32> <i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of -1 for instruction: %V512_567u = shufflevector <8 x double> %src512, <8 x double> undef, <4 x i32> <i32 5, i32 6, i32 7, i32 poison>
@@ -36,13 +36,13 @@ define void @test_vXf64(<4 x double> %src256, <8 x double> %src512) {
 
 define void @test_vXi64(<4 x i64> %src256, <8 x i64> %src512) {
 ; CHECK-LABEL: 'test_vXi64'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_01 = shufflevector <4 x i64> %src256, <4 x i64> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V256_01 = shufflevector <4 x i64> %src256, <4 x i64> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_23 = shufflevector <4 x i64> %src256, <4 x i64> undef, <2 x i32> <i32 2, i32 3>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_01 = shufflevector <8 x i64> %src512, <8 x i64> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V512_01 = shufflevector <8 x i64> %src512, <8 x i64> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_23 = shufflevector <8 x i64> %src512, <8 x i64> undef, <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_45 = shufflevector <8 x i64> %src512, <8 x i64> undef, <2 x i32> <i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_67 = shufflevector <8 x i64> %src512, <8 x i64> undef, <2 x i32> <i32 6, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_0123 = shufflevector <8 x i64> %src512, <8 x i64> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V512_0123 = shufflevector <8 x i64> %src512, <8 x i64> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_2345 = shufflevector <8 x i64> %src512, <8 x i64> undef, <4 x i32> <i32 2, i32 3, i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_4567 = shufflevector <8 x i64> %src512, <8 x i64> undef, <4 x i32> <i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
@@ -61,15 +61,15 @@ define void @test_vXi64(<4 x i64> %src256, <8 x i64> %src512) {
 
 define void @test_vXi32(<4 x i32> %src128, <8 x i32> %src256, <16 x i32> %src512) {
 ; CHECK-LABEL: 'test_vXi32'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V128_01 = shufflevector <4 x i32> %src128, <4 x i32> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V128_01 = shufflevector <4 x i32> %src128, <4 x i32> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V128_23 = shufflevector <4 x i32> %src128, <4 x i32> undef, <2 x i32> <i32 2, i32 3>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_01 = shufflevector <8 x i32> %src256, <8 x i32> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V256_01 = shufflevector <8 x i32> %src256, <8 x i32> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_23 = shufflevector <8 x i32> %src256, <8 x i32> undef, <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_45 = shufflevector <8 x i32> %src256, <8 x i32> undef, <2 x i32> <i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_67 = shufflevector <8 x i32> %src256, <8 x i32> undef, <2 x i32> <i32 6, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_0123 = shufflevector <8 x i32> %src256, <8 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V256_0123 = shufflevector <8 x i32> %src256, <8 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_4567 = shufflevector <8 x i32> %src256, <8 x i32> undef, <4 x i32> <i32 4, i32 5, i32 6, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_01 = shufflevector <16 x i32> %src512, <16 x i32> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V512_01 = shufflevector <16 x i32> %src512, <16 x i32> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_23 = shufflevector <16 x i32> %src512, <16 x i32> undef, <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_45 = shufflevector <16 x i32> %src512, <16 x i32> undef, <2 x i32> <i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_67 = shufflevector <16 x i32> %src512, <16 x i32> undef, <2 x i32> <i32 6, i32 7>
@@ -77,11 +77,11 @@ define void @test_vXi32(<4 x i32> %src128, <8 x i32> %src256, <16 x i32> %src512
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_AB = shufflevector <16 x i32> %src512, <16 x i32> undef, <2 x i32> <i32 10, i32 11>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_CD = shufflevector <16 x i32> %src512, <16 x i32> undef, <2 x i32> <i32 12, i32 13>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_EF = shufflevector <16 x i32> %src512, <16 x i32> undef, <2 x i32> <i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_0123 = shufflevector <16 x i32> %src512, <16 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V512_0123 = shufflevector <16 x i32> %src512, <16 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_4567 = shufflevector <16 x i32> %src512, <16 x i32> undef, <4 x i32> <i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_89AB = shufflevector <16 x i32> %src512, <16 x i32> undef, <4 x i32> <i32 8, i32 9, i32 10, i32 11>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_CDEF = shufflevector <16 x i32> %src512, <16 x i32> undef, <4 x i32> <i32 12, i32 13, i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_01234567 = shufflevector <16 x i32> %src512, <16 x i32> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V512_01234567 = shufflevector <16 x i32> %src512, <16 x i32> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_89ABCDEF = shufflevector <16 x i32> %src512, <16 x i32> undef, <8 x i32> <i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
@@ -112,15 +112,15 @@ define void @test_vXi32(<4 x i32> %src128, <8 x i32> %src256, <16 x i32> %src512
 
 define void @test_vXi16(<4 x i16> %src64, <8 x i16> %src128, <16 x i16> %src256, <32 x i16> %src512) {
 ; CHECK-LABEL: 'test_vXi16'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V64_01 = shufflevector <4 x i16> %src64, <4 x i16> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V64_01 = shufflevector <4 x i16> %src64, <4 x i16> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V64_23 = shufflevector <4 x i16> %src64, <4 x i16> undef, <2 x i32> <i32 2, i32 3>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V128_01 = shufflevector <8 x i16> %src128, <8 x i16> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V128_01 = shufflevector <8 x i16> %src128, <8 x i16> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V128_23 = shufflevector <8 x i16> %src128, <8 x i16> undef, <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V128_45 = shufflevector <8 x i16> %src128, <8 x i16> undef, <2 x i32> <i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V128_67 = shufflevector <8 x i16> %src128, <8 x i16> undef, <2 x i32> <i32 6, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V128_0123 = shufflevector <8 x i16> %src128, <8 x i16> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V128_0123 = shufflevector <8 x i16> %src128, <8 x i16> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V128_4567 = shufflevector <8 x i16> %src128, <8 x i16> undef, <4 x i32> <i32 4, i32 5, i32 6, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_01 = shufflevector <16 x i16> %src256, <16 x i16> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V256_01 = shufflevector <16 x i16> %src256, <16 x i16> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_23 = shufflevector <16 x i16> %src256, <16 x i16> undef, <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_45 = shufflevector <16 x i16> %src256, <16 x i16> undef, <2 x i32> <i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_67 = shufflevector <16 x i16> %src256, <16 x i16> undef, <2 x i32> <i32 6, i32 7>
@@ -128,15 +128,15 @@ define void @test_vXi16(<4 x i16> %src64, <8 x i16> %src128, <16 x i16> %src256,
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_AB = shufflevector <16 x i16> %src256, <16 x i16> undef, <2 x i32> <i32 10, i32 11>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_CD = shufflevector <16 x i16> %src256, <16 x i16> undef, <2 x i32> <i32 12, i32 13>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_EF = shufflevector <16 x i16> %src256, <16 x i16> undef, <2 x i32> <i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_0123 = shufflevector <16 x i16> %src256, <16 x i16> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V256_0123 = shufflevector <16 x i16> %src256, <16 x i16> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_2345 = shufflevector <16 x i16> %src256, <16 x i16> undef, <4 x i32> <i32 2, i32 3, i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_4567 = shufflevector <16 x i16> %src256, <16 x i16> undef, <4 x i32> <i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_6789 = shufflevector <16 x i16> %src256, <16 x i16> undef, <4 x i32> <i32 6, i32 7, i32 8, i32 9>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_89AB = shufflevector <16 x i16> %src256, <16 x i16> undef, <4 x i32> <i32 8, i32 9, i32 10, i32 11>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_CDEF = shufflevector <16 x i16> %src256, <16 x i16> undef, <4 x i32> <i32 12, i32 13, i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_01234567 = shufflevector <16 x i16> %src256, <16 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V256_01234567 = shufflevector <16 x i16> %src256, <16 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V256_89ABCDEF = shufflevector <16 x i16> %src256, <16 x i16> undef, <8 x i32> <i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_00_01 = shufflevector <32 x i16> %src512, <32 x i16> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %V512_00_01 = shufflevector <32 x i16> %src512, <32 x i16> undef, <2 x i32> <i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_02_03 = shufflevector <32 x i16> %src512, <32 x i16> undef, <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_04_05 = shufflevector <32 x i16> %src512, <32 x i16> undef, <2 x i32> <i32 4, i32 5>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_06_07 = shufflevector <32 x i16> %src512, <32 x i16> undef, <2 x i32> <i32 6, i32 7>
@@ -152,7 +152,7 @@ define void @test_vXi16(<4 x i16> %src64, <8 x i16> %src128, <16 x i16> %src256,
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %V512_1A_1B = shufflevector <32 x...
[truncated]

@preames preames mentioned this pull request Feb 14, 2024
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lukel97
lukel97 reviewed Feb 14, 2024
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llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp Outdated
// Example sequence:
// vsetivli zero, 4, e8, mf2, tu, ma (ignored)
// vslidedown.vi v8, v9, 2
return LT.first *
getRISCVInstructionCost(RISCV::VSLIDEDOWN_VI, LT.second, CostKind);
case TTI::SK_InsertSubvector:
// Insert at zero is always a subregister insert
if (Index == 0)
return TTI::TCC_Free;
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For inserts we still may need a vslideup if the subvec to insert is < LMUL 1 and the vector isn't undef

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Good catch. It doesn't necessarily need to be a slideup, but we do need an instruction to perform the merge, you're right.

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I reframed this review to be specifically about the extract case. Once this lands, I'll take another attempt at the insert case. That ones slightly annoying since I don't see an easy way in the current API to figure out what the passthru is. I may have to resort to inspecting the operands of the instruction directly.

@preames
Backout insert change.
93e6a78 
As pointed in review, that's a bit more complicated.
@preames preames changed the title [RISCV][TTI] Insert/Extract subvector at index zero are free [RISCV][TTI] Extract subvector at index zero is free Feb 14, 2024
lukel97
lukel97 approved these changes Feb 15, 2024
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LGTM.

Not related to this patch, how come we end up handling scalable vectors in the shuffle cost anyway? The only valid shufflevector for a scalable vector is a zeroinitializer mask IIUC, i.e. SK_Broadcast

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lukel97 commented Feb 15, 2024

LGTM.

Not related to this patch, how come we end up handling scalable vectors in the shuffle cost anyway? The only valid shufflevector for a scalable vector is a zeroinitializer mask IIUC, i.e. SK_Broadcast

Looks like we reuse getShuffleCost for the vector.insert/vector.extract intrinsics:

llvm-project/llvm/include/llvm/CodeGen/BasicTTIImpl.h

Lines 1636 to 1655 in 8ce1448

case Intrinsic::vector_extract: {
// FIXME: Handle case where a scalable vector is extracted from a scalable
// vector
if (isa<ScalableVectorType>(RetTy))
return BaseT::getIntrinsicInstrCost(ICA, CostKind);
unsigned Index = cast<ConstantInt>(Args[1])->getZExtValue();
return thisT()->getShuffleCost(
TTI::SK_ExtractSubvector, cast<VectorType>(Args[0]->getType()),
std::nullopt, CostKind, Index, cast<VectorType>(RetTy));
}
case Intrinsic::vector_insert: {
// FIXME: Handle case where a scalable vector is inserted into a scalable
// vector
if (isa<ScalableVectorType>(Args[1]->getType()))
return BaseT::getIntrinsicInstrCost(ICA, CostKind);
unsigned Index = cast<ConstantInt>(Args[2])->getZExtValue();
return thisT()->getShuffleCost(
TTI::SK_InsertSubvector, cast<VectorType>(Args[0]->getType()),
std::nullopt, CostKind, Index, cast<VectorType>(Args[1]->getType()));
}

lukel97 added a commit to lukel97/llvm-project that referenced this pull request Feb 15, 2024
@lukel97
[RISCV] Cost @llvm.vector.{extract,insert} as free at index 0
49ee117 
This builds upon llvm#81751 by handling the @llvm.vector.{extract,insert}
intrinsics.

I believe we'll need the logic in both places as fixed vector extracts/inserts
of fixed vectors will use the shuffle cost hook, whereas anything with a
scalable return type will use the intrinsic cost hook.
@lukel97 lukel97 mentioned this pull request Feb 15, 2024
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@preames preames merged commit 3a62693 into llvm:main Feb 15, 2024
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topperc commented Feb 15, 2024

@reames I think this commit is causing a failure on test/Analysis/CostModel/RISCV/rvv-vectorextract.ll ? I guess @lukel97 added that test after you made this PR?

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topperc added a commit that referenced this pull request Feb 15, 2024
@topperc
Revert "[RISCV][TTI] Extract subvector at index zero is free (#81751)"
834d11c 
This reverts commit 3a62693.

Causes tests added by fc0b67e to fail.
preames added a commit that referenced this pull request Feb 16, 2024
@preames
Reapply "[RISCV][TTI] Extract subvector at index zero is free (#81751)"
2549c24 
This reverts commit 834d11c which was
a revert of my 3a62693.  I had failed
to rebase after new tests added overnight by
fc0b67e.

Original commit message follows:

Extracing a subvector at index zero corresponds to a type conversion and
possibly a subregister operation. We will not emit a vslidedown. As such,
they are free.

As an aside, it looks like we're not passing an index in for cases where
the subvec type is scalable. For at least index zero, we probably should be.

Revert "Revert "[RISCV][TTI] Extract subvector at index zero is free (#81751)""
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lukel97 commented Feb 16, 2024

@reames I think this commit is causing a failure on test/Analysis/CostModel/RISCV/rvv-vectorextract.ll ? I guess @lukel97 added that test after you made this PR?

My bad, I forgot that this PR would need rebased after adding them

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preames commented Feb 16, 2024

@reames I think this commit is causing a failure on test/Analysis/CostModel/RISCV/rvv-vectorextract.ll ? I guess @lukel97 added that test after you made this PR?

My bad, I forgot that this PR would need rebased after adding them

You did nothing wrong here. This was entirely my error.

@preames preames deleted the pr-riscv-tti-insert-extract-subvector-at-zero branch February 16, 2024 02:12
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