[CostModel][X86] Improve cost estimation of insert_subvector shuffle patterns of legalized types

In cases where the base/sub vector type in an insert_subvector pattern legalize to the same width through splitting, we can assume that the shuffle becomes free as the legalized vectors will not overlap.

Note this isn't true if the vectors have been widened during legalization (e.g. v2f32 insertion into v4f32 would legalize to v4f32 into v4f32).

Noticed while working on adding processShuffleMasks handling for SK_PermuteTwoSrc.

Author: RKSimon

llvm/lib/Target/X86/X86TargetTransformInfo.cpp

@@ -1630,14 +1630,19 @@ InstructionCost X86TTIImpl::getShuffleCost(
 
   // Subvector insertions are cheap if the subvectors are aligned.
   // Note that in general, the insertion starting at the beginning of a vector
-  // isn't free, because we need to preserve the rest of the wide vector.
+  // isn't free, because we need to preserve the rest of the wide vector,
+  // but if the destination vector legalizes to the same width as the subvector
+  // then the insertion will simplify to a (free) register copy.
   if (Kind == TTI::SK_InsertSubvector && LT.second.isVector()) {
     int NumElts = LT.second.getVectorNumElements();
     std::pair<InstructionCost, MVT> SubLT = getTypeLegalizationCost(SubTp);
     if (SubLT.second.isVector()) {
       int NumSubElts = SubLT.second.getVectorNumElements();
+      bool MatchingTypes =
+          NumElts == NumSubElts &&
+          (SubTp->getElementCount().getKnownMinValue() % NumSubElts) == 0;
       if ((Index % NumSubElts) == 0 && (NumElts % NumSubElts) == 0)
-        return SubLT.first;
+        return MatchingTypes ? TTI::TCC_Free : SubLT.first;
     }
 
     // If the insertion isn't aligned, treat it like a 2-op shuffle.

llvm/test/Analysis/CostModel/X86/shuffle-concat_subvector-codesize.ll

@@ -64,11 +64,18 @@ define <16 x i32> @concat_sext_v8i16_v16i32(<8 x i16> %a0, <8 x i16> %a1) {
 }
 
 define <8 x i32> @concat_sext_v4i1_v8i32(<4 x i1> %a0, <4 x i1> %a1) {
-; CHECK-LABEL: define <8 x i32> @concat_sext_v4i1_v8i32(
-; CHECK-SAME: <4 x i1> [[A0:%.*]], <4 x i1> [[A1:%.*]]) #[[ATTR0]] {
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i1> [[A0]], <4 x i1> [[A1]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
-; CHECK-NEXT:    [[R:%.*]] = sext <8 x i1> [[TMP1]] to <8 x i32>
-; CHECK-NEXT:    ret <8 x i32> [[R]]
+; SSE-LABEL: define <8 x i32> @concat_sext_v4i1_v8i32(
+; SSE-SAME: <4 x i1> [[A0:%.*]], <4 x i1> [[A1:%.*]]) #[[ATTR0]] {
+; SSE-NEXT:    [[X0:%.*]] = sext <4 x i1> [[A0]] to <4 x i32>
+; SSE-NEXT:    [[X1:%.*]] = sext <4 x i1> [[A1]] to <4 x i32>
+; SSE-NEXT:    [[R:%.*]] = shufflevector <4 x i32> [[X0]], <4 x i32> [[X1]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; SSE-NEXT:    ret <8 x i32> [[R]]
+;
+; AVX-LABEL: define <8 x i32> @concat_sext_v4i1_v8i32(
+; AVX-SAME: <4 x i1> [[A0:%.*]], <4 x i1> [[A1:%.*]]) #[[ATTR0]] {
+; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i1> [[A0]], <4 x i1> [[A1]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; AVX-NEXT:    [[R:%.*]] = sext <8 x i1> [[TMP1]] to <8 x i32>
+; AVX-NEXT:    ret <8 x i32> [[R]]
 ;
   %x0 = sext <4 x i1> %a0 to <4 x i32>
   %x1 = sext <4 x i1> %a1 to <4 x i32>
@@ -90,11 +97,18 @@ define <8 x i16> @concat_trunc_v4i32_v8i16(<4 x i32> %a0, <4 x i32> %a1) {
 }
 
 define <8 x ptr> @concat_inttoptr_v4i32_v8iptr(<4 x i32> %a0, <4 x i32> %a1) {
-; CHECK-LABEL: define <8 x ptr> @concat_inttoptr_v4i32_v8iptr(
-; CHECK-SAME: <4 x i32> [[A0:%.*]], <4 x i32> [[A1:%.*]]) #[[ATTR0]] {
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i32> [[A0]], <4 x i32> [[A1]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
-; CHECK-NEXT:    [[R:%.*]] = inttoptr <8 x i32> [[TMP1]] to <8 x ptr>
-; CHECK-NEXT:    ret <8 x ptr> [[R]]
+; SSE-LABEL: define <8 x ptr> @concat_inttoptr_v4i32_v8iptr(
+; SSE-SAME: <4 x i32> [[A0:%.*]], <4 x i32> [[A1:%.*]]) #[[ATTR0]] {
+; SSE-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i32> [[A0]], <4 x i32> [[A1]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; SSE-NEXT:    [[R:%.*]] = inttoptr <8 x i32> [[TMP1]] to <8 x ptr>
+; SSE-NEXT:    ret <8 x ptr> [[R]]
+;
+; AVX-LABEL: define <8 x ptr> @concat_inttoptr_v4i32_v8iptr(
+; AVX-SAME: <4 x i32> [[A0:%.*]], <4 x i32> [[A1:%.*]]) #[[ATTR0]] {
+; AVX-NEXT:    [[X0:%.*]] = inttoptr <4 x i32> [[A0]] to <4 x ptr>
+; AVX-NEXT:    [[X1:%.*]] = inttoptr <4 x i32> [[A1]] to <4 x ptr>
+; AVX-NEXT:    [[R:%.*]] = shufflevector <4 x ptr> [[X0]], <4 x ptr> [[X1]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; AVX-NEXT:    ret <8 x ptr> [[R]]
 ;
   %x0 = inttoptr <4 x i32> %a0 to <4 x ptr>
   %x1 = inttoptr <4 x i32> %a1 to <4 x ptr>
@@ -138,9 +152,8 @@ define <8 x double> @concat_fpext_v4f32_v8f64(<4 x float> %a0, <4 x float> %a1)
 define <16 x float> @concat_fptrunc_v8f64_v16f32(<8 x double> %a0, <8 x double> %a1) {
 ; CHECK-LABEL: define <16 x float> @concat_fptrunc_v8f64_v16f32(
 ; CHECK-SAME: <8 x double> [[A0:%.*]], <8 x double> [[A1:%.*]]) #[[ATTR0]] {
-; CHECK-NEXT:    [[X0:%.*]] = fptrunc <8 x double> [[A0]] to <8 x float>
-; CHECK-NEXT:    [[X1:%.*]] = fptrunc <8 x double> [[A1]] to <8 x float>
-; CHECK-NEXT:    [[R:%.*]] = shufflevector <8 x float> [[X0]], <8 x float> [[X1]], <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <8 x double> [[A0]], <8 x double> [[A1]], <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
+; CHECK-NEXT:    [[R:%.*]] = fptrunc <16 x double> [[TMP1]] to <16 x float>
 ; CHECK-NEXT:    ret <16 x float> [[R]]
 ;
   %x0 = fptrunc <8 x double> %a0 to <8 x float>