[TTI][X86] getShuffleCosts - for SK_PermuteTwoSrc, if the masks are known to be "inlane" no need to scale the costs by worst-case legalization

SK_PermuteTwoSrc legalization has to assume any of the legalised source registers could be referenced in split shuffles, but if we already know that each 128-bit lane only references elements from the same lane of the source operands, then this scaling won't occur.

Hopefully this can help with llvm#113356 without us having to get full processShuffleMasks canonicalization finished first.

Author: RKSimon

llvm/lib/Target/X86/X86TargetTransformInfo.cpp

@@ -1775,7 +1775,7 @@ InstructionCost X86TTIImpl::getShuffleCost(
   }
 
   // For 2-input shuffles, we must account for splitting the 2 inputs into many.
-  if (Kind == TTI::SK_PermuteTwoSrc && LT.first != 1) {
+  if (Kind == TTI::SK_PermuteTwoSrc && !IsInLaneShuffle && LT.first != 1) {
     // We assume that source and destination have the same vector type.
     InstructionCost NumOfDests = LT.first;
     InstructionCost NumOfShufflesPerDest = LT.first * 2 - 1;

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

@@ -9,18 +9,11 @@
 ; RUN: opt -mtriple=x86_64-- -mcpu=x86-64-v3 -passes="default<O3>" -S < %s  | FileCheck %s --check-prefixes=AVX,AVX2
 
 define <4 x double> @PR94546(<4 x double> %a, <4 x double> %b) {
-; SSE2-LABEL: @PR94546(
-; SSE2-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[A:%.*]], <4 x double> [[B:%.*]], <2 x i32> <i32 0, i32 6>
-; SSE2-NEXT:    [[TMP2:%.*]] = shufflevector <4 x double> [[A]], <4 x double> [[B]], <2 x i32> <i32 1, i32 7>
-; SSE2-NEXT:    [[TMP3:%.*]] = fadd <2 x double> [[TMP1]], [[TMP2]]
-; SSE2-NEXT:    [[TMP4:%.*]] = shufflevector <2 x double> [[TMP3]], <2 x double> poison, <4 x i32> <i32 0, i32 poison, i32 poison, i32 1>
-; SSE2-NEXT:    ret <4 x double> [[TMP4]]
-;
-; SSE4-LABEL: @PR94546(
-; SSE4-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[A:%.*]], <4 x double> [[B:%.*]], <4 x i32> <i32 0, i32 poison, i32 poison, i32 6>
-; SSE4-NEXT:    [[TMP2:%.*]] = shufflevector <4 x double> [[A]], <4 x double> [[B]], <4 x i32> <i32 1, i32 poison, i32 poison, i32 7>
-; SSE4-NEXT:    [[TMP3:%.*]] = fadd <4 x double> [[TMP1]], [[TMP2]]
-; SSE4-NEXT:    ret <4 x double> [[TMP3]]
+; SSE-LABEL: @PR94546(
+; SSE-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[A:%.*]], <4 x double> [[B:%.*]], <4 x i32> <i32 0, i32 poison, i32 poison, i32 6>
+; SSE-NEXT:    [[TMP2:%.*]] = shufflevector <4 x double> [[A]], <4 x double> [[B]], <4 x i32> <i32 1, i32 poison, i32 poison, i32 7>
+; SSE-NEXT:    [[TMP3:%.*]] = fadd <4 x double> [[TMP1]], [[TMP2]]
+; SSE-NEXT:    ret <4 x double> [[TMP3]]
 ;
 ; AVX-LABEL: @PR94546(
 ; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[A:%.*]], <4 x double> [[B:%.*]], <4 x i32> <i32 0, i32 poison, i32 poison, i32 6>
@@ -50,4 +43,5 @@ define <4 x double> @PR94546(<4 x double> %a, <4 x double> %b) {
 ;; NOTE: These prefixes are unused and the list is autogenerated. Do not add tests below this line:
 ; AVX1: {{.*}}
 ; AVX2: {{.*}}
-; SSE: {{.*}}
+; SSE2: {{.*}}
+; SSE4: {{.*}}