[llvm] 124fa5c - [AArch64] - Improve costing for Identity shuffles for SVE targets. (#165375)
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Tue Nov 18 11:52:47 PST 2025
Author: Pawan Nirpal
Date: 2025-11-18T11:52:43-08:00
New Revision: 124fa5ce5f211dff6dbdc5f433a445386ac2c26b
URL: https://github.com/llvm/llvm-project/commit/124fa5ce5f211dff6dbdc5f433a445386ac2c26b
DIFF: https://github.com/llvm/llvm-project/commit/124fa5ce5f211dff6dbdc5f433a445386ac2c26b.diff
LOG: [AArch64] - Improve costing for Identity shuffles for SVE targets. (#165375)
Identity masks can be treated as free when scalable vectorization is
possible making the check agnostic of the vectorization policy
fixed/scalable, This allows for aggressive vector combines for identity
shuffle masks.
Added:
llvm/test/Transforms/VectorCombine/AArch64/identity-shuffle-sve.ll
Modified:
llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
llvm/test/Analysis/CostModel/AArch64/shuffle-other.ll
Removed:
################################################################################
diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index 7dd571c7fe60d..bf195ca210e9b 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -6000,6 +6000,15 @@ AArch64TTIImpl::getShuffleCost(TTI::ShuffleKind Kind, VectorType *DstTy,
SrcTy = DstTy;
}
+ // Check for identity masks, which we can treat as free for both fixed and
+ // scalable vector paths.
+ if (!Mask.empty() && LT.second.isFixedLengthVector() &&
+ (Kind == TTI::SK_PermuteTwoSrc || Kind == TTI::SK_PermuteSingleSrc) &&
+ all_of(enumerate(Mask), [](const auto &M) {
+ return M.value() < 0 || M.value() == (int)M.index();
+ }))
+ return 0;
+
// Segmented shuffle matching.
if (Kind == TTI::SK_PermuteSingleSrc && isa<FixedVectorType>(SrcTy) &&
!Mask.empty() && SrcTy->getPrimitiveSizeInBits().isNonZero() &&
@@ -6047,14 +6056,6 @@ AArch64TTIImpl::getShuffleCost(TTI::ShuffleKind Kind, VectorType *DstTy,
all_of(Mask, [](int E) { return E < 8; }))
return getPerfectShuffleCost(Mask);
- // Check for identity masks, which we can treat as free.
- if (!Mask.empty() && LT.second.isFixedLengthVector() &&
- (Kind == TTI::SK_PermuteTwoSrc || Kind == TTI::SK_PermuteSingleSrc) &&
- all_of(enumerate(Mask), [](const auto &M) {
- return M.value() < 0 || M.value() == (int)M.index();
- }))
- return 0;
-
// Check for other shuffles that are not SK_ kinds but we have native
// instructions for, for example ZIP and UZP.
unsigned Unused;
diff --git a/llvm/test/Analysis/CostModel/AArch64/shuffle-other.ll b/llvm/test/Analysis/CostModel/AArch64/shuffle-other.ll
index 4579acb9b3555..255877fcdca5e 100644
--- a/llvm/test/Analysis/CostModel/AArch64/shuffle-other.ll
+++ b/llvm/test/Analysis/CostModel/AArch64/shuffle-other.ll
@@ -490,3 +490,15 @@ define void @vst4(ptr %p) {
ret void
}
+
+define void @identity_shuffle_costs() #0 {
+bb:
+ ; CHECK-LABEL: 'identity_shuffle_costs'
+ ; CHECK: Cost Model: Found costs of 0 for: %shufflevector142 = shufflevector <16 x i8> zeroinitializer, <16 x i8> zeroinitializer, <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: Cost Model: Found costs of 0 for: %shufflevector84 = shufflevector <16 x i8> zeroinitializer, <16 x i8> poison, <32 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, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+ %shufflevector142 = shufflevector <16 x i8> zeroinitializer, <16 x i8> zeroinitializer, <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>
+ %shufflevector84 = shufflevector <16 x i8> zeroinitializer, <16 x i8> poison, <32 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, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+ ret void
+}
+
+attributes #0 = { "target-features"="+sve,+neon" }
diff --git a/llvm/test/Transforms/VectorCombine/AArch64/identity-shuffle-sve.ll b/llvm/test/Transforms/VectorCombine/AArch64/identity-shuffle-sve.ll
new file mode 100644
index 0000000000000..f499ea9a20c6f
--- /dev/null
+++ b/llvm/test/Transforms/VectorCombine/AArch64/identity-shuffle-sve.ll
@@ -0,0 +1,61 @@
+; NOTE: This test is expected to test the Identity shuffle costs as zero, regardless of scalable or fixed width shuffle vectors, As a result enabling aggressive vector-combine transforms.
+; RUN: opt -passes=vector-combine -S %s | FileCheck %s
+target triple = "aarch64-unknown-linux-gnu"
+
+define i32 @ham(ptr %call12) #0 {
+; CHECK-LABEL: define i32 @ham(
+; CHECK-SAME: ptr [[CALL12:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK: [[TMP2:%.*]] = mul nuw nsw <32 x i32> [[TMP1:%.*]], <i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 19595, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767, i32 32767>
+
+; CHECK: [[TMP5:%.*]] = mul nuw <32 x i32> [[TMP4:%.*]], <i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 38470, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097, i32 16762097>
+
+; CHECK: [[TMP8:%.*]] = mul nuw <32 x i32> [[TMP7:%.*]], <i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 7471, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568, i32 16759568>
+
+bb:
+ br label %bb48
+
+bb48: ; preds = %bb48, %bb
+ %phi49 = phi i64 [ 0, %bb ], [ %add86, %bb48 ]
+ %mul50 = mul i64 %phi49, 3
+ %getelementptr53 = getelementptr i8, ptr %call12, i64 %mul50
+ %load54 = load <48 x i8>, ptr %getelementptr53, align 1
+ %shufflevector = shufflevector <48 x i8> %load54, <48 x i8> poison, <16 x i32> <i32 0, i32 3, i32 6, i32 9, i32 12, i32 15, i32 18, i32 21, i32 24, i32 27, i32 30, i32 33, i32 36, i32 39, i32 42, i32 45>
+ %zext57 = zext <16 x i8> %shufflevector to <16 x i32>
+ %mul58 = mul nuw nsw <16 x i32> %zext57, splat (i32 19595)
+ %zext59 = zext <16 x i8> %shufflevector to <16 x i32>
+ %mul60 = mul nuw nsw <16 x i32> %zext59, splat (i32 38470)
+ %zext61 = zext <16 x i8> %shufflevector to <16 x i32>
+ %mul62 = mul nuw nsw <16 x i32> %zext61, splat (i32 7471)
+ %add63 = add nuw nsw <16 x i32> %mul58, splat (i32 32768)
+ %add64 = add nuw nsw <16 x i32> %add63, %mul60
+ %add65 = add nuw nsw <16 x i32> %add64, %mul62
+ %lshr = lshr <16 x i32> %add65, splat (i32 16)
+ %trunc66 = trunc nuw <16 x i32> %lshr to <16 x i8>
+ %mul67 = mul nuw nsw <16 x i32> %zext57, splat (i32 32767)
+ %mul68 = mul nuw <16 x i32> %zext59, splat (i32 16762097)
+ %mul69 = mul nuw <16 x i32> %zext61, splat (i32 16759568)
+ %add70 = add nuw nsw <16 x i32> %mul67, splat (i32 32768)
+ %add71 = add nuw <16 x i32> %add70, %mul68
+ %add72 = add <16 x i32> %add71, %mul69
+ %lshr73 = lshr <16 x i32> %add72, splat (i32 16)
+ %trunc74 = trunc <16 x i32> %lshr73 to <16 x i8>
+ %mul75 = mul nuw nsw <16 x i32> %zext57, splat (i32 13282)
+ %mul76 = mul nuw <16 x i32> %zext59, splat (i32 16744449)
+ %mul77 = mul nuw nsw <16 x i32> %zext61, splat (i32 19485)
+ %add78 = add nuw nsw <16 x i32> %mul75, splat (i32 32768)
+ %add79 = add nuw <16 x i32> %add78, %mul76
+ %add80 = add nuw <16 x i32> %add79, %mul77
+ %lshr81 = lshr <16 x i32> %add80, splat (i32 16)
+ %trunc82 = trunc <16 x i32> %lshr81 to <16 x i8>
+ %shufflevector83 = shufflevector <16 x i8> %trunc66, <16 x i8> %trunc74, <32 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, i32 16, i32 17, i32 18, i32 19, i32 20, i32 21, i32 22, i32 23, i32 24, i32 25, i32 26, i32 27, i32 28, i32 29, i32 30, i32 31>
+ %shufflevector84 = shufflevector <16 x i8> %trunc82, <16 x i8> poison, <32 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, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+ store <32 x i8> %shufflevector83, ptr %getelementptr53, align 1
+ %add86 = add nuw i64 %phi49, 16
+ %icmp87 = icmp eq i64 %add86, %mul50
+ br i1 %icmp87, label %bb205, label %bb48
+
+bb205: ; preds = %bb48, %bb
+ ret i32 0
+}
+
+attributes #0 = { vscale_range(1,16) "target-features"="+sve,+neon"}
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