thesyncim · Oct 31, 2026 · Oct 31, 2026 · Oct 31, 2026 · Oct 31, 2026 · Oct 31, 2026
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
@@ -61,8 +61,13 @@ jobs:
       - name: Test tsvc (amd64, SIMD)
         run: make tsvc-test
 
-      - name: Install qemu-user-static
-        run: sudo apt-get update && sudo apt-get install -y qemu-user-static
+      # ubuntu-26.04 has no qemu-user-static: qemu-user ships the static
+      # emulators there, without the -static names the Makefile runs.
+      - name: Install qemu-user
+        run: |
+          sudo apt-get update && sudo apt-get install -y qemu-user
+          command -v qemu-aarch64-static || sudo ln -s "$(command -v qemu-aarch64)" /usr/local/bin/qemu-aarch64-static
+          qemu-aarch64-static --version
 
       - name: Test tsvc (arm64, qemu)
         run: make tsvc-test-qemu-arm64

diff --git a/AGENTS.md b/AGENTS.md
@@ -94,18 +94,21 @@ safety argument stays structural:
   the loop runs at least once (`x` may be a nil pointer the scalar loop never reads), and
   the overlap check and the vector loop use the locals; the fallback is the original loop.
   Arrays, pointers to slices, maps, and the result of a call stay rejected.
-- A store is `ident[i]` where `i` is *exactly* the loop variable (`index`). A load
-  may also be `ident[i+e]`, `ident[e+i]` or `ident[i-e]` for a loop-invariant integer
-  `e` (`indexAt`, `Load.Off`). A slice that is also stored may be read only at a
-  constant positive offset in a forward loop: iteration i then reads what a later
-  iteration writes, so the scalar loop sees the old value and the emitter loads it
-  before any store of the chunk (`statements` hoists those loads). A negative
-  offset is a recurrence (`ReasonCarriedDependence`); a variable distance or a
-  loop that counts down is `ReasonOffsetOfStored`. The length check is
-  against the last index read (`lastIndex`), and offset loads are not capped at the
-  limit. Every other store and load is `ident[i]` (`index`) — `dst[i+1]`, `dst[2*i]` are rejected outright, regardless of
-  whether they're actually dependent. That is what guarantees no two
-  iterations touch the same element.
+- A store or a load is `ident[i]`, `ident[i+e]`, `ident[e+i]` or `ident[i-e]` where
+  `i` is *exactly* the loop variable and `e` a loop-invariant integer (`indexAt`,
+  `Store.Off`, `Load.Off`). Every store to one slice is at the same offset
+  (`ReasonStoreOffsets` otherwise), so each iteration writes its own element. A slice
+  that is also stored may be read at that offset, or at a constant positive distance
+  past it in a forward loop: iteration i then reads what a later iteration writes, so
+  the scalar loop sees the old value and the emitter loads it before any store of the
+  chunk (`statements` hoists those loads). A negative distance is a recurrence
+  (`ReasonCarriedDependence`); a variable distance or a loop that counts down is
+  `ReasonOffsetOfStored`. The length check is against the last index touched
+  (`lastIndex`); offset loads are not capped at the limit, and a store at an offset
+  is capped at the limit plus the offset (`destination`), so it writes nothing the
+  scalar loop does not. `dst[2*i]` and `dst[i][j]` are rejected outright, regardless
+  of whether they're actually dependent. That is what guarantees no two iterations
+  touch the same element.
 - A non-slice operand becomes an `Invariant` only if it is a variable, a
   constant, a conversion or negation of one, or a sum, difference, product or
   bitwise combination of two (`invariant`). It is evaluated

diff --git a/BUGS.md b/BUGS.md
@@ -2,11 +2,11 @@
 
 loopvec rewrites code to use `GOEXPERIMENT=simd`, which is new, so most of what it hits
 is in the Go toolchain. This file lists the Go issues that affect loopvec. "tip" means
-gotip, "1.27.1" is the release toolchain loopvec is tested against.
+gotip, "1.27.3" is the release toolchain loopvec is tested against.
 
 | Issue | Status | Affects | loopvec's answer |
 |---|---|---|---|
-| [#80657](https://github.com/golang/go/issues/80657) simd in a method: internal compiler error | fixed on tip (CL 839405), still crashes on 1.27.1 | `-methods` | methods are skipped unless `-methods` is passed |
+| [#80657](https://github.com/golang/go/issues/80657) simd in a method: internal compiler error | fixed on tip (CL 839405), still crashes on 1.27.3 | `-methods` | methods are skipped unless `-methods` is passed |
 | [#80835](https://github.com/golang/go/issues/80835) legacy SSE encodings in functions using simd cause AVX-SSE transition penalties | open, fix pending (CLs 825145, 825146, in tip) | speed of any scalar float code that runs after a rewritten loop, in the same function or another | none; the portable `simd` package has no `ClearAVXUpperBits` |
 | [#81844](https://github.com/golang/go/issues/81844) blank identifier parameters rejected | fixed on tip (CL 841145) | every rewrite of a function with a `_` parameter | the generated file renames them `_p0`, `_p1`, ... |
 | [#81845](https://github.com/golang/go/issues/81845) calls left unresolved when inlined into a package initializer | closed as a duplicate of [#80689](https://github.com/golang/go/issues/80689), which is open | loops in package-level `var x = func() {...}()` | not rewritten (the generated initializer fails to link), see `package_initializer_no_rewrite.txt` and `toolexec_package_initializer.txt` |
@@ -19,7 +19,7 @@ gotip, "1.27.1" is the release toolchain loopvec is tested against.
 
 A function with a receiver that contains simd code failed to compile with
 `internal compiler error: missing Types entry`. loopvec does not rewrite loops in methods
-by default; `-methods` turns it on. The fix is on tip. On 1.27.1 the crash is still there,
+by default; `-methods` turns it on. The fix is on tip. On 1.27.3 the crash is still there,
 and `flag_methods_ice.txt` pins it, so that test starts failing when the pinned toolchain
 gets the fix. Reported by someone else; the fix is [CL 839405](https://go.dev/cl/839405).
 

diff --git a/Makefile b/Makefile
@@ -1,4 +1,4 @@
-export GOTOOLCHAIN ?= go1.27.1
+export GOTOOLCHAIN ?= go1.27.3
 
 .DEFAULT_GOAL := build
 

diff --git a/README.md b/README.md
@@ -45,6 +45,7 @@ operations that lower to **AVX-512/AVX2/NEON** depending on the target CPU:
 | `for i := range x { if x[i] < 0 { x[i] = 0 } }`, `if c { dst[i] = u } else if d { dst[i] = v } else { dst[i] = w }` | compare, then select (`IfElse`): ReLU, leaky ReLU, ReLU6, hard tanh, clamp, sign, step; also when the branches assign a temporary (`t := x[i]+3; if t < 0 { t = 0 } else if t > 6 { t = 6 }`: hard sigmoid, hard swish, cubic SiLU) |
 | `for i := range v.Values { v.Values[i] *= a }`, `dst.f[i] += src.f[i]` | a slice reached through a field (`x.f`, `x.f.g`); the root must not be assigned in the loop, and the field is copied into a local once |
 | `for i := range dst { dst[i] = a[i+1] - a[i] }`, `work[j] += a[row*lda+j]` | read at an offset from the index (stencil, row of a 2-D slice); a slice the loop also writes is read only at a constant positive offset (`a[i] = a[i+1] + b[i]`) |
+| `b[i*ldb+j] = a[i*lda+j]`, `c[row+j] += alpha * x[j]`, `line[off+x] = v` | store at an offset from the index (row of a 2-D slice); every store to a slice is at the same offset, and the slice is read only there or at a constant positive distance past it |
 
 Supported element types: `int8`, `int16`, `int32`, `int64`, `uint8`, `uint16`,
 `uint32`, `uint64`, `float32`, `float64`.

diff --git a/bench/bench_test.go b/bench/bench_test.go
@@ -451,6 +451,21 @@ func BenchmarkAccumRowInt32s(b *testing.B) {
 	}
 }
 
+// StoreRowFloat32s adds alpha*x into one row of a two-dimensional slice.
+func BenchmarkStoreRowFloat32s(b *testing.B) {
+	for _, n := range benchSizes {
+		b.Run(fmt.Sprintf("%d", n), func(b *testing.B) {
+			x := make([]float32, n)
+			c := make([]float32, 2*n)
+			setBytes(b, n, 4, 3)
+			b.ResetTimer()
+			for b.Loop() {
+				StoreRowFloat32s(c, x, 2, 1, n)
+			}
+		})
+	}
+}
+
 func BenchmarkMinUint16s(b *testing.B) {
 	for _, n := range benchSizes {
 		b.Run(fmt.Sprintf("%d", n), func(b *testing.B) {

diff --git a/bench/ops.go b/bench/ops.go
@@ -332,3 +332,9 @@ func HardSigmoidFloat32s(dst, x []float32) {
 		dst[i] = t / 6
 	}
 }
+
+func StoreRowFloat32s(c, x []float32, alpha float32, row, ldc int) {
+	for j := range x {
+		c[row*ldc+j] += alpha * x[j]
+	}
+}
diff --git a/bench/ops_simd.go b/bench/ops_simd.go
@@ -986,6 +986,26 @@ func HardSigmoidFloat32s(dst, x []float32) {
 	}
 }
 
+func StoreRowFloat32s(c, x []float32, alpha float32, row, ldc int) {
+	_vcAFloat32s46 := simd.BroadcastFloat32s(alpha)
+	if _loopvecOverlap(c, x, 0+(min(0, row*ldc)), len(x)+(max(0, row*ldc)), 0, len(x)) {
+		for j := range x {
+			c[row*ldc+j] += alpha * x[j]
+		}
+	} else {
+		if len(x) > 0 {
+			_ = c[len(x)+(row*ldc)-1]
+			_ = x[len(x)-1]
+			for _i := 0; _i < len(x); {
+				_v1, _n := simd.LoadFloat32sPart(x[_i:len(x)])
+				_v2, _ := simd.LoadFloat32sPart(c[_i+(row*ldc):])
+				_v1.MulAdd(_vcAFloat32s46, _v2).StorePart(c[_i+(row*ldc) : len(x)+(row*ldc)])
+				_i += _n
+			}
+		}
+	}
+}
+
 func _loopvecOverlap[T any](a, b []T, window ...int) bool {
 	aLo, aHi, bLo, bHi := 0, len(a), 0, len(b)
 	if len(window) == 4 {

diff --git a/go.mod b/go.mod
@@ -3,7 +3,7 @@ module github.com/mauri870/loopvec
 go 1.27.1
 
 require (
-	golang.org/x/tools v0.51.0
+	golang.org/x/tools v0.52.1-0.20261030190145-0f433775b36d
 	rsc.io/script v0.0.2
 )
 
@@ -207,10 +207,10 @@ require (
 	go.uber.org/zap v1.27.0 // indirect
 	go.yaml.in/yaml/v3 v3.0.5 // indirect
 	golang.org/x/exp/typeparams v0.0.0-20260811152304-ee035b5b010f // indirect
-	golang.org/x/mod v0.41.0 // indirect
-	golang.org/x/sync v0.23.0 // indirect
-	golang.org/x/sys v0.48.0 // indirect
-	golang.org/x/telemetry v0.0.0-20260924152758-ed294f943157 // indirect
+	golang.org/x/mod v0.42.0 // indirect
+	golang.org/x/sync v0.24.0 // indirect
+	golang.org/x/sys v0.49.0 // indirect
+	golang.org/x/telemetry v0.0.0-20261009151841-97e8ea77aa2a // indirect
 	golang.org/x/text v0.41.0 // indirect
 	google.golang.org/protobuf v1.36.12 // indirect
 	gopkg.in/ini.v1 v1.67.0 // indirect

diff --git a/go.sum b/go.sum
@@ -688,8 +688,8 @@ golang.org/x/mod v0.4.1/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.6.0-dev.0.20220106191415-9b9b3d81d5e3/go.mod h1:3p9vT2HGsQu2K1YbXdKPJLVgG5VJdoTa1poYQBtP1AY=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
 golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
-golang.org/x/mod v0.41.0 h1:qJmnOUb4YB+FsEuM3HcWucdZASCPGhsX6uljO6pog0c=
-golang.org/x/mod v0.41.0/go.mod h1:Ek9pY8RKWXwsWvd3rQiHYtMqkjSUV+s1Rj7j4H5Ur6o=
+golang.org/x/mod v0.42.0 h1:ICeL3t2L30ljSPHHxDnR4fqVcBt/zR2zJAb9juavmQg=
+golang.org/x/mod v0.42.0/go.mod h1:u5fzIrRInkL8MaO1cbRkUHT64v303YIT5KEqpNr7jRs=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20181114220301-adae6a3d119a/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
@@ -724,8 +724,8 @@ golang.org/x/net v0.0.0-20210525063256-abc453219eb5/go.mod h1:9nx3DQGgdP8bBQD5qx
 golang.org/x/net v0.0.0-20211015210444-4f30a5c0130f/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
 golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
-golang.org/x/net v0.59.0 h1:5zfYln+w5XCxwrnMMJPufRgNoXEaGxl0wo5GqPXyues=
-golang.org/x/net v0.59.0/go.mod h1:2DA/G1UfVbCpQPeWTmMPGY7Cs2PkBkwu743bVX5PIVg=
+golang.org/x/net v0.61.0 h1:RR+6j/BTBCrggOLugxa+66R8FvoN6MHlzDlZIbN9YFw=
+golang.org/x/net v0.61.0/go.mod h1:WgDCOTH8iwtB66T4/GfI94AHo/hhdb7Hah9NDseQfiI=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
 golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
@@ -745,8 +745,8 @@ golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.23.0 h1:KameEIfc1IkluZyXWLn39Wd4tURc6GbCiISGiZm2bQk=
-golang.org/x/sync v0.23.0/go.mod h1:sUUOizhqBxiL6pEWpqNLUiaJn1ShEbZ6BBqskPbjZm0=
+golang.org/x/sync v0.24.0 h1:iqiDrGoDgyuvAKrhLQthUEzU/R378N78gXbBjxed7oA=
+golang.org/x/sync v0.24.0/go.mod h1:sUUOizhqBxiL6pEWpqNLUiaJn1ShEbZ6BBqskPbjZm0=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
@@ -790,10 +790,10 @@ golang.org/x/sys v0.0.0-20220114195835-da31bd327af9/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
-golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
-golang.org/x/telemetry v0.0.0-20260924152758-ed294f943157 h1:DftxASHKl6JolFPqoN+2WrFO53JvkHwRXvFqf8gsivA=
-golang.org/x/telemetry v0.0.0-20260924152758-ed294f943157/go.mod h1:i+ivNqjDnTF3WTElsdk5g9V5DTSBYgdNo7xTU9SDwYA=
+golang.org/x/sys v0.49.0 h1:XbzkgYJHdqh/8m2Uu0W/dQv8nktxx4BFHp1M0gROTXA=
+golang.org/x/sys v0.49.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
+golang.org/x/telemetry v0.0.0-20261009151841-97e8ea77aa2a h1:wnveMBKHwx8/nIb8WYT5P9vtefdXOvIWxzycCkc5n6Q=
+golang.org/x/telemetry v0.0.0-20261009151841-97e8ea77aa2a/go.mod h1:i+ivNqjDnTF3WTElsdk5g9V5DTSBYgdNo7xTU9SDwYA=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
@@ -857,8 +857,8 @@ golang.org/x/tools v0.1.1-0.20210302220138-2ac05c832e1a/go.mod h1:9bzcO0MWcOuT0t
 golang.org/x/tools v0.1.10/go.mod h1:Uh6Zz+xoGYZom868N8YTex3t7RhtHDBrE8Gzo9bV56E=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
 golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
-golang.org/x/tools v0.51.0 h1:k4Xc/1Om9jwkBJBo4NVLMSARBoWtK10mx+W5BnXCeAI=
-golang.org/x/tools v0.51.0/go.mod h1:9eEncMayCV6zRMGhR5eZEC2iBx98qWcF1HZ9Z7wJOoA=
+golang.org/x/tools v0.52.1-0.20261030190145-0f433775b36d h1:F5ot9G6RM6pgx3TTdKF6IZa2nocit4tcsrVQlq4Zh5w=
+golang.org/x/tools v0.52.1-0.20261030190145-0f433775b36d/go.mod h1:ItcP5UNaVGG+Yc4eIYmaFLNJ4soEopkx5Y2d4lcEurs=
 golang.org/x/tools/go/expect v0.1.1-deprecated h1:jpBZDwmgPhXsKZC6WhL20P4b/wmnpsEAGHaNy0n/rJM=
 golang.org/x/tools/go/expect v0.1.1-deprecated/go.mod h1:eihoPOH+FgIqa3FpoTwguz/bVUSGBlGQU67vpBeOrBY=
 golang.org/x/tools/go/packages/packagestest v0.1.1-deprecated h1:1h2MnaIAIXISqTFKdENegdpAgUXz6NrPEsbIeWaBRvM=

diff --git a/internal/loopir/caps_gen.go b/internal/loopir/caps_gen.go
diff --git a/internal/loopir/ir.go b/internal/loopir/ir.go
@@ -166,9 +166,12 @@ type Loop struct {
 // Stmt is a statement of a loop body: a Store or a Let.
 type Stmt interface{ isStmt() }
 
-// Store writes Val to Dst[i].
+// Store writes Val to Dst[i+Off]. Off is source text for an integer expression
+// that is the same on every iteration, "" for zero, as in Load. Every store to
+// one slice is at the same offset, so no two iterations write the same element.
 type Store struct {
 	Dst *Ref
+	Off string
 	Val Value
 }
 
@@ -207,9 +210,10 @@ type Value interface{ isValue() }
 
 // Load reads Ref[i+Off]. Off is source text for an integer expression that is the
 // same on every iteration, "" for zero. A slice that is also stored in the loop is
-// read only at a constant positive offset: iteration i then reads the element a
-// later iteration writes, and the vector loop, which loads the chunk before any
-// store of the body, sees the same old value.
+// read only at the offset it is stored at, or a constant positive distance past
+// it: iteration i then reads the element a later iteration writes, and the vector
+// loop, which loads the chunk before any store of the body, sees the same old
+// value.
 // FromRange is set when the source is the range value variable, which holds the
 // element as it was when the iteration began: a store to the same slice earlier in
 // the body does not change it.