[llvm] webassembly: recognize saturating truncation (PR #155470)
Folkert de Vries via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 6 11:42:42 PDT 2025
https://github.com/folkertdev updated https://github.com/llvm/llvm-project/pull/155470
>From eb7f06daff3ce9141eb99cdab529f98ad62005eb Mon Sep 17 00:00:00 2001
From: Folkert de Vries <folkert at folkertdev.nl>
Date: Tue, 26 Aug 2025 20:56:40 +0200
Subject: [PATCH] webassembly: recognize saturating truncation
and turn it into `narrow_TYPE_s`
---
.../WebAssembly/WebAssemblyInstrSIMD.td | 43 +++++++++
.../WebAssembly/saturating-truncation.ll | 87 +++++++++++++++++++
2 files changed, 130 insertions(+)
create mode 100644 llvm/test/CodeGen/WebAssembly/saturating-truncation.ll
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
index d8948ad2df037..4f35ab572bd9f 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
@@ -1445,6 +1445,49 @@ def : Pat<(v16i8 (wasm_narrow_u (v8i16 V128:$left), (v8i16 V128:$right))),
def : Pat<(v8i16 (wasm_narrow_u (v4i32 V128:$left), (v4i32 V128:$right))),
(NARROW_U_I16x8 $left, $right)>;
+// Recognize a saturating truncation and convert into the corresponding
+// narrow_TYPE_s or narrow_TYPE_u instruction.
+multiclass SignedSaturatingTruncate<ValueType input, ValueType output,
+ Instruction narrow, int minval,
+ int maxval, int mask> {
+ def : Pat<
+ (output (wasm_narrow_u
+ (and (smin (smax (input V128:$a), (splat_vector (i32 minval))),
+ (splat_vector (i32 maxval))), (splat_vector (i32 mask))),
+ (and (smin (smax (input V128:$b), (splat_vector (i32 minval))),
+ (splat_vector (i32 maxval))), (splat_vector (i32 mask)))
+ )),
+ (narrow V128:$a, V128:$b)
+ >;
+
+ def : Pat<
+ (output (wasm_narrow_u
+ (and (smax (smin (input V128:$a), (splat_vector (i32 maxval))),
+ (splat_vector (i32 minval))), (splat_vector (i32 mask))),
+ (and (smax (smin (input V128:$b), (splat_vector (i32 maxval))),
+ (splat_vector (i32 minval))), (splat_vector (i32 mask)))
+ )),
+ (narrow V128:$a, V128:$b)
+ >;
+}
+
+defm : SignedSaturatingTruncate<v8i16, v16i8, NARROW_S_I8x16, -128, 127, 0xFF>;
+defm : SignedSaturatingTruncate<v4i32, v8i16, NARROW_S_I16x8, -32768, 32767, 0xFFFF>;
+
+multiclass UnsignedSaturatingTruncate<ValueType input, ValueType output,
+ Instruction narrow, int maxval> {
+ def : Pat<
+ (output (wasm_narrow_u
+ (umin (input V128:$a), (splat_vector (i32 maxval))),
+ (umin (input V128:$b), (splat_vector (i32 maxval)))
+ )),
+ (narrow V128:$a, V128:$b)
+ >;
+}
+
+defm : UnsignedSaturatingTruncate<v8i16, v16i8, NARROW_U_I8x16, 0xFF>;
+defm : UnsignedSaturatingTruncate<v4i32, v8i16, NARROW_U_I16x8, 0xFFFF>;
+
// Bitcasts are nops
// Matching bitcast t1 to t1 causes strange errors, so avoid repeating types
foreach t1 = AllVecs in
diff --git a/llvm/test/CodeGen/WebAssembly/saturating-truncation.ll b/llvm/test/CodeGen/WebAssembly/saturating-truncation.ll
new file mode 100644
index 0000000000000..f3f3ba9b268d7
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/saturating-truncation.ll
@@ -0,0 +1,87 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+
+; RUN: llc < %s -verify-machineinstrs -mattr=+simd128 | FileCheck %s
+
+target triple = "wasm32-unknown-unknown"
+
+declare <8 x i32> @llvm.smin.v8i32(<8 x i32>, <8 x i32>) #2
+declare <8 x i32> @llvm.smax.v8i32(<8 x i32>, <8 x i32>) #2
+
+define <16 x i8> @i16_signed(<8 x i16> %a, <8 x i16> %b) {
+; CHECK-LABEL: i16_signed:
+; CHECK: .functype i16_signed (v128, v128) -> (v128)
+; CHECK-NEXT: # %bb.0: # %bb2
+; CHECK-NEXT: local.get 0
+; CHECK-NEXT: local.get 1
+; CHECK-NEXT: i8x16.narrow_i16x8_s
+; CHECK-NEXT: # fallthrough-return
+bb2:
+ %0 = shufflevector <8 x i16> %a, <8 x i16> %b, <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>
+ %1 = tail call <16 x i16> @llvm.smax.v16i16(<16 x i16> %0, <16 x i16> splat (i16 -128))
+ %2 = tail call <16 x i16> @llvm.smin.v16i16(<16 x i16> %1, <16 x i16> splat (i16 127))
+ %3 = trunc nsw <16 x i16> %2 to <16 x i8>
+ ret <16 x i8> %3
+ ret <16 x i8> %3
+}
+
+define <8 x i16> @i32_signed(<4 x i32> %a, <4 x i32> %b) {
+; CHECK-LABEL: i32_signed:
+; CHECK: .functype i32_signed (v128, v128) -> (v128)
+; CHECK-NEXT: # %bb.0: # %bb2
+; CHECK-NEXT: local.get 0
+; CHECK-NEXT: local.get 1
+; CHECK-NEXT: i16x8.narrow_i32x4_s
+; CHECK-NEXT: # fallthrough-return
+bb2:
+ %0 = shufflevector <4 x i32> %a, <4 x i32> %b, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+ %1 = tail call <8 x i32> @llvm.smax.v8i32(<8 x i32> %0, <8 x i32> splat (i32 -32768))
+ %2 = tail call <8 x i32> @llvm.smin.v8i32(<8 x i32> %1, <8 x i32> splat (i32 32767))
+ %3 = trunc nsw <8 x i32> %2 to <8 x i16>
+ ret <8 x i16> %3
+}
+
+define <8 x i16> @i32_signed_flipped(<4 x i32> %a, <4 x i32> %b) {
+; CHECK-LABEL: i32_signed_flipped:
+; CHECK: .functype i32_signed_flipped (v128, v128) -> (v128)
+; CHECK-NEXT: # %bb.0: # %bb2
+; CHECK-NEXT: local.get 0
+; CHECK-NEXT: local.get 1
+; CHECK-NEXT: i16x8.narrow_i32x4_s
+; CHECK-NEXT: # fallthrough-return
+bb2:
+ %0 = shufflevector <4 x i32> %a, <4 x i32> %b, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+ %1 = tail call <8 x i32> @llvm.smin.v8i32(<8 x i32> splat (i32 32767), <8 x i32> %0)
+ %2 = tail call <8 x i32> @llvm.smax.v8i32(<8 x i32> splat (i32 -32768), <8 x i32> %1)
+ %3 = trunc nsw <8 x i32> %2 to <8 x i16>
+ ret <8 x i16> %3
+}
+
+define <16 x i8> @i16_unsigned(<8 x i16> %a, <8 x i16> %b) {
+; CHECK-LABEL: i16_unsigned:
+; CHECK: .functype i16_unsigned (v128, v128) -> (v128)
+; CHECK-NEXT: # %bb.0: # %bb2
+; CHECK-NEXT: local.get 0
+; CHECK-NEXT: local.get 1
+; CHECK-NEXT: i8x16.narrow_i16x8_u
+; CHECK-NEXT: # fallthrough-return
+bb2:
+ %0 = shufflevector <8 x i16> %a, <8 x i16> %b, <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>
+ %1 = tail call <16 x i16> @llvm.umin.v16i16(<16 x i16> %0, <16 x i16> splat (i16 255))
+ %2 = trunc nuw <16 x i16> %1 to <16 x i8>
+ ret <16 x i8> %2
+}
+
+define <8 x i16> @i32_unsigned(<4 x i32> %a, <4 x i32> %b) {
+; CHECK-LABEL: i32_unsigned:
+; CHECK: .functype i32_unsigned (v128, v128) -> (v128)
+; CHECK-NEXT: # %bb.0: # %bb2
+; CHECK-NEXT: local.get 0
+; CHECK-NEXT: local.get 1
+; CHECK-NEXT: i16x8.narrow_i32x4_u
+; CHECK-NEXT: # fallthrough-return
+bb2:
+ %0 = shufflevector <4 x i32> %a, <4 x i32> %b, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+ %1 = tail call <8 x i32> @llvm.umin.v8i32(<8 x i32> %0, <8 x i32> splat (i32 65535))
+ %2 = trunc nsw <8 x i32> %1 to <8 x i16>
+ ret <8 x i16> %2
+}
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