[llvm] [Hexagon] Lowering saturating subtraction (PR #158726)
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Mon Sep 15 12:53:29 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-hexagon
Author: Alexey Karyakin (quic-akaryaki)
<details>
<summary>Changes</summary>
Saturating arithmetic can be expressed by llvm.uadd/usub.sat generic intrinsics.
---
Full diff: https://github.com/llvm/llvm-project/pull/158726.diff
3 Files Affected:
- (modified) llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp (+4)
- (modified) llvm/lib/Target/Hexagon/HexagonPatternsHVX.td (+15)
- (added) llvm/test/CodeGen/Hexagon/vsubsat.ll (+99)
``````````diff
diff --git a/llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp b/llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp
index f1fa40c1b9036..adfcddf035011 100644
--- a/llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonISelLoweringHVX.cpp
@@ -208,6 +208,8 @@ HexagonTargetLowering::initializeHVXLowering() {
setOperationAction(ISD::SPLAT_VECTOR, T, Legal);
setOperationAction(ISD::UADDSAT, T, Legal);
setOperationAction(ISD::SADDSAT, T, Legal);
+ setOperationAction(ISD::USUBSAT, T, Legal);
+ setOperationAction(ISD::SSUBSAT, T, Legal);
if (T != ByteV) {
setOperationAction(ISD::SIGN_EXTEND_VECTOR_INREG, T, Legal);
setOperationAction(ISD::ZERO_EXTEND_VECTOR_INREG, T, Legal);
@@ -302,6 +304,8 @@ HexagonTargetLowering::initializeHVXLowering() {
setOperationAction(ISD::UADDSAT, T, Legal);
setOperationAction(ISD::SADDSAT, T, Legal);
setOperationAction(ISD::SUB, T, Legal);
+ setOperationAction(ISD::USUBSAT, T, Legal);
+ setOperationAction(ISD::SSUBSAT, T, Legal);
setOperationAction(ISD::MUL, T, Custom);
setOperationAction(ISD::MULHS, T, Custom);
setOperationAction(ISD::MULHU, T, Custom);
diff --git a/llvm/lib/Target/Hexagon/HexagonPatternsHVX.td b/llvm/lib/Target/Hexagon/HexagonPatternsHVX.td
index fb2ef59d99ef1..1637b91f1fa12 100644
--- a/llvm/lib/Target/Hexagon/HexagonPatternsHVX.td
+++ b/llvm/lib/Target/Hexagon/HexagonPatternsHVX.td
@@ -441,6 +441,21 @@ let Predicates = [UseHVX] in {
def: OpR_RR_pat_sat<V6_vaddwsat_dv, saddsat, VecPI32, HWI32>;
}
+let Predicates = [UseHVX] in {
+ def: OpR_RR_pat_sat<V6_vsububsat, usubsat, VecI8, HVI8>;
+ def: OpR_RR_pat_sat<V6_vsubuhsat, usubsat, VecI16, HVI16>;
+ def: OpR_RR_pat_sat<V6_vsubuwsat, usubsat, VecI32, HVI32>;
+ def: OpR_RR_pat_sat<V6_vsubbsat, ssubsat, VecI8, HVI8>;
+ def: OpR_RR_pat_sat<V6_vsubhsat, ssubsat, VecI16, HVI16>;
+ def: OpR_RR_pat_sat<V6_vsubwsat, ssubsat, VecI32, HVI32>;
+ def: OpR_RR_pat_sat<V6_vsububsat_dv, usubsat, VecPI8, HWI8>;
+ def: OpR_RR_pat_sat<V6_vsubuhsat_dv, usubsat, VecPI16, HWI16>;
+ def: OpR_RR_pat_sat<V6_vsubuwsat_dv, usubsat, VecPI32, HWI32>;
+ def: OpR_RR_pat_sat<V6_vsubbsat_dv, ssubsat, VecPI8, HWI8>;
+ def: OpR_RR_pat_sat<V6_vsubhsat_dv, ssubsat, VecPI16, HWI16>;
+ def: OpR_RR_pat_sat<V6_vsubwsat_dv, ssubsat, VecPI32, HWI32>;
+}
+
// For now, we always deal with vector floating point in SF mode.
class OpR_RR_pat_conv<InstHexagon MI, PatFrag Op, ValueType ResType,
PatFrag RsPred, PatFrag RtPred = RsPred>
diff --git a/llvm/test/CodeGen/Hexagon/vsubsat.ll b/llvm/test/CodeGen/Hexagon/vsubsat.ll
new file mode 100644
index 0000000000000..bb65aff166e23
--- /dev/null
+++ b/llvm/test/CodeGen/Hexagon/vsubsat.ll
@@ -0,0 +1,99 @@
+; RUN: llc -march=hexagon -mattr=+hvxv73,+hvx-length128b < %s | FileCheck %s
+
+;; Saturating subtraction.
+
+; CHECK-LABEL: vsububsat
+; CHECK: v[[#]].ub = vsub(v[[#]].ub,v[[#]].ub):sat
+define dso_local <128 x i8> @vsububsat(<128 x i8> %x, <128 x i8> %y) {
+entry:
+ %0 = tail call <128 x i8> @llvm.usub.sat.v128i8(<128 x i8> %x, <128 x i8> %y)
+ ret <128 x i8> %0
+}
+
+; CHECK-LABEL: vsubuhsat
+; CHECK: v[[#]].uh = vsub(v[[#]].uh,v[[#]].uh):sat
+define dso_local <64 x i16> @vsubuhsat(<64 x i16> %x, <64 x i16> %y) {
+entry:
+ %0 = tail call <64 x i16> @llvm.usub.sat.v64i16(<64 x i16> %x, <64 x i16> %y)
+ ret <64 x i16> %0
+}
+
+; CHECK-LABEL: vsubuwsat
+; CHECK: v[[#]].uw = vsub(v[[#]].uw,v[[#]].uw):sat
+define dso_local <32 x i32> @vsubuwsat(<32 x i32> %x, <32 x i32> %y) {
+entry:
+ %0 = tail call <32 x i32> @llvm.usub.sat.v32i32(<32 x i32> %x, <32 x i32> %y)
+ ret <32 x i32> %0
+}
+
+; CHECK-LABEL: vsubbsat
+; CHECK: v[[#]].b = vsub(v[[#]].b,v[[#]].b):sat
+define dso_local <128 x i8> @vsubbsat(<128 x i8> %x, <128 x i8> %y) {
+entry:
+ %0 = tail call <128 x i8> @llvm.ssub.sat.v128i8(<128 x i8> %x, <128 x i8> %y)
+ ret <128 x i8> %0
+}
+
+; CHECK-LABEL: vsubhsat
+; CHECK: v[[#]].h = vsub(v[[#]].h,v[[#]].h):sat
+define dso_local <64 x i16> @vsubhsat(<64 x i16> %x, <64 x i16> %y) {
+entry:
+ %0 = tail call <64 x i16> @llvm.ssub.sat.v64i16(<64 x i16> %x, <64 x i16> %y)
+ ret <64 x i16> %0
+}
+
+; CHECK-LABEL: vsubwsat
+; CHECK: v[[#]].w = vsub(v[[#]].w,v[[#]].w):sat
+define dso_local <32 x i32> @vsubwsat(<32 x i32> %x, <32 x i32> %y) {
+entry:
+ %0 = tail call <32 x i32> @llvm.ssub.sat.v32i32(<32 x i32> %x, <32 x i32> %y)
+ ret <32 x i32> %0
+}
+
+; CHECK-LABEL: vsububsat_dv
+; CHECK: v[[#]]:[[#]].ub = vsub(v[[#]]:[[#]].ub,v[[#]]:[[#]].ub):sat
+define dso_local <256 x i8> @vsububsat_dv(<256 x i8> %x, <256 x i8> %y) {
+entry:
+ %0 = tail call <256 x i8> @llvm.usub.sat.v256i8(<256 x i8> %x, <256 x i8> %y)
+ ret <256 x i8> %0
+}
+
+; CHECK-LABEL: vsubuhsat_dv
+; CHECK: v[[#]]:[[#]].uh = vsub(v[[#]]:[[#]].uh,v[[#]]:[[#]].uh):sat
+define dso_local <128 x i16> @vsubuhsat_dv(<128 x i16> %x, <128 x i16> %y) {
+entry:
+ %0 = tail call <128 x i16> @llvm.usub.sat.v128i16(<128 x i16> %x, <128 x i16> %y)
+ ret <128 x i16> %0
+}
+
+; CHECK-LABEL: vsubuwsat_dv
+; CHECK: v[[#]]:[[#]].uw = vsub(v[[#]]:[[#]].uw,v[[#]]:[[#]].uw):sat
+define dso_local <64 x i32> @vsubuwsat_dv(<64 x i32> %x, <64 x i32> %y) {
+entry:
+ %0 = tail call <64 x i32> @llvm.usub.sat.v64i32(<64 x i32> %x, <64 x i32> %y)
+ ret <64 x i32> %0
+}
+
+; CHECK-LABEL: vsubbsat_dv
+; CHECK: v[[#]]:[[#]].b = vsub(v[[#]]:[[#]].b,v[[#]]:[[#]].b):sat
+define dso_local <256 x i8> @vsubbsat_dv(<256 x i8> %x, <256 x i8> %y) {
+entry:
+ %0 = tail call <256 x i8> @llvm.ssub.sat.v256i8(<256 x i8> %x, <256 x i8> %y)
+ ret <256 x i8> %0
+}
+
+; CHECK-LABEL: vsubhsat_dv
+; CHECK: v[[#]]:[[#]].h = vsub(v[[#]]:[[#]].h,v[[#]]:[[#]].h):sat
+define dso_local <128 x i16> @vsubhsat_dv(<128 x i16> %x, <128 x i16> %y) {
+entry:
+ %0 = tail call <128 x i16> @llvm.ssub.sat.v128i16(<128 x i16> %x, <128 x i16> %y)
+ ret <128 x i16> %0
+}
+
+; CHECK-LABEL: vsubwsat_dv
+; CHECK: v[[#]]:[[#]].w = vsub(v[[#]]:[[#]].w,v[[#]]:[[#]].w):sat
+define dso_local <64 x i32> @vsubwsat_dv(<64 x i32> %x, <64 x i32> %y) {
+entry:
+ %0 = tail call <64 x i32> @llvm.ssub.sat.v64i32(<64 x i32> %x, <64 x i32> %y)
+ ret <64 x i32> %0
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/158726
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