[llvm] [AArch64][GlobalISel] Expand abs.v4i8 to v4i16 and abs.v2s16 to v2s32 (PR #81231)

[Dhruv Chawla via llvm-commits]

https://github.com/dc03-work created https://github.com/llvm/llvm-project/pull/81231

GISel was currently falling back to SDAG for these functions, and this matches the way SDAG currently generates code for these functions.

>From 733847a5641a1b156d795c6cd046c15170f7d083 Mon Sep 17 00:00:00 2001
From: Dhruv Chawla <dhruvc at nvidia.com>
Date: Thu, 8 Feb 2024 09:44:46 +0530
Subject: [PATCH] [AArch64][GlobalISel] Expand abs.v4i8 to v4i16 and abs.v2s16
 to v2s32

GISel was currently falling back to SDAG for these functions, and this matches
the way SDAG currently generates code for these functions.
---
 llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp | 6 ++++++
 llvm/test/CodeGen/AArch64/abs.ll                       | 3 ---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp b/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
index cbf5655706e694..5dc3ebf09d17e5 100644
--- a/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
@@ -993,6 +993,12 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
     ABSActions
         .legalFor({s32, s64});
   ABSActions.legalFor(PackedVectorAllTypeList)
+      .widenScalarIf(
+          [=](const LegalityQuery &Query) { return Query.Types[0] == v4s8; },
+          [=](const LegalityQuery &Query) { return std::make_pair(0, v4s16); })
+      .widenScalarIf(
+          [=](const LegalityQuery &Query) { return Query.Types[0] == v2s16; },
+          [=](const LegalityQuery &Query) { return std::make_pair(0, v2s32); })
       .clampNumElements(0, v8s8, v16s8)
       .clampNumElements(0, v4s16, v8s16)
       .clampNumElements(0, v2s32, v4s32)
diff --git a/llvm/test/CodeGen/AArch64/abs.ll b/llvm/test/CodeGen/AArch64/abs.ll
index 934aae9ec74c03..260631c414eddc 100644
--- a/llvm/test/CodeGen/AArch64/abs.ll
+++ b/llvm/test/CodeGen/AArch64/abs.ll
@@ -2,9 +2,6 @@
 ; RUN: llc -mtriple=aarch64-none-linux-gnu %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-SD
 ; RUN: llc -mtriple=aarch64-none-linux-gnu -global-isel -global-isel-abort=2 %s -o - 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-GI
 
-; CHECK-GI:         warning: Instruction selection used fallback path for abs_v4i8
-; CHECK-GI-NEXT:    warning: Instruction selection used fallback path for abs_v2i16
-
 ; ===== Legal Scalars =====
 
 define i8 @abs_i8(i8 %a){