[llvm] [AArch64][GlobalISel] Prevented llvm.aarch64.neon.saddlp/uaddlp fallback (PR #160883)

[Joshua Rodriguez via llvm-commits]

https://github.com/JoshdRod updated https://github.com/llvm/llvm-project/pull/160883

>From d2f7fba049f5191736783035a658e380e2c4755b Mon Sep 17 00:00:00 2001
From: Josh Rodriguez <josh.rodriguez at arm.com>
Date: Fri, 26 Sep 2025 10:40:26 +0000
Subject: [PATCH 1/2] [AArch64][GlobalISel] Prevented
 llvm.aarch64.neon.saddlp/uaddlp fallback

Prevented fallback on G_SADDLP/G_UADDLP instructions that return one-element i64 vectors, caused due to incorrect Register Bank Selection.
---
 llvm/lib/Target/AArch64/GISel/AArch64RegisterBankInfo.cpp | 4 ++++
 llvm/test/CodeGen/AArch64/arm64-vadd.ll                   | 5 +----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/AArch64/GISel/AArch64RegisterBankInfo.cpp b/llvm/lib/Target/AArch64/GISel/AArch64RegisterBankInfo.cpp
index f90bcc7a77cdf..830a35bbeb494 100644
--- a/llvm/lib/Target/AArch64/GISel/AArch64RegisterBankInfo.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64RegisterBankInfo.cpp
@@ -590,6 +590,8 @@ bool AArch64RegisterBankInfo::onlyDefinesFP(const MachineInstr &MI,
                                             unsigned Depth) const {
   switch (MI.getOpcode()) {
   case AArch64::G_DUP:
+  case AArch64::G_SADDLP:
+  case AArch64::G_UADDLP:
   case TargetOpcode::G_SITOFP:
   case TargetOpcode::G_UITOFP:
   case TargetOpcode::G_EXTRACT_VECTOR_ELT:
@@ -798,6 +800,8 @@ AArch64RegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
     if (Ty.isVector())
       OpRegBankIdx[Idx] = PMI_FirstFPR;
     else if (isPreISelGenericFloatingPointOpcode(Opc) ||
+             (MO.isDef() && onlyDefinesFP(MI, MRI, TRI)) ||
+             (MO.isUse() && onlyUsesFP(MI, MRI, TRI)) ||
              Ty.getSizeInBits() > 64)
       OpRegBankIdx[Idx] = PMI_FirstFPR;
     else
diff --git a/llvm/test/CodeGen/AArch64/arm64-vadd.ll b/llvm/test/CodeGen/AArch64/arm64-vadd.ll
index 11fb73237da07..e3c80256feea0 100644
--- a/llvm/test/CodeGen/AArch64/arm64-vadd.ll
+++ b/llvm/test/CodeGen/AArch64/arm64-vadd.ll
@@ -1,9 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
 ; RUN: llc < %s -mtriple=arm64-eabi | FileCheck %s --check-prefixes=CHECK,CHECK-SD
-; RUN: llc < %s -mtriple=arm64-eabi -global-isel -global-isel-abort=2 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-GI
-
-; CHECK-GI:       warning: Instruction selection used fallback path for saddlp1d
-; CHECK-GI-NEXT:  warning: Instruction selection used fallback path for uaddlp1d
+; RUN: llc < %s -mtriple=arm64-eabi -global-isel | FileCheck %s --check-prefixes=CHECK,CHECK-GI
 
 define <8 x i8> @addhn8b(ptr %A, ptr %B) nounwind {
 ; CHECK-LABEL: addhn8b:

>From 28b34fb762f2306873f61fbd49a02511548e613c Mon Sep 17 00:00:00 2001
From: Josh Rodriguez <josh.rodriguez at arm.com>
Date: Tue, 7 Oct 2025 09:25:17 +0000
Subject: [PATCH 2/2] [AArch64][GlobalISel] Added mir test for saddlp/uaddlp
 intrinsics

---
 .../AArch64/arm64-saddlp1d-uaddlp1d.mir       | 50 +++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 llvm/test/CodeGen/AArch64/arm64-saddlp1d-uaddlp1d.mir

diff --git a/llvm/test/CodeGen/AArch64/arm64-saddlp1d-uaddlp1d.mir b/llvm/test/CodeGen/AArch64/arm64-saddlp1d-uaddlp1d.mir
new file mode 100644
index 0000000000000..074f75ab8a5f0
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/arm64-saddlp1d-uaddlp1d.mir
@@ -0,0 +1,50 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 6
+# RUN: llc -mtriple=aarch64 -run-pass=regbankselect -verify-machineinstrs %s -o - | FileCheck %s
+
+---
+name:            saddlp1d
+legalized:       true
+regBankSelected: false
+tracksRegLiveness: true
+body:             |
+  bb.1.entry:
+    liveins: $x0
+
+    ; CHECK-LABEL: name: saddlp1d
+    ; CHECK: liveins: $x0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr(p0) = COPY $x0
+    ; CHECK-NEXT: [[LOAD:%[0-9]+]]:fpr(<2 x s32>) = G_LOAD [[COPY]](p0) :: (load (<2 x s32>))
+    ; CHECK-NEXT: [[SADDLP:%[0-9]+]]:fpr(s64) = G_SADDLP [[LOAD]]
+    ; CHECK-NEXT: $d0 = COPY [[SADDLP]](s64)
+    ; CHECK-NEXT: RET_ReallyLR implicit $d0
+    %0:_(p0) = COPY $x0
+    %1:_(<2 x s32>) = G_LOAD %0(p0) :: (load (<2 x s32>))
+    %2:_(s64) = G_SADDLP %1
+    $d0 = COPY %2(s64)
+    RET_ReallyLR implicit $d0
+...
+---
+name:            uaddlp1d
+legalized:       true
+regBankSelected: false
+failedISel:      false
+tracksRegLiveness: true
+body:             |
+  bb.1.entry:
+    liveins: $x0
+
+    ; CHECK-LABEL: name: uaddlp1d
+    ; CHECK: liveins: $x0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr(p0) = COPY $x0
+    ; CHECK-NEXT: [[LOAD:%[0-9]+]]:fpr(<2 x s32>) = G_LOAD [[COPY]](p0) :: (load (<2 x s32>))
+    ; CHECK-NEXT: [[UADDLP:%[0-9]+]]:fpr(s64) = G_UADDLP [[LOAD]]
+    ; CHECK-NEXT: $d0 = COPY [[UADDLP]](s64)
+    ; CHECK-NEXT: RET_ReallyLR implicit $d0
+    %0:_(p0) = COPY $x0
+    %1:_(<2 x s32>) = G_LOAD %0(p0) :: (load (<2 x s32>))
+    %2:_(s64) = G_UADDLP %1
+    $d0 = COPY %2(s64)
+    RET_ReallyLR implicit $d0
+...