[llvm] [GlobalISel] Adding G_AND identity combine (PR #150831)

[Dávid Ferenc Szabó via llvm-commits]

https://github.com/dfszabo created https://github.com/llvm/llvm-project/pull/150831

Combine G_AND(X, -1) to X.

>From 510123e430fe6dc98d3ef9cf17ee3195cb209bfd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?D=C3=A1vid=20Ferenc=20Szab=C3=B3?=
 <szabodavidferenc at gmail.com>
Date: Sun, 27 Jul 2025 16:03:28 +0200
Subject: [PATCH] [GlobalISel] Adding G_AND identity combine

Combine G_AND(X, -1) to X.
---
 .../include/llvm/Target/GlobalISel/Combine.td |  9 ++++++++-
 .../prelegalizercombiner-trivial-arith.mir    | 20 +++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Target/GlobalISel/Combine.td b/llvm/include/llvm/Target/GlobalISel/Combine.td
index fc81ab76dc72d..236402dfc0f1b 100644
--- a/llvm/include/llvm/Target/GlobalISel/Combine.td
+++ b/llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -566,6 +566,12 @@ def right_identity_one_int: GICombineRule<
   (apply (GIReplaceReg $dst, $x))
 >;
 
+def right_identity_neg_one_int: GICombineRule<
+  (defs root:$dst),
+  (match (G_AND $dst, $x, -1)),
+  (apply (GIReplaceReg $dst, $x))
+>;
+
 def right_identity_one_fp: GICombineRule<
   (defs root:$dst),
   (match (G_FMUL $dst, $x, $y):$root,
@@ -2003,7 +2009,8 @@ def identity_combines : GICombineGroup<[select_same_val, right_identity_zero,
                                         trunc_lshr_buildvector_fold,
                                         bitcast_bitcast_fold, fptrunc_fpext_fold,
                                         right_identity_neg_zero_fp,
-                                        right_identity_neg_one_fp]>;
+                                        right_identity_neg_one_fp,
+                                        right_identity_neg_one_int]>;
 
 def const_combines : GICombineGroup<[constant_fold_fp_ops, const_ptradd_to_i2p,
                                      overlapping_and, mulo_by_2, mulo_by_0,
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir b/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
index d36b382672e60..1e9f1e905db7c 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
@@ -165,6 +165,26 @@ body:             |
 
 ...
 
+---
+name:            right_ident_and
+tracksRegLiveness: true
+body:             |
+  bb.1.entry:
+    liveins: $w0
+    ; Fold (x & -1) -> x
+    ; CHECK-LABEL: name: right_ident_and
+    ; CHECK: liveins: $w0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %x:_(s32) = COPY $w0
+    ; CHECK-NEXT: $w0 = COPY %x(s32)
+    ; CHECK-NEXT: RET_ReallyLR implicit $w0
+    %x:_(s32) = COPY $w0
+    %cst:_(s32) = G_CONSTANT i32 -1
+    %op:_(s32) = G_AND %x(s32), %cst
+    $w0 = COPY %op(s32)
+    RET_ReallyLR implicit $w0
+
+...
 ---
 name:            right_ident_or
 tracksRegLiveness: true