[llvm] [DAG] Implement SDPatternMatch `m_Abs()` matcher (PR #144512)

[Rajveer Singh Bharadwaj via llvm-commits]

https://github.com/Rajveer100 updated https://github.com/llvm/llvm-project/pull/144512

>From 44570bc0c052da3622c90cabbd93f02ab02c51db Mon Sep 17 00:00:00 2001
From: Rajveer <rajveer.developer at icloud.com>
Date: Tue, 17 Jun 2025 17:13:12 +0530
Subject: [PATCH] [DAG] Implement SDPatternMatch `m_Abs()` matcher

Resolves #144474
---
 llvm/include/llvm/CodeGen/SDPatternMatch.h           |  4 ++++
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp        | 12 +++---------
 .../CodeGen/SelectionDAGPatternMatchTest.cpp         |  4 ++++
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/SDPatternMatch.h b/llvm/include/llvm/CodeGen/SDPatternMatch.h
index 2e3807a2dfffd..d413227c4d961 100644
--- a/llvm/include/llvm/CodeGen/SDPatternMatch.h
+++ b/llvm/include/llvm/CodeGen/SDPatternMatch.h
@@ -938,6 +938,10 @@ template <typename Opnd> inline UnaryOpc_match<Opnd> m_Trunc(const Opnd &Op) {
   return UnaryOpc_match<Opnd>(ISD::TRUNCATE, Op);
 }
 
+template <typename Opnd> inline UnaryOpc_match<Opnd> m_Abs(const Opnd &Op) {
+  return UnaryOpc_match<Opnd>(ISD::ABS, Op);
+}
+
 /// Match a zext or identity
 /// Allows to peek through optional extensions
 template <typename Opnd> inline auto m_ZExtOrSelf(const Opnd &Op) {
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 5d62ded171f4f..8d2d645bda8bd 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -11252,19 +11252,13 @@ SDValue DAGCombiner::foldABSToABD(SDNode *N, const SDLoc &DL) {
   if (N->getOpcode() == ISD::TRUNCATE)
     N = N->getOperand(0).getNode();
 
-  if (N->getOpcode() != ISD::ABS)
-    return SDValue();
-
   EVT VT = N->getValueType(0);
-  SDValue AbsOp1 = N->getOperand(0);
   SDValue Op0, Op1;
 
-  if (AbsOp1.getOpcode() != ISD::SUB)
+  if (!sd_match(N, m_Abs(m_Sub(m_Value(Op0), m_Value(Op1)))))
     return SDValue();
 
-  Op0 = AbsOp1.getOperand(0);
-  Op1 = AbsOp1.getOperand(1);
-
+  SDValue AbsOp0 = N->getOperand(0);
   unsigned Opc0 = Op0.getOpcode();
 
   // Check if the operands of the sub are (zero|sign)-extended.
@@ -11274,7 +11268,7 @@ SDValue DAGCombiner::foldABSToABD(SDNode *N, const SDLoc &DL) {
        Opc0 != ISD::SIGN_EXTEND_INREG)) {
     // fold (abs (sub nsw x, y)) -> abds(x, y)
     // Don't fold this for unsupported types as we lose the NSW handling.
-    if (AbsOp1->getFlags().hasNoSignedWrap() && hasOperation(ISD::ABDS, VT) &&
+    if (AbsOp0->getFlags().hasNoSignedWrap() && hasOperation(ISD::ABDS, VT) &&
         TLI.preferABDSToABSWithNSW(VT)) {
       SDValue ABD = DAG.getNode(ISD::ABDS, DL, VT, Op0, Op1);
       return DAG.getZExtOrTrunc(ABD, DL, SrcVT);
diff --git a/llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp b/llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp
index 1b590aa33bd86..2162588aadfdb 100644
--- a/llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp
+++ b/llvm/unittests/CodeGen/SelectionDAGPatternMatchTest.cpp
@@ -388,6 +388,8 @@ TEST_F(SelectionDAGPatternMatchTest, matchUnaryOp) {
   SDValue SExt = DAG->getNode(ISD::SIGN_EXTEND, DL, Int64VT, Op0);
   SDValue Trunc = DAG->getNode(ISD::TRUNCATE, DL, Int32VT, Op1);
 
+  SDValue Abs = DAG->getNode(ISD::ABS, DL, Int32VT, Op0);
+
   SDValue Sub = DAG->getNode(ISD::SUB, DL, Int32VT, Trunc, Op0);
   SDValue Neg = DAG->getNegative(Op0, DL, Int32VT);
   SDValue Not = DAG->getNOT(DL, Op0, Int32VT);
@@ -417,6 +419,8 @@ TEST_F(SelectionDAGPatternMatchTest, matchUnaryOp) {
   EXPECT_FALSE(sd_match(ZExt, m_SExtLike(m_Value())));
   EXPECT_TRUE(sd_match(Trunc, m_Trunc(m_Specific(Op1))));
 
+  EXPECT_TRUE(sd_match(Abs, m_Abs(m_Specific(Op0))));
+
   EXPECT_TRUE(sd_match(Neg, m_Neg(m_Value())));
   EXPECT_TRUE(sd_match(Not, m_Not(m_Value())));
   EXPECT_FALSE(sd_match(ZExt, m_Neg(m_Value())));