[llvm] [RISCV] Support P extension ABSW instruction. (PR #165047)

[Craig Topper via llvm-commits]

https://github.com/topperc created https://github.com/llvm/llvm-project/pull/165047

None

>From 55e9517c5e380b4c8b24ac2dc3ce9f7bd4f9cf80 Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper at sifive.com>
Date: Fri, 24 Oct 2025 14:18:39 -0700
Subject: [PATCH] [RISCV] Support P extension ABSW instruction.

---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp | 12 +++++++++++-
 llvm/lib/Target/RISCV/RISCVInstrInfoP.td    |  5 +++++
 llvm/test/CodeGen/RISCV/rv64p.ll            |  6 ++----
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 1c930acd9c4a0..be9d71c23f471 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -433,6 +433,8 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
   if (Subtarget.hasStdExtP() ||
       (Subtarget.hasVendorXCValu() && !Subtarget.is64Bit())) {
     setOperationAction(ISD::ABS, XLenVT, Legal);
+    if (Subtarget.is64Bit())
+      setOperationAction(ISD::ABS, MVT::i32, Custom);
   } else if (Subtarget.hasShortForwardBranchOpt()) {
     // We can use PseudoCCSUB to implement ABS.
     setOperationAction(ISD::ABS, XLenVT, Legal);
@@ -14816,8 +14818,16 @@ void RISCVTargetLowering::ReplaceNodeResults(SDNode *N,
     assert(N->getValueType(0) == MVT::i32 && Subtarget.is64Bit() &&
            "Unexpected custom legalisation");
 
+    if (Subtarget.hasStdExtP()) {
+      SDValue Src = DAG.getNode(ISD::ANY_EXTEND, DL, MVT::i64,
+                                N->getOperand(0));
+      SDValue Abs = DAG.getNode(RISCVISD::ABSW, DL, MVT::i64, Src);
+      Results.push_back(DAG.getNode(ISD::TRUNCATE, DL, MVT::i32, Abs));
+      return;
+    }
+
     if (Subtarget.hasStdExtZbb()) {
-      // Emit a special ABSW node that will be expanded to NEGW+MAX at isel.
+      // Emit a special node that will be expanded to NEGW+MAX at isel.
       // This allows us to remember that the result is sign extended. Expanding
       // to NEGW+MAX here requires a Freeze which breaks ComputeNumSignBits.
       SDValue Src = DAG.getNode(ISD::SIGN_EXTEND, DL, MVT::i64,
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoP.td b/llvm/lib/Target/RISCV/RISCVInstrInfoP.td
index cc085bb6c9fd7..4cbbba3aa68cb 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoP.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoP.td
@@ -1461,5 +1461,10 @@ let Predicates = [HasStdExtP, IsRV32] in {
 // Codegen patterns
 //===----------------------------------------------------------------------===//
 
+def riscv_absw : RVSDNode<"ABSW", SDTIntUnaryOp>;
+
 let Predicates = [HasStdExtP] in
 def : PatGpr<abs, ABS>;
+
+let Predicates = [HasStdExtP, IsRV64] in
+def : PatGpr<riscv_absw, ABSW>;
diff --git a/llvm/test/CodeGen/RISCV/rv64p.ll b/llvm/test/CodeGen/RISCV/rv64p.ll
index cb07f945a582a..f937f44f13320 100644
--- a/llvm/test/CodeGen/RISCV/rv64p.ll
+++ b/llvm/test/CodeGen/RISCV/rv64p.ll
@@ -297,8 +297,7 @@ declare i32 @llvm.abs.i32(i32, i1 immarg)
 define i32 @abs_i32(i32 %x) {
 ; CHECK-LABEL: abs_i32:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    sext.w a0, a0
-; CHECK-NEXT:    abs a0, a0
+; CHECK-NEXT:    absw a0, a0
 ; CHECK-NEXT:    ret
   %abs = tail call i32 @llvm.abs.i32(i32 %x, i1 true)
   ret i32 %abs
@@ -307,8 +306,7 @@ define i32 @abs_i32(i32 %x) {
 define signext i32 @abs_i32_sext(i32 signext %x) {
 ; CHECK-LABEL: abs_i32_sext:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    abs a0, a0
-; CHECK-NEXT:    sext.w a0, a0
+; CHECK-NEXT:    absw a0, a0
 ; CHECK-NEXT:    ret
   %abs = tail call i32 @llvm.abs.i32(i32 %x, i1 true)
   ret i32 %abs