[llvm] [RISCV][FPEnv] Lowering of fpenv intrinsics (PR #141498)

[Serge Pavlov via llvm-commits]

https://github.com/spavloff created https://github.com/llvm/llvm-project/pull/141498

The change implements custom lowering of `get_fpenv`, `set_fpenv` and `reset_fpenv` for RISCV target.

>From 178b8bb2e8f438e4fedcc7b490b9e0dcdb85d99b Mon Sep 17 00:00:00 2001
From: Serge Pavlov <sepavloff at gmail.com>
Date: Mon, 26 May 2025 15:09:58 +0700
Subject: [PATCH] [RISCV][FPEnv] Lowering of fpenv intrinsics

The change implements custom lowering of `get_fpenv`, `set_fpenv` and
`reset_fpenv` for RISCV target.
---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp |  3 ++
 llvm/lib/Target/RISCV/RISCVInstrInfoF.td    | 11 +++++++
 llvm/test/CodeGen/RISCV/fpenv32.ll          | 33 +++++++++++++++++++++
 llvm/test/CodeGen/RISCV/fpenv64.ll          | 33 +++++++++++++++++++++
 4 files changed, 80 insertions(+)
 create mode 100644 llvm/test/CodeGen/RISCV/fpenv32.ll
 create mode 100644 llvm/test/CodeGen/RISCV/fpenv64.ll

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 0a849f49116ee..b4f8038041e78 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -649,6 +649,9 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
 
     setOperationAction(ISD::GET_ROUNDING, XLenVT, Custom);
     setOperationAction(ISD::SET_ROUNDING, MVT::Other, Custom);
+    setOperationAction(ISD::GET_FPENV, XLenVT, Legal);
+    setOperationAction(ISD::SET_FPENV, XLenVT, Legal);
+    setOperationAction(ISD::RESET_FPENV, MVT::Other, Legal);
   }
 
   setOperationAction({ISD::GlobalAddress, ISD::BlockAddress, ISD::ConstantPool,
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoF.td b/llvm/lib/Target/RISCV/RISCVInstrInfoF.td
index 84a75666e5f36..9edfe34e0b67b 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoF.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoF.td
@@ -736,6 +736,17 @@ def : LdPat<load, LW_INX, f32>;
 def : StPat<store, SW_INX, GPRF32, f32>;
 } // Predicates = [HasStdExtZfinx]
 
+/// Floating-point environment
+multiclass FPEnvironmentOps<Predicate HasFloatExt> {
+  let Predicates = [HasFloatExt] in {
+    def : Pat<(XLenVT (get_fpenv)), (CSRRS SysRegFCSR.Encoding, (XLenVT X0))>;
+    def : Pat<(set_fpenv (XLenVT GPR:$rs)), (CSRRW SysRegFCSR.Encoding, GPR:$rs)>;
+    def : Pat<(reset_fpenv), (CSRRW SysRegFCSR.Encoding, (XLenVT X0))>;
+  }
+}
+defm : FPEnvironmentOps<HasStdExtF>;
+defm : FPEnvironmentOps<HasStdExtZfinx>;
+
 let Predicates = [HasStdExtF, IsRV32] in {
 // Moves (no conversion)
 def : Pat<(bitconvert (i32 GPR:$rs1)), (FMV_W_X GPR:$rs1)>;
diff --git a/llvm/test/CodeGen/RISCV/fpenv32.ll b/llvm/test/CodeGen/RISCV/fpenv32.ll
new file mode 100644
index 0000000000000..4d4976d391f80
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/fpenv32.ll
@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=riscv32 -mattr=+f -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -mtriple=riscv32 -mattr=+zfinx -verify-machineinstrs < %s | FileCheck %s
+
+define i32 @func_get_fpenv() {
+; CHECK-LABEL: func_get_fpenv:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    frcsr a0
+; CHECK-NEXT:    ret
+entry:
+  %fpenv = call i32 @llvm.get.fpenv.i32()
+  ret i32 %fpenv
+}
+
+define void @func_set_fpenv(i32 %fpenv) {
+; CHECK-LABEL: func_set_fpenv:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    fscsr a0
+; CHECK-NEXT:    ret
+entry:
+  call void @llvm.set.fpenv.i32(i32 %fpenv)
+  ret void
+}
+
+define void @func_reset_fpenv() {
+; CHECK-LABEL: func_reset_fpenv:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    fscsr zero
+; CHECK-NEXT:    ret
+entry:
+  call void @llvm.reset.fpenv()
+  ret void
+}
diff --git a/llvm/test/CodeGen/RISCV/fpenv64.ll b/llvm/test/CodeGen/RISCV/fpenv64.ll
new file mode 100644
index 0000000000000..3a7a455c3eed1
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/fpenv64.ll
@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=riscv64 -mattr=+f -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -mtriple=riscv64 -mattr=+zfinx -verify-machineinstrs < %s | FileCheck %s
+
+define i64 @func_get_fpenv() {
+; CHECK-LABEL: func_get_fpenv:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    frcsr a0
+; CHECK-NEXT:    ret
+entry:
+  %fpenv = call i64 @llvm.get.fpenv.i64()
+  ret i64 %fpenv
+}
+
+define void @func_set_fpenv(i64 %fpenv) {
+; CHECK-LABEL: func_set_fpenv:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    fscsr a0
+; CHECK-NEXT:    ret
+entry:
+  call void @llvm.set.fpenv.i64(i64 %fpenv)
+  ret void
+}
+
+define void @func_reset_fpenv() {
+; CHECK-LABEL: func_reset_fpenv:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    fscsr zero
+; CHECK-NEXT:    ret
+entry:
+  call void @llvm.reset.fpenv()
+  ret void
+}