nak: add support for findmsb,findlsb

These all map into OpBFind, which is sourced from PTX and NV50.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24998>

src/nouveau/compiler/nak_encode_sm75.rs

@@ -1504,6 +1504,21 @@ impl SM75Instr {
         );
     }
 
+    fn encode_bfind(&mut self, op: &OpBFind) {
+        self.encode_alu(
+            0x100,
+            Some(op.dst),
+            ALUSrc::None,
+            ALUSrc::from_src(&op.src),
+            ALUSrc::None,
+        );
+        self.set_pred_dst(81..84, Dst::None);
+        self.set_field(74..75, op.return_shift_amount as u8);
+        self.set_field(73..74, op.signed as u8);
+        let not_mod = matches!(op.src.src_mod, SrcMod::BNot);
+        self.set_field(63..64, not_mod)
+    }
+
     pub fn encode(
         instr: &Instr,
         sm: u8,
@@ -1564,6 +1579,7 @@ impl SM75Instr {
             Op::S2R(op) => si.encode_s2r(&op),
             Op::PopC(op) => si.encode_popc(&op),
             Op::Brev(op) => si.encode_brev(&op),
+            Op::BFind(op) => si.encode_bfind(&op),
             _ => panic!("Unhandled instruction"),
         }
 

src/nouveau/compiler/nak_from_nir.rs

@@ -224,6 +224,21 @@ impl<'a> ShaderFromNir<'a> {
                 });
                 dst
             }
+            nir_op_find_lsb => {
+                let tmp = b.alloc_ssa(RegFile::GPR, 1);
+                b.push_op(OpBrev {
+                    dst: tmp.into(),
+                    src: srcs[0],
+                });
+                let dst = b.alloc_ssa(RegFile::GPR, 1);
+                b.push_op(OpBFind {
+                    dst: dst.into(),
+                    src: tmp.into(),
+                    signed: alu.op == nir_op_ifind_msb,
+                    return_shift_amount: true,
+                });
+                dst
+            }
             nir_op_f2i32 | nir_op_f2u32 => {
                 let src_bits = usize::from(alu.get_src(0).bit_size());
                 let dst_bits = alu.def.bit_size();
@@ -450,6 +465,16 @@ impl<'a> ShaderFromNir<'a> {
                     b.isetp(IntCmpType::I32, IntCmpOp::Eq, srcs[0], srcs[1])
                 }
             }
+            nir_op_ifind_msb | nir_op_ufind_msb => {
+                let dst = b.alloc_ssa(RegFile::GPR, 1);
+                b.push_op(OpBFind {
+                    dst: dst.into(),
+                    src: srcs[0],
+                    signed: alu.op == nir_op_ifind_msb,
+                    return_shift_amount: false,
+                });
+                dst
+            }
             nir_op_ige => {
                 b.isetp(IntCmpType::I32, IntCmpOp::Ge, srcs[0], srcs[1])
             }

src/nouveau/compiler/nak_ir.rs

@@ -3165,6 +3165,28 @@ impl fmt::Display for OpBrev {
     }
 }
 
+#[repr(C)]
+#[derive(SrcsAsSlice, DstsAsSlice)]
+pub struct OpBFind {
+    pub dst: Dst,
+
+    #[src_type(ALU)]
+    pub src: Src,
+
+    pub signed: bool,
+    pub return_shift_amount: bool,
+}
+
+impl fmt::Display for OpBFind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "BFIND")?;
+        if self.return_shift_amount {
+            write!(f, ".SAMT")?;
+        }
+        write!(f, " {} {}", self.dst, self.src)
+    }
+}
+
 #[derive(Display, DstsAsSlice, SrcsAsSlice, FromVariants)]
 pub enum Op {
     FAdd(OpFAdd),
@@ -3221,6 +3243,7 @@ pub enum Op {
     FSOut(OpFSOut),
     PopC(OpPopC),
     Brev(OpBrev),
+    BFind(OpBFind),
 }
 
 #[derive(Clone, Copy, Eq, Hash, PartialEq)]
@@ -3537,7 +3560,7 @@ impl Instr {
             | Op::FSOut(_) => {
                 panic!("Not a hardware opcode")
             }
-            Op::PopC(_) | Op::Brev(_) => Some(15),
+            Op::PopC(_) | Op::Brev(_) | Op::BFind(_) => Some(15),
         }
     }
 }

src/nouveau/compiler/nak_legalize.rs

@@ -188,7 +188,8 @@ impl<'a> LegalizeInstr<'a> {
             | Op::Mov(_)
             | Op::FRnd(_)
             | Op::PopC(_)
-            | Op::Brev(_) => (),
+            | Op::Brev(_)
+            | Op::BFind(_) => (),
             Op::Sel(op) => {
                 let [ref mut src0, ref mut src1] = op.srcs;
                 if !src_is_reg(src0) && src_is_reg(src1) {