radeonsi: clean up ffma handling

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6596>

src/amd/llvm/ac_nir_to_llvm.c

@@ -853,10 +853,10 @@ static void visit_alu(struct ac_nir_context *ctx, const nir_alu_instr *instr)
       }
       break;
    case nir_op_ffma:
-      /* FMA is better on GFX10, because it has FMA units instead of MUL-ADD units. */
-      result =
-         emit_intrin_3f_param(&ctx->ac, ctx->ac.chip_class >= GFX10 ? "llvm.fma" : "llvm.fmuladd",
-                              ac_to_float_type(&ctx->ac, def_type), src[0], src[1], src[2]);
+      /* FMA is slow on gfx6-8, so it shouldn't be used. */
+      assert(ctx->ac.chip_class >= GFX9);
+      result = emit_intrin_3f_param(&ctx->ac, "llvm.fma", ac_to_float_type(&ctx->ac, def_type),
+                                    src[0], src[1], src[2]);
       break;
    case nir_op_ldexp:
       src[0] = ac_to_float(&ctx->ac, src[0]);