From a7eb13a1518d94c7ddbbfef4f19a7952bac21731 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <jolesen@mozilla.com>
Date: Fri, 8 Dec 2017 10:10:26 -0800
Subject: [PATCH] Expand unknown instructions to runtime library calls.

---
 .../filetests/isa/intel/legalize-libcall.cton | 15 +++++
 lib/cretonne/src/legalizer/libcall.rs         | 61 +++++++++++++++++++
 lib/cretonne/src/legalizer/mod.rs             |  9 +++
 3 files changed, 85 insertions(+)
 create mode 100644 cranelift/filetests/isa/intel/legalize-libcall.cton
 create mode 100644 lib/cretonne/src/legalizer/libcall.rs

diff --git a/cranelift/filetests/isa/intel/legalize-libcall.cton b/cranelift/filetests/isa/intel/legalize-libcall.cton
new file mode 100644
index 0000000000..2d249fd8df
--- /dev/null
+++ b/cranelift/filetests/isa/intel/legalize-libcall.cton
@@ -0,0 +1,15 @@
+test legalizer
+
+; Pre-SSE 4.1, we need to use runtime library calls for floating point rounding operations.
+set is_64bit
+isa intel
+
+function %floor(f32) -> f32 {
+ebb0(v0: f32):
+    v1 = floor v0
+    return v1
+}
+; check: function %floor(f32 [%xmm0]) -> f32 [%xmm0] native {
+; check: sig0 = (f32) -> f32 native
+; check: fn0 = sig0 %FloorF32
+; check: $v1 = call fn0($v0)
diff --git a/lib/cretonne/src/legalizer/libcall.rs b/lib/cretonne/src/legalizer/libcall.rs
new file mode 100644
index 0000000000..156a05b813
--- /dev/null
+++ b/lib/cretonne/src/legalizer/libcall.rs
@@ -0,0 +1,61 @@
+//! Expanding instructions as runtime library calls.
+
+use ir;
+use ir::InstBuilder;
+
+/// Try to expand `inst` as a library call, returning true is successful.
+pub fn expand_as_libcall(inst: ir::Inst, func: &mut ir::Function) -> bool {
+    // Does the opcode/ctrl_type combo even have a well-known runtime library name.
+    let libcall =
+        match ir::LibCall::for_inst(func.dfg[inst].opcode(), func.dfg.ctrl_typevar(inst)) {
+            Some(lc) => lc,
+            None => return false,
+        };
+
+    let funcref = find_funcref(libcall, func).unwrap_or_else(|| make_funcref(libcall, inst, func));
+
+    // Now we convert `inst` to a call. First save the arguments.
+    let mut args = Vec::new();
+    args.extend_from_slice(func.dfg.inst_args(inst));
+    // The replace builder will preserve the instruction result values.
+    func.dfg.replace(inst).call(funcref, &args);
+
+    // TODO: ask the ISA to legalize the signature.
+
+    true
+}
+
+/// Get the existing function reference for `libcall` in `func` if it exists.
+fn find_funcref(libcall: ir::LibCall, func: &ir::Function) -> Option<ir::FuncRef> {
+    // We're assuming that all libcall function decls are at the end.
+    // If we get this wrong, worst case we'll have duplicate libcall decls which is harmless.
+    for fref in func.dfg.ext_funcs.keys().rev() {
+        match func.dfg.ext_funcs[fref].name {
+            ir::ExternalName::LibCall(lc) => {
+                if lc == libcall {
+                    return Some(fref);
+                }
+            }
+            _ => break,
+        }
+    }
+    None
+}
+
+/// Create a funcref for `libcall` with a signature matching `inst`.
+fn make_funcref(libcall: ir::LibCall, inst: ir::Inst, func: &mut ir::Function) -> ir::FuncRef {
+    // Start with a native calling convention. We'll give the ISA a chance to change it.
+    let mut sig = ir::Signature::new(ir::CallConv::Native);
+    for &v in func.dfg.inst_args(inst) {
+        sig.params.push(ir::AbiParam::new(func.dfg.value_type(v)));
+    }
+    for &v in func.dfg.inst_results(inst) {
+        sig.returns.push(ir::AbiParam::new(func.dfg.value_type(v)));
+    }
+    let sigref = func.import_signature(sig);
+
+    func.import_function(ir::ExtFuncData {
+        name: ir::ExternalName::LibCall(libcall),
+        signature: sigref,
+    })
+}
diff --git a/lib/cretonne/src/legalizer/mod.rs b/lib/cretonne/src/legalizer/mod.rs
index 2781f5fe84..8849e215e8 100644
--- a/lib/cretonne/src/legalizer/mod.rs
+++ b/lib/cretonne/src/legalizer/mod.rs
@@ -23,10 +23,12 @@ use timing;
 mod boundary;
 mod globalvar;
 mod heap;
+mod libcall;
 mod split;
 
 use self::globalvar::expand_global_addr;
 use self::heap::expand_heap_addr;
+use self::libcall::expand_as_libcall;
 
 /// Legalize `func` for `isa`.
 ///
@@ -88,6 +90,13 @@ pub fn legalize_function(func: &mut ir::Function, cfg: &mut ControlFlowGraph, is
                         pos.set_position(prev_pos);
                         continue;
                     }
+
+                    // We don't have any pattern expansion for this instruction either.
+                    // Try converting it to a library call as a last resort.
+                    if expand_as_libcall(inst, pos.func) {
+                        pos.set_position(prev_pos);
+                        continue;
+                    }
                 }
             }