Merge pull request bytecodealliance#784 from julian-seward1/issue779

Only create copy_nop instructions for types for which an encoding exi…

cranelift/codegen/meta-python/isa/riscv/encodings.py

@@ -3,12 +3,13 @@
 """
 from __future__ import absolute_import
 from base import instructions as base
+from base import types
 from base.immediates import intcc
 from .defs import RV32, RV64
 from .recipes import OPIMM, OPIMM32, OP, OP32, LUI, BRANCH, JALR, JAL
 from .recipes import LOAD, STORE
 from .recipes import R, Rshamt, Ricmp, Ii, Iz, Iicmp, Iret, Icall, Icopy
-from .recipes import U, UJ, UJcall, SB, SBzero, GPsp, GPfi, Irmov
+from .recipes import U, UJ, UJcall, SB, SBzero, GPsp, GPfi, Irmov, stacknull
 from .settings import use_m
 from cdsl.ast import Var
 from base.legalize import narrow, expand
@@ -160,3 +161,9 @@
 RV64.enc(base.copy.b1, Icopy, OPIMM(0b000))
 RV32.enc(base.regmove.b1, Irmov, OPIMM(0b000))
 RV64.enc(base.regmove.b1, Irmov, OPIMM(0b000))
+
+# Stack-slot-to-the-same-stack-slot copy, which is guaranteed to turn
+# into a no-op.
+for ty in [types.i64, types.i32, types.i16, types.i8, types.f64, types.f32]:
+    RV64.enc(base.copy_nop.bind(ty), stacknull, 0)
+    RV32.enc(base.copy_nop.bind(ty), stacknull, 0)

cranelift/codegen/meta-python/isa/riscv/recipes.py

@@ -223,3 +223,8 @@ def LUI():
         'GPfi', Unary, base_size=4,
         ins=Stack(GPR), outs=GPR,
         emit='unimplemented!();')
+
+# Stack-slot-to-the-same-stack-slot copy, which is guaranteed to turn
+# into a no-op.
+stacknull = EncRecipe('stacknull', Unary, base_size=0,
+                      ins=Stack(GPR), outs=Stack(GPR), emit='')

cranelift/codegen/meta-python/isa/x86/encodings.py

@@ -342,11 +342,23 @@ def enc_i32_i64_ld_st(inst, w_bit, recipe, *args, **kwargs):
 X86_32.enc(base.copy_special, *r.copysp(0x89))
 
 # Stack-slot-to-the-same-stack-slot copy, which is guaranteed to turn
-# into a no-op.
-X86_64.enc(base.copy_nop.i64, r.stacknull, 0)
-X86_64.enc(base.copy_nop.i32, r.stacknull, 0)
-X86_64.enc(base.copy_nop.f64, r.stacknull, 0)
-X86_64.enc(base.copy_nop.f32, r.stacknull, 0)
+# into a no-op.  Ideally we could to make this encoding available for
+# all types, and write `base.copy_nop.any`, but it appears that the
+# controlling type variable must not polymorphic.  So we make do with
+# the following limited set, and guard the generating transformation in
+# regalloc/reload.rs accordingly.
+#
+# The same encoding is generated for both the 64- and 32-bit architectures.
+# Note that we can't use `enc_both` here, because that attempts to create a
+# variant with a REX prefix in the 64-bit-architecture case.  But since
+# there's no actual instruction for the REX prefix to modify the meaning of,
+# it will modify the meaning of whatever instruction happens to follow this
+# one, which is obviously wrong.  Note also that we can and indeed *must*
+# claim that there's a 64-bit encoding for the 32-bit arch case, even though
+# no such single instruction actually exists for the 32-bit arch case.
+for ty in [types.i64, types.i32, types.i16, types.i8, types.f64, types.f32]:
+    X86_64.enc(base.copy_nop.bind(ty), r.stacknull, 0)
+    X86_32.enc(base.copy_nop.bind(ty), r.stacknull, 0)
 
 # Adjust SP down by a dynamic value (or up, with a negative operand).
 X86_32.enc(base.adjust_sp_down.i32, *r.adjustsp(0x29))

cranelift/codegen/src/regalloc/reload.rs

@@ -222,18 +222,29 @@ impl<'a> Context<'a> {
         {
             let dst_vals = self.cur.func.dfg.inst_results(inst);
             if dst_vals.len() == 1 {
+                let dst_val = dst_vals[0];
                 let can_transform = match (
                     self.cur.func.locations[arg],
-                    self.cur.func.locations[dst_vals[0]],
+                    self.cur.func.locations[dst_val],
                 ) {
-                    (ValueLoc::Stack(src_slot), ValueLoc::Stack(dst_slot)) => src_slot == dst_slot,
+                    (ValueLoc::Stack(src_slot), ValueLoc::Stack(dst_slot)) => {
+                        src_slot == dst_slot && {
+                            let src_ty = self.cur.func.dfg.value_type(arg);
+                            let dst_ty = self.cur.func.dfg.value_type(dst_val);
+                            debug_assert!(src_ty == dst_ty);
+                            // This limits the transformation to copies of the
+                            // types: I64 I32 I16 I8 F64 and F32, since that's
+                            // the set of `copy_nop` encodings available.
+                            src_ty.is_int() || src_ty.is_float()
+                        }
+                    }
                     _ => false,
                 };
                 if can_transform {
                     // Convert the instruction into a `copy_nop`.
                     self.cur.func.dfg.replace(inst).copy_nop(arg);
                     let ok = self.cur.func.update_encoding(inst, self.cur.isa).is_ok();
-                    debug_assert!(ok);
+                    debug_assert!(ok, "copy_nop encoding missing for this type");
 
                     // And move on to the next insn.
                     self.reloads.clear();

cranelift/filetests/filetests/regalloc/reload-779.clif

@@ -0,0 +1,23 @@
+test compile
+target x86_64
+
+; Filed as https://github.com/CraneStation/cranelift/issues/779
+;
+; The copy_nop optimisation to reload (see Issue 773) was creating
+; copy_nop instructions for types for which there were no encoding.
+
+function u0:0(i64, i64, i64) system_v {
+    sig0 = () system_v
+    sig1 = (i16) system_v
+    fn1 = u0:94 sig0
+    fn2 = u0:95 sig1
+
+ebb0(v0: i64, v1: i64, v2: i64):
+    v3 = iconst.i16 0
+    jump ebb1(v3)
+
+ebb1(v4: i16):
+    call fn1()
+    call fn2(v4)
+    jump ebb1(v4)
+}