[machinst x64]: allow addressing of constants

cranelift/codegen/src/isa/x64/inst/args.rs

@@ -3,6 +3,7 @@
 use super::regs::{self, show_ireg_sized};
 use super::EmitState;
 use crate::ir::condcodes::{FloatCC, IntCC};
+use crate::isa::x64::inst::Inst;
 use crate::machinst::*;
 use regalloc::{
     PrettyPrint, PrettyPrintSized, RealRegUniverse, Reg, RegClass, RegUsageCollector,
@@ -104,6 +105,9 @@ pub enum SyntheticAmode {
     /// A (virtual) offset to the "nominal SP" value, which will be recomputed as we push and pop
     /// within the function.
     NominalSPOffset { simm32: u32 },
+
+    /// A virtual offset to a constant that will be emitted in the constant section of the buffer.
+    ConstantOffset(VCodeConstant),
 }
 
 impl SyntheticAmode {
@@ -118,6 +122,7 @@ impl SyntheticAmode {
             SyntheticAmode::NominalSPOffset { .. } => {
                 // Nothing to do; the base is SP and isn't involved in regalloc.
             }
+            SyntheticAmode::ConstantOffset(_) => {}
         }
     }
 
@@ -127,10 +132,11 @@ impl SyntheticAmode {
             SyntheticAmode::NominalSPOffset { .. } => {
                 // Nothing to do.
             }
+            SyntheticAmode::ConstantOffset(_) => {}
         }
     }
 
-    pub(crate) fn finalize(&self, state: &mut EmitState) -> Amode {
+    pub(crate) fn finalize(&self, state: &mut EmitState, buffer: &MachBuffer<Inst>) -> Amode {
         match self {
             SyntheticAmode::Real(addr) => addr.clone(),
             SyntheticAmode::NominalSPOffset { simm32 } => {
@@ -142,6 +148,9 @@ impl SyntheticAmode {
                 );
                 Amode::imm_reg(off as u32, regs::rsp())
             }
+            SyntheticAmode::ConstantOffset(c) => {
+                Amode::rip_relative(buffer.get_label_for_constant(*c))
+            }
         }
     }
 }
@@ -159,6 +168,7 @@ impl PrettyPrint for SyntheticAmode {
             SyntheticAmode::NominalSPOffset { simm32 } => {
                 format!("rsp({} + virtual offset)", *simm32 as i32)
             }
+            SyntheticAmode::ConstantOffset(c) => format!("const({:?})", c),
         }
     }
 }