x64: use constant pool for u64 constants rather than movabs. (#4088)

* Allow emitting u64 constants into constant pool.

* Use constant pool for constants on x64 that do not fit in a simm32 and are needed as a RegMem or RegMemImm.

* Fix rip-relative addressing bug in pinsrd emission.

cranelift/codegen/src/isa/x64/lower/isle.rs

@@ -78,10 +78,11 @@ where
                 return imm.to_reg_mem_imm();
             }
 
-            // Generate constants fresh at each use to minimize long-range
+            // A load from the constant pool is better than a
+            // rematerialization into a register, because it reduces
             // register pressure.
-            let ty = self.value_type(val);
-            return RegMemImm::reg(generated_code::constructor_imm(self, ty, c).unwrap());
+            let vcode_constant = self.emit_u64_le_const(c);
+            return RegMemImm::mem(SyntheticAmode::ConstantOffset(vcode_constant));
         }
 
         if let InputSourceInst::UniqueUse(src_insn, 0) = inputs.inst {
@@ -99,10 +100,11 @@ where
         let inputs = self.lower_ctx.get_value_as_source_or_const(val);
 
         if let Some(c) = inputs.constant {
-            // Generate constants fresh at each use to minimize long-range
+            // A load from the constant pool is better than a
+            // rematerialization into a register, because it reduces
             // register pressure.
-            let ty = self.value_type(val);
-            return RegMem::reg(generated_code::constructor_imm(self, ty, c).unwrap());
+            let vcode_constant = self.emit_u64_le_const(c);
+            return RegMem::mem(SyntheticAmode::ConstantOffset(vcode_constant));
         }
 
         if let InputSourceInst::UniqueUse(src_insn, 0) = inputs.inst {

cranelift/codegen/src/isa/x64/lower/isle/generated_code.manifest

@@ -1,4 +1,4 @@
 src/clif.isle 443b34b797fc8ace
-src/prelude.isle 97c4b6eebbab9f05
-src/isa/x64/inst.isle a7f86254b89a7136
+src/prelude.isle e6c91b0115343ab9
+src/isa/x64/inst.isle 833710d359126637
 src/isa/x64/lower.isle 4c567e9157f84afb