Add x64 isel support for the float constant 0

This is the only constant that doesn't require constant pool support, so
let's get it out of the way.

Author: nmraz

crates/codegen/src/target/x64/lower.rs

@@ -3,7 +3,7 @@ use core::mem;
 use alloc::vec::Vec;
 
 use ir::{
-    node::{FcmpKind, FunctionRef, IcmpKind, MemSize, NodeKind, Type},
+    node::{BitwiseF64, FcmpKind, FunctionRef, IcmpKind, MemSize, NodeKind, Type},
     valgraph::{DepValue, Node},
 };
 use smallvec::{SmallVec, smallvec};
@@ -191,6 +191,7 @@ impl MachineLower for X64Machine {
                 // `setcc` output register.
                 emit_setcc_sequence(ctx, output, |ctx| select_icmp(ctx, node, kind));
             }
+            &NodeKind::Fconst64(val) => select_fconst64(ctx, node, val)?,
             NodeKind::Fadd => emit_fpu_rr(ctx, node, SseFpuBinOp::Add),
             NodeKind::Fsub => emit_fpu_rr(ctx, node, SseFpuBinOp::Sub),
             NodeKind::Fmul => emit_fpu_rr(ctx, node, SseFpuBinOp::Mul),
@@ -401,6 +402,22 @@ fn select_icmp(ctx: &mut IselContext<'_, '_, X64Machine>, node: Node, kind: Icmp
     cond_code_for_icmp(kind)
 }
 
+fn select_fconst64(
+    ctx: &mut IselContext<'_, '_, X64Machine>,
+    node: Node,
+    val: BitwiseF64,
+) -> Result<(), MachineIselError> {
+    let [output] = ctx.node_outputs_exact(node);
+    let output = ctx.get_value_vreg(output);
+
+    if val.bits() == 0 {
+        ctx.emit_instr(X64Instr::SseMovRZ, &[DefOperand::any_reg(output)], &[]);
+        return Ok(());
+    }
+
+    Err(MachineIselError)
+}
+
 fn select_direct_fcmp(ctx: &mut IselContext<'_, '_, X64Machine>, node: Node, kind: FcmpKind) {
     let [output] = ctx.node_outputs_exact(node);
     let [op1, op2] = ctx.node_inputs_exact(node);

crates/filetests/cases/codegen/fconst.spdr

@@ -0,0 +1,14 @@
+# run: codegen
+
+func @zero64:f64() {
+    # check: function `zero64`:
+    # nextln: 000000: 55                              push rbp
+    # nextln: 000001: 48 89 e5                        mov rbp, rsp
+    # nextln: 000004: 0f 57 c0                        xorps xmm0, xmm0
+    # nextln: 000007: 5d                              pop rbp
+    # nextln: 000008: c3                              ret
+
+    %c:ctrl = entry
+    %0:f64 = fconst64 0x0
+    return %c, %0
+}

crates/filetests/cases/isel/fconst.spdr

@@ -0,0 +1,12 @@
+# run: isel
+
+func @zero64:f64() {
+    # check: function `zero64`:
+    # nextln:       block0[]:
+    # nextln: 0000:      %0:xmm(reg)[late] = SseMovRZ
+    # nextln: 0001:      Ret %0($$xmm0)[early]
+
+    %c:ctrl = entry
+    %0:f64 = fconst64 0x0
+    return %c, %0
+}