cranelift: Implement scalar FMA on x86 (#4460)

x86 does not have dedicated instructions for scalar FMA, lower
to a libcall which seems to be what llvm does.

cranelift/codegen/src/isa/aarch64/lower.rs

@@ -1551,7 +1551,7 @@ impl LowerBackend for AArch64Backend {
     type MInst = Inst;
 
     fn lower<C: LowerCtx<I = Inst>>(&self, ctx: &mut C, ir_inst: IRInst) -> CodegenResult<()> {
-        lower_inst::lower_insn_to_regs(ctx, ir_inst, &self.flags, &self.isa_flags)
+        lower_inst::lower_insn_to_regs(ctx, ir_inst, &self.triple, &self.flags, &self.isa_flags)
     }
 
     fn lower_branch_group<C: LowerCtx<I = Inst>>(

cranelift/codegen/src/isa/aarch64/lower/isle.rs

@@ -30,6 +30,7 @@ use regalloc2::PReg;
 use std::boxed::Box;
 use std::convert::TryFrom;
 use std::vec::Vec;
+use target_lexicon::Triple;
 
 type BoxCallInfo = Box<CallInfo>;
 type BoxCallIndInfo = Box<CallIndInfo>;
@@ -40,6 +41,7 @@ type BoxExternalName = Box<ExternalName>;
 /// The main entry point for lowering with ISLE.
 pub(crate) fn lower<C>(
     lower_ctx: &mut C,
+    triple: &Triple,
     flags: &Flags,
     isa_flags: &IsaFlags,
     outputs: &[InsnOutput],
@@ -48,9 +50,15 @@ pub(crate) fn lower<C>(
 where
     C: LowerCtx<I = MInst>,
 {
-    lower_common(lower_ctx, flags, isa_flags, outputs, inst, |cx, insn| {
-        generated_code::constructor_lower(cx, insn)
-    })
+    lower_common(
+        lower_ctx,
+        triple,
+        flags,
+        isa_flags,
+        outputs,
+        inst,
+        |cx, insn| generated_code::constructor_lower(cx, insn),
+    )
 }
 
 pub struct ExtendedValue {

cranelift/codegen/src/isa/aarch64/lower_inst.rs

@@ -16,11 +16,13 @@ use crate::{CodegenError, CodegenResult};
 use alloc::boxed::Box;
 use alloc::vec::Vec;
 use core::convert::TryFrom;
+use target_lexicon::Triple;
 
 /// Actually codegen an instruction's results into registers.
 pub(crate) fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
     ctx: &mut C,
     insn: IRInst,
+    triple: &Triple,
     flags: &Flags,
     isa_flags: &aarch64_settings::Flags,
 ) -> CodegenResult<()> {
@@ -33,7 +35,7 @@ pub(crate) fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
         None
     };
 
-    if let Ok(()) = super::lower::isle::lower(ctx, flags, isa_flags, &outputs, insn) {
+    if let Ok(()) = super::lower::isle::lower(ctx, triple, flags, isa_flags, &outputs, insn) {
         return Ok(());
     }