cranelift: Remove redundant branch and select instructions (#5097)

As discussed in the 2022/10/19 meeting, this PR removes many of the branch and select instructions that used iflags, in favor if using brz/brnz and select in their place. Additionally, it reworks selectif_spectre_guard to take an i8 input instead of an iflags input.

For reference, the removed instructions are: br_icmp, brif, brff, trueif, trueff, and selectif.

cranelift/codegen/src/machinst/isle.rs

@@ -8,8 +8,8 @@ use target_lexicon::Triple;
 
 pub use super::MachLabel;
 pub use crate::ir::{
-    condcodes, dynamic_to_fixed, ArgumentExtension, Constant, DynamicStackSlot, ExternalName,
-    FuncRef, GlobalValue, Immediate, SigRef, StackSlot,
+    condcodes, condcodes::CondCode, dynamic_to_fixed, ArgumentExtension, Constant,
+    DynamicStackSlot, ExternalName, FuncRef, GlobalValue, Immediate, SigRef, StackSlot,
 };
 pub use crate::isa::unwind::UnwindInst;
 pub use crate::machinst::{
@@ -570,6 +570,26 @@ macro_rules! isle_lower_prelude_methods {
         fn gen_move(&mut self, ty: Type, dst: WritableReg, src: Reg) -> MInst {
             MInst::gen_move(dst, src, ty)
         }
+
+        #[inline]
+        fn intcc_reverse(&mut self, cc: &IntCC) -> IntCC {
+            cc.reverse()
+        }
+
+        #[inline]
+        fn intcc_inverse(&mut self, cc: &IntCC) -> IntCC {
+            cc.inverse()
+        }
+
+        #[inline]
+        fn floatcc_reverse(&mut self, cc: &FloatCC) -> FloatCC {
+            cc.reverse()
+        }
+
+        #[inline]
+        fn floatcc_inverse(&mut self, cc: &FloatCC) -> FloatCC {
+            cc.inverse()
+        }
     };
 }