Comment the new rule for emit_cmp

bytecodealliance · Aug 8, 2022 · bb4bbfb · bb4bbfb
1 parent d909d2c
commit bb4bbfb
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/cranelift/codegen/src/isa/x64/inst.isle b/cranelift/codegen/src/isa/x64/inst.isle
@@ -3181,6 +3181,9 @@
       (let ((size OperandSize (raw_operand_size_of_type ty)))
         (icmp_cond_result (x64_cmp size b a) cc)))
 
+;; As a special case, reverse the arguments to the comparison when the LHS is a
+;; constant. This ensures that we avoid moving the constant into a register when
+;; performing the comparison.
 (rule 1 (emit_cmp cc (and (simm32_from_value a) (value_type ty)) b)
       (let ((size OperandSize (raw_operand_size_of_type ty)))
         (icmp_cond_result (x64_cmp size a b) (intcc_reverse cc))))