Fix problem with let-bindings in pattern guards

Monomorphisation sometimes produces pattern guard with let-bindings, e.g.

| ... if (let regsize = size_itself(regsize) in eq(regsize, 32)) -> ...

Previously, the rewriting pass for let-bindings (and pattern guards) pulled
these out of the guard condition and into the same scope as the case
expression, which potentially clashed with let-bindings for the same variables
in that case expression.  The rewriter now leaves let-bindings in place within
pure if-conditions, solving this problem.

1 files changed, 9 insertions, 7 deletions

diff --git a/src/rewrites.ml b/src/rewrites.ml
index 950013ff..7e852092 100644
--- a/src/rewrites.ml
+++ b/src/rewrites.ml
@@ -2313,13 +2313,15 @@ let rewrite_defs_letbind_effects  =
        n_exp_nameL exps (fun exps ->
        k (rewrap (E_tuple exps)))
     | E_if (exp1,exp2,exp3) ->
-       n_exp_name exp1 (fun exp1 ->
-       let (E_aux (_,annot2)) = exp2 in
-       let (E_aux (_,annot3)) = exp3 in
-       let newreturn = effectful exp2 || effectful exp3 in
-       let exp2 = n_exp_term newreturn exp2 in
-       let exp3 = n_exp_term newreturn exp3 in
-       k (rewrap (E_if (exp1,exp2,exp3))))
+       let e_if exp1 =
+         let (E_aux (_,annot2)) = exp2 in
+         let (E_aux (_,annot3)) = exp3 in
+         let newreturn = effectful exp2 || effectful exp3 in
+         let exp2 = n_exp_term newreturn exp2 in
+         let exp3 = n_exp_term newreturn exp3 in
+         k (rewrap (E_if (exp1,exp2,exp3)))
+       in
+       if value exp1 then e_if (n_exp_term false exp1) else n_exp_name exp1 e_if
     | E_for (id,start,stop,by,dir,body) ->
        n_exp_name start (fun start -> 
        n_exp_name stop (fun stop ->