From 2c6f6b4b2dbdd94a10a01124ac61724c412fe587 Mon Sep 17 00:00:00 2001
From: Quentin Carbonneaux <quentin.carbonneaux@yale.edu>
Date: Wed, 19 Aug 2015 14:56:33 -0400
Subject: [PATCH] add truncation operation

It would be nicer to have some kind of subtyping where a
l variable can be used in place of a w variable but it is
more complications than a truncation insutruction.

In some cases, it might be less efficient than the above
solution by requiring two registers instead of one.
(I.e when both the truncated variable and the long variable
live together.)

We have to see what are the usage patterns.
---
 lisc/emit.c  | 7 +++++++
 lisc/isel.c  | 4 ++++
 lisc/lisc.h  | 1 +
 lisc/parse.c | 1 +
 4 files changed, 13 insertions(+)

diff --git a/lisc/emit.c b/lisc/emit.c
index 1f2060b..e28832a 100644
--- a/lisc/emit.c
+++ b/lisc/emit.c
@@ -191,6 +191,13 @@ eins(Ins i, Fn *fn, FILE *f)
 			diag("emit: invalid extension");
 		eop(otoa[i.op], i.arg[0], i.to, fn, f);
 		break;
+	case OTrunc:
+		if (rtype(i.to) != RTmp || i.to.val < EAX
+		|| (rtype(i.arg[0]) == RTmp && i.arg[0].val >= EAX))
+			diag("emit: invalid truncation");
+		if (rtype(i.arg[0]) == RTmp)
+			i.arg[0] = TMP(RWORD(i.arg[0].val));
+		/* fall through */
 	case OCopy:
 		if (req(i.to, R))
 			break;
diff --git a/lisc/isel.c b/lisc/isel.c
index bace637..91df7dc 100644
--- a/lisc/isel.c
+++ b/lisc/isel.c
@@ -181,6 +181,9 @@ sel(Ins i, Fn *fn)
 	case OZext:
 		n = 0;
 		goto Emit;
+	case OTrunc:
+		n = 1;
+		goto Emit;
 	case OAdd:
 	case OSub:
 	case OMul:
@@ -285,6 +288,7 @@ flagi(Ins *i0, Ins *i)
 		case OCopy: /* flag-transparent */
 		case OSext:
 		case OZext:
+		case OTrunc:
 		case OStorel:
 		case OStorew:
 		case OStoreb:
diff --git a/lisc/lisc.h b/lisc/lisc.h
index d924701..b2f1c66 100644
--- a/lisc/lisc.h
+++ b/lisc/lisc.h
@@ -130,6 +130,7 @@ enum Op {
 	OAnd,
 	OSext,
 	OZext,
+	OTrunc,
 	OCmp,
 	OCmp1 = OCmp + NCmp-1,
 	OStorel,
diff --git a/lisc/parse.c b/lisc/parse.c
index 8ffdb74..9f8e7a6 100644
--- a/lisc/parse.c
+++ b/lisc/parse.c
@@ -20,6 +20,7 @@ OpDesc opdesc[NOp] = {
 	[OAnd]    = { "and",    2, 2 },
 	[OSext]   = { "sext",   1, 1 },
 	[OZext]   = { "zext",   1, 1 },
+	[OTrunc]  = { "trunc",  1, 1 },
 	[OStorel] = { "storel", 2, 0 },
 	[OStorew] = { "storew", 2, 0 },
 	[OStores] = { "stores", 2, 0 },