From 0c30799d4039c30f95eee29e2c2f8f604e8b9880 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Sun, 30 Jan 2022 15:23:40 -0700
Subject: Sema: fix comptime shl for fixed-width integers

---
 src/Sema.zig  |  8 +++++++-
 src/value.zig | 13 +++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/Sema.zig b/src/Sema.zig
index b3be9cadc8..7180a0959c 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -7474,11 +7474,17 @@ fn zirShl(
         }
         const val = switch (air_tag) {
             .shl_exact => return sema.fail(block, lhs_src, "TODO implement Sema for comptime shl_exact", .{}),
+
             .shl_sat => if (lhs_ty.zigTypeTag() == .ComptimeInt)
                 try lhs_val.shl(rhs_val, sema.arena)
             else
                 try lhs_val.shlSat(rhs_val, lhs_ty, sema.arena, sema.mod.getTarget()),
-            .shl => try lhs_val.shl(rhs_val, sema.arena),
+
+            .shl => if (lhs_ty.zigTypeTag() == .ComptimeInt)
+                try lhs_val.shl(rhs_val, sema.arena)
+            else
+                try lhs_val.shlTrunc(rhs_val, lhs_ty, sema.arena, sema.mod.getTarget()),
+
             else => unreachable,
         };
 
diff --git a/src/value.zig b/src/value.zig
index df1531533b..6c2403e13b 100644
--- a/src/value.zig
+++ b/src/value.zig
@@ -2883,6 +2883,19 @@ pub const Value = extern union {
         return fromBigInt(arena, result_bigint.toConst());
     }
 
+    pub fn shlTrunc(
+        lhs: Value,
+        rhs: Value,
+        ty: Type,
+        arena: Allocator,
+        target: Target,
+    ) !Value {
+        const shifted = try lhs.shl(rhs, arena);
+        const int_info = ty.intInfo(target);
+        const truncated = try shifted.intTrunc(arena, int_info.signedness, int_info.bits);
+        return truncated;
+    }
+
     pub fn shr(lhs: Value, rhs: Value, allocator: Allocator) !Value {
         // TODO is this a performance issue? maybe we should try the operation without
         // resorting to BigInt first.
-- 
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