From 10016e0368c382363e168e45fac2cca4bc64e38f Mon Sep 17 00:00:00 2001
From: amp-59 <114923809+amp-59@users.noreply.github.com>
Date: Tue, 26 Dec 2023 23:14:48 +0000
Subject: [PATCH 1/2] Sema: fix crash compiling `@shlExact`

Updated `zirShl`, to compute `shl_exact` with `comptime_int` LHS operand
like `shl`, and added test case for `@shlExact` with `comptime_int` LHS
operand.
---
 src/Sema.zig                              | 22 +++++-----------------
 test/cases/shl_exact_comptime_int_lhs.zig |  6 ++++++
 2 files changed, 11 insertions(+), 17 deletions(-)
 create mode 100644 test/cases/shl_exact_comptime_int_lhs.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index a2ed81161b..c6cb1a8b2f 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -13247,32 +13247,20 @@ fn zirShl(
             }
             break :rs rhs_src;
         };
-
-        const val = switch (air_tag) {
+        const val = if (scalar_ty.zigTypeTag(mod) == .ComptimeInt)
+            try lhs_val.shl(rhs_val, lhs_ty, sema.arena, mod)
+        else switch (air_tag) {
             .shl_exact => val: {
                 const shifted = try lhs_val.shlWithOverflow(rhs_val, lhs_ty, sema.arena, mod);
-                if (scalar_ty.zigTypeTag(mod) == .ComptimeInt) {
-                    break :val shifted.wrapped_result;
-                }
                 if (shifted.overflow_bit.compareAllWithZero(.eq, mod)) {
                     break :val shifted.wrapped_result;
                 }
                 return sema.fail(block, src, "operation caused overflow", .{});
             },
-
-            .shl_sat => if (scalar_ty.zigTypeTag(mod) == .ComptimeInt)
-                try lhs_val.shl(rhs_val, lhs_ty, sema.arena, mod)
-            else
-                try lhs_val.shlSat(rhs_val, lhs_ty, sema.arena, mod),
-
-            .shl => if (scalar_ty.zigTypeTag(mod) == .ComptimeInt)
-                try lhs_val.shl(rhs_val, lhs_ty, sema.arena, mod)
-            else
-                try lhs_val.shlTrunc(rhs_val, lhs_ty, sema.arena, mod),
-
+            .shl_sat => try lhs_val.shlSat(rhs_val, lhs_ty, sema.arena, mod),
+            .shl => try lhs_val.shlTrunc(rhs_val, lhs_ty, sema.arena, mod),
             else => unreachable,
         };
-
         return Air.internedToRef(val.toIntern());
     } else lhs_src;
 
diff --git a/test/cases/shl_exact_comptime_int_lhs.zig b/test/cases/shl_exact_comptime_int_lhs.zig
new file mode 100644
index 0000000000..60860f5113
--- /dev/null
+++ b/test/cases/shl_exact_comptime_int_lhs.zig
@@ -0,0 +1,6 @@
+export fn entry() void {
+    if (@shlExact(1, 1) != 2) @compileError("should be 2");
+}
+
+// compile
+// output_mode=Obj

From 52ebba6bdf5662353ce11a701a3361cc0616c01c Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 4 Jan 2024 00:44:44 -0700
Subject: [PATCH 2/2] `@shlExact` fixups

* Add clarification in langref
* move test case to behavior tests
---
 doc/langref.html.in                       | 5 +++++
 test/behavior/math.zig                    | 2 ++
 test/cases/shl_exact_comptime_int_lhs.zig | 6 ------
 3 files changed, 7 insertions(+), 6 deletions(-)
 delete mode 100644 test/cases/shl_exact_comptime_int_lhs.zig

diff --git a/doc/langref.html.in b/doc/langref.html.in
index c07633273b..7b5d086f2d 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -9163,6 +9163,11 @@ test "@setRuntimeSafety" {
       The type of {#syntax#}shift_amt{#endsyntax#} is an unsigned integer with {#syntax#}log2(@typeInfo(T).Int.bits){#endsyntax#} bits.
               This is because {#syntax#}shift_amt >= @typeInfo(T).Int.bits{#endsyntax#} is undefined behavior.
       </p>
+      <p>
+      {#syntax#}comptime_int{#endsyntax#} is modeled as an integer with an infinite number of bits,
+      meaning that in such case, {#syntax#}@shlExact{#endsyntax#} always produces a result and
+      cannot produce a compile error.
+      </p>
       {#see_also|@shrExact|@shlWithOverflow#}
       {#header_close#}
 
diff --git a/test/behavior/math.zig b/test/behavior/math.zig
index 3d3c282854..4f9f7a673d 100644
--- a/test/behavior/math.zig
+++ b/test/behavior/math.zig
@@ -1314,6 +1314,8 @@ test "exact shift left" {
 
     try testShlExact(0b00110101);
     try comptime testShlExact(0b00110101);
+
+    if (@shlExact(1, 1) != 2) @compileError("should be 2");
 }
 fn testShlExact(x: u8) !void {
     const shifted = @shlExact(x, 2);
diff --git a/test/cases/shl_exact_comptime_int_lhs.zig b/test/cases/shl_exact_comptime_int_lhs.zig
deleted file mode 100644
index 60860f5113..0000000000
--- a/test/cases/shl_exact_comptime_int_lhs.zig
+++ /dev/null
@@ -1,6 +0,0 @@
-export fn entry() void {
-    if (@shlExact(1, 1) != 2) @compileError("should be 2");
-}
-
-// compile
-// output_mode=Obj