From ca332f57f712c3b4570ca42bc503824022115142 Mon Sep 17 00:00:00 2001
From: Cody Tapscott <topolarity@tapscott.me>
Date: Sun, 30 Oct 2022 12:25:49 -0700
Subject: [PATCH] stage2: Make `x and false`/`x or true` comptime-known

Same as preceding change, but for stage2.
---
 src/Sema.zig           | 23 +++++++++++++------
 test/behavior/eval.zig | 50 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 7 deletions(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index a73c1eedcb..34b22f5073 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -15932,12 +15932,10 @@ fn zirBoolBr(
     const gpa = sema.gpa;
 
     if (try sema.resolveDefinedValue(parent_block, lhs_src, lhs)) |lhs_val| {
-        if (lhs_val.toBool() == is_bool_or) {
-            if (is_bool_or) {
-                return Air.Inst.Ref.bool_true;
-            } else {
-                return Air.Inst.Ref.bool_false;
-            }
+        if (is_bool_or and lhs_val.toBool()) {
+            return Air.Inst.Ref.bool_true;
+        } else if (!is_bool_or and !lhs_val.toBool()) {
+            return Air.Inst.Ref.bool_false;
         }
         // comptime-known left-hand side. No need for a block here; the result
         // is simply the rhs expression. Here we rely on there only being 1
@@ -15977,7 +15975,18 @@ fn zirBoolBr(
         _ = try rhs_block.addBr(block_inst, rhs_result);
     }
 
-    return finishCondBr(sema, parent_block, &child_block, &then_block, &else_block, lhs, block_inst);
+    const result = finishCondBr(sema, parent_block, &child_block, &then_block, &else_block, lhs, block_inst);
+    if (!sema.typeOf(rhs_result).isNoReturn()) {
+        if (try sema.resolveDefinedValue(rhs_block, sema.src, rhs_result)) |rhs_val| {
+            if (is_bool_or and rhs_val.toBool()) {
+                return Air.Inst.Ref.bool_true;
+            } else if (!is_bool_or and !rhs_val.toBool()) {
+                return Air.Inst.Ref.bool_false;
+            }
+        }
+    }
+
+    return result;
 }
 
 fn finishCondBr(
diff --git a/test/behavior/eval.zig b/test/behavior/eval.zig
index 7e46633172..617cc6dfd4 100644
--- a/test/behavior/eval.zig
+++ b/test/behavior/eval.zig
@@ -1438,3 +1438,53 @@ test "continue nested inline for loop in named block expr" {
     }
     try expect(a == 2);
 }
+
+test "x and false is comptime-known false" {
+    const T = struct {
+        var x: u32 = 0;
+
+        fn foo() bool {
+            x += 1; // Observable side-effect
+            return true;
+        }
+    };
+
+    if (T.foo() and T.foo() and false and T.foo()) {
+        @compileError("Condition should be comptime-known false");
+    }
+    try expect(T.x == 2);
+
+    T.x = 0;
+    if (T.foo() and T.foo() and b: {
+        _ = T.foo();
+        break :b false;
+    } and T.foo()) {
+        @compileError("Condition should be comptime-known false");
+    }
+    try expect(T.x == 3);
+}
+
+test "x or true is comptime-known true" {
+    const T = struct {
+        var x: u32 = 0;
+
+        fn foo() bool {
+            x += 1; // Observable side-effect
+            return false;
+        }
+    };
+
+    if (!(T.foo() or T.foo() or true or T.foo())) {
+        @compileError("Condition should be comptime-known false");
+    }
+    try expect(T.x == 2);
+
+    T.x = 0;
+    if (!(T.foo() or T.foo() or b: {
+        _ = T.foo();
+        break :b true;
+    } or T.foo())) {
+        @compileError("Condition should be comptime-known false");
+    }
+    try expect(T.x == 3);
+}