[PATCH] D112089: consteval if does not form a discarded statement

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman created this revision.
aaron.ballman added reviewers: cor3ntin, erichkeane, rsmith.
aaron.ballman requested review of this revision.
Herald added a project: clang.

When we added support for `if consteval`, we accidentally formed a discarded statement evaluation context for the branch-not-taken. However, a discarded statement is a property of an `if constexpr` statement, not an `if consteval` statement (https://eel.is/c++draft/stmt.if#2.sentence-2). This turned out to cause issues when deducing the return type from a function with a consteval if statement -- we wouldn't consider the branch-not-taken when deducing the return type.

This fixes PR52206.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D112089

Files:
  clang/lib/Parse/ParseStmt.cpp
  clang/test/SemaCXX/cxx2b-consteval-if.cpp


Index: clang/test/SemaCXX/cxx2b-consteval-if.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/cxx2b-consteval-if.cpp
@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 -std=c++2b -verify %s
+
+namespace PR52206 {
+constexpr auto f() {
+  if consteval  { return 0;   }
+  if !consteval { return 0.0; } // expected-error {{'auto' in return type deduced as 'double' here but deduced as 'int' in earlier return statement}}
+}
+
+constexpr auto g() {
+  if !consteval { return 0;   }
+  if consteval  { return 0.0; } // expected-error {{'auto' in return type deduced as 'double' here but deduced as 'int' in earlier return statement}}
+}
+
+constexpr auto h() {
+  if consteval  { return 0; }
+  if !consteval { return 0; } // okay
+}
+
+constexpr auto i() {
+  if consteval {
+    if consteval { // expected-warning {{consteval if is always true in an immediate context}}
+	  return 1;
+	}
+	return 2;
+  } else {
+    return 1.0; // expected-error {{'auto' in return type deduced as 'double' here but deduced as 'int' in earlier return statement}}
+  }
+}
+
+void test() {
+  auto x1 = f();
+  constexpr auto y1 = f();
+
+  auto x2 = g();
+  constexpr auto y2 = g();
+
+  auto x3 = h();
+  constexpr auto y3 = h();
+
+  auto x4 = i();
+  constexpr auto y4 = i();
+}
+} // namespace PR52206
Index: clang/lib/Parse/ParseStmt.cpp
===================================================================
--- clang/lib/Parse/ParseStmt.cpp
+++ clang/lib/Parse/ParseStmt.cpp
@@ -1441,12 +1441,13 @@
   SourceLocation InnerStatementTrailingElseLoc;
   StmtResult ThenStmt;
   {
-    bool ShouldEnter =
-        (ConstexprCondition && !*ConstexprCondition) || IsConsteval;
+    bool ShouldEnter = ConstexprCondition && !*ConstexprCondition;
     Sema::ExpressionEvaluationContext Context =
         Sema::ExpressionEvaluationContext::DiscardedStatement;
-    if (NotLocation.isInvalid() && IsConsteval)
+    if (NotLocation.isInvalid() && IsConsteval) {
       Context = Sema::ExpressionEvaluationContext::ImmediateFunctionContext;
+      ShouldEnter = true;
+    }
 
     EnterExpressionEvaluationContext PotentiallyDiscarded(
         Actions, Context, nullptr,
@@ -1485,12 +1486,13 @@
                           Tok.is(tok::l_brace));
 
     MisleadingIndentationChecker MIChecker(*this, MSK_else, ElseLoc);
-    bool ShouldEnter =
-        (ConstexprCondition && *ConstexprCondition) || IsConsteval;
+    bool ShouldEnter = ConstexprCondition && *ConstexprCondition;
     Sema::ExpressionEvaluationContext Context =
         Sema::ExpressionEvaluationContext::DiscardedStatement;
-    if (NotLocation.isValid() && IsConsteval)
+    if (NotLocation.isValid() && IsConsteval) {
       Context = Sema::ExpressionEvaluationContext::ImmediateFunctionContext;
+      ShouldEnter = true;
+    }
 
     EnterExpressionEvaluationContext PotentiallyDiscarded(
         Actions, Context, nullptr,


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D112089.380751.patch
Type: text/x-patch
Size: 2919 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20211019/66d2d62f/attachment.bin>