[clang][bytecode] Fail on reads from constexpr-unknown pointers

[tbaederr]

If they aren't const.

Fixes #164985

[llvmbot]

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

Changes

If they aren't const.

Fixes #164985

---

Full diff: https://github.com/llvm/llvm-project/pull/164996.diff

2 Files Affected:

• (modified) clang/lib/AST/ByteCode/Interp.cpp (+2)
• (added) clang/test/AST/ByteCode/codegen-cxx20.cpp (+15)

diff --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index a72282caf5e73..5d89f32d6bdc2 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/clang/lib/AST/ByteCode/Interp.cpp
@@ -832,6 +832,8 @@ bool CheckLoad(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
     return false;
   if (!CheckVolatile(S, OpPC, Ptr, AK))
     return false;
+  if (!Ptr.isConst() && !S.inConstantContext() && isConstexprUnknown(Ptr))
+    return false;
   return true;
 }
 
diff --git a/clang/test/AST/ByteCode/codegen-cxx20.cpp b/clang/test/AST/ByteCode/codegen-cxx20.cpp
new file mode 100644
index 0000000000000..c1ef629da1e88
--- /dev/null
+++ b/clang/test/AST/ByteCode/codegen-cxx20.cpp
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -triple x86_64-linux -emit-llvm -o - %s -fcxx-exceptions                                         | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-linux -emit-llvm -o - %s -fcxx-exceptions -fexperimental-new-constant-interpreter | FileCheck %s
+
+
+/// The read from a used to succeed, causing the entire if statement to vanish.
+extern void e();
+int somefunc() {
+  auto foo = [a = false]() mutable {
+    if (a)
+      e();
+  };
+  foo();
+}
+
+// CHECK: call void @_Z1ev()

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-aarch64-quick running on linaro-clang-aarch64-quick while building clang at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/24562

Here is the relevant piece of the build log for the reference

Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'lit :: max-time.py' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 5
env -u FILECHECK_OPTS "/usr/bin/python3.10" /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 --order=lexical Inputs/max-time --max-time=5 2>&1  |  FileCheck /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/max-time.py
# executed command: env -u FILECHECK_OPTS /usr/bin/python3.10 /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 --order=lexical Inputs/max-time --max-time=5
# executed command: FileCheck /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/max-time.py
# .---command stderr------------
# | /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/max-time.py:8:10: error: CHECK: expected string not found in input
# | # CHECK: Skipped: 1
# |          ^
# | <stdin>:2:51: note: scanning from here
# | warning: reached timeout, skipping remaining tests
# |                                                   ^
# | <stdin>:7:2: note: possible intended match here
# |  Skipped: 2 (100.00%)
# |  ^
# | 
# | Input file: <stdin>
# | Check file: /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/max-time.py
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |            1: -- Testing: 2 tests, 1 workers -- 
# |            2: warning: reached timeout, skipping remaining tests 
# | check:8'0                                                       X error: no match found
# |            3:  
# | check:8'0     ~
# |            4: Testing Time: 5.17s 
# | check:8'0     ~~~~~~~~~~~~~~~~~~~~
# |            5:  
# | check:8'0     ~
# |            6: Total Discovered Tests: 2 
# | check:8'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~
# |            7:  Skipped: 2 (100.00%) 
# | check:8'0     ~~~~~~~~~~~~~~~~~~~~~~
# | check:8'1      ?                     possible intended match
# | >>>>>>
# `-----------------------------
# error: command failed with exit status: 1

--

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