[clang] Convert second arg of __builtin_assume_aligned to ConstantExpr #161314

tbaederr · 2025-09-30T04:53:19Z

Since the second argument must be a constant integer, we can as well convert it to a ConstantExpr in Sema.

Fixes #161272

llvmbot · 2025-09-30T04:53:52Z

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

Changes

Since the second argument must be a constant integer, we can as well convert it to a ConstantExpr in Sema.

Fixes #161272

Full diff: https://github.com/llvm/llvm-project/pull/161314.diff

2 Files Affected:

(modified) clang/lib/Sema/SemaChecking.cpp (+3)
(modified) clang/test/SemaCXX/builtin-assume-aligned.cpp (+6)

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 39c3aa2243338..7b37e0b8d5430 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -5954,6 +5954,9 @@ bool Sema::BuiltinAssumeAligned(CallExpr *TheCall) {
     if (Result > Sema::MaximumAlignment)
       Diag(TheCall->getBeginLoc(), diag::warn_assume_aligned_too_great)
           << SecondArg->getSourceRange() << Sema::MaximumAlignment;
+
+    TheCall->setArg(1,
+                    ConstantExpr::Create(Context, SecondArg, APValue(Result)));
   }
 
   if (NumArgs > 2) {
diff --git a/clang/test/SemaCXX/builtin-assume-aligned.cpp b/clang/test/SemaCXX/builtin-assume-aligned.cpp
index 48bd8414fc50a..afc11cc694705 100644
--- a/clang/test/SemaCXX/builtin-assume-aligned.cpp
+++ b/clang/test/SemaCXX/builtin-assume-aligned.cpp
@@ -47,3 +47,9 @@ constexpr void *s1 = __builtin_assume_aligned(x, 32);
 constexpr void *s2 = __builtin_assume_aligned(x, 32, 5);
 constexpr void *s3 = __builtin_assume_aligned(x, 32, -1);
 
+
+constexpr int add(int a, int b) {
+  return a+b;
+}
+constexpr void *c1 = __builtin_assume_aligned(p, add(1,1));
+constexpr void *c2 = __builtin_assume_aligned(p, add(2,1)); // expected-error {{not a power of 2}}

cor3ntin · 2025-09-30T06:27:44Z

Can you add a changelog entry? Thanks

alanzhao1 · 2025-10-01T22:58:49Z

Heads up - this PR is causing us to hit the following assertion in https://github.com/google/highway. I'm currently running cvise to get a minimal reproducer.

bin/clang -o /dev/null -O3 ~/Downloads/out.ii -std=gnu++20
clang-21: /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGValue.h:274: void clang::CodeGen::LValue::initializeSimpleLValue(Address, QualType, LValueBaseInfo, TBAAAccessInfo, ASTContext &): Assertion `Addr.getBasePointer()->getType()->isPointerTy()' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: /usr/local/google/home/ayzhao/src/llvm-project/build-debug/bin/clang-21 -cc1 -triple x86_64-unknown-linux-gnu -O3 -emit-obj -dumpdir /dev/null- -disable-free -clear-ast-before-backend -main-file-name out.ii -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -fdebug-compilation-dir=/usr/local/google/home/ayzhao/src/llvm-project/build-debug -fcoverage-compilation-dir=/usr/local/google/home/ayzhao/src/llvm-project/build-debug -resource-dir /usr/local/google/home/ayzhao/src/llvm-project/build-debug/lib/clang/22 -std=gnu++20 -fdeprecated-macro -ferror-limit 19 -fmessage-length=160 -fgnuc-version=4.2.1 -fno-implicit-modules -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -fcolor-diagnostics -vectorize-loops -vectorize-slp -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/out-66e06c.o -x c++-cpp-output /usr/local/google/home/ayzhao/Downloads/out.ii
1.      <eof> parser at end of file
2.      third_party/highway/hwy/aligned_allocator.cc:27:11: LLVM IR generation of declaration 'hwy'
3.      third_party/highway/hwy/aligned_allocator.cc:69:21: Generating code for declaration 'hwy::AllocateAlignedBytes'
 #0 0x000056406ce4bbfd llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /usr/local/google/home/ayzhao/src/llvm-project/llvm/lib/Support/Unix/Signals.inc:834:11
 #1 0x000056406ce4c12b PrintStackTraceSignalHandler(void*) /usr/local/google/home/ayzhao/src/llvm-project/llvm/lib/Support/Unix/Signals.inc:917:1
 #2 0x000056406ce4a03f llvm::sys::RunSignalHandlers() /usr/local/google/home/ayzhao/src/llvm-project/llvm/lib/Support/Signals.cpp:104:5
 #3 0x000056406ce4c7c9 SignalHandler(int, siginfo_t*, void*) /usr/local/google/home/ayzhao/src/llvm-project/llvm/lib/Support/Unix/Signals.inc:426:38
 #4 0x00007f81e2649df0 (/lib/x86_64-linux-gnu/libc.so.6+0x3fdf0)
 #5 0x00007f81e269e95c __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #6 0x00007f81e2649cc2 raise ./signal/../sysdeps/posix/raise.c:27:6
 #7 0x00007f81e26324ac abort ./stdlib/abort.c:81:3
 #8 0x00007f81e2632420 __assert_perror_fail ./assert/assert-perr.c:31:1
 #9 0x000056406d3b969a clang::CodeGen::LValue::initializeSimpleLValue(clang::CodeGen::Address, clang::QualType, clang::CodeGen::LValueBaseInfo, clang::CodeGen::TBAAAccessInfo, clang::ASTContext&) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGValue.h:275:3
#10 0x000056406d3ab630 clang::CodeGen::LValue::MakeAddr(clang::CodeGen::Address, clang::QualType, clang::ASTContext&, clang::CodeGen::LValueBaseInfo, clang::CodeGen::TBAAAccessInfo) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGValue.h:436:7
#11 0x000056406d47784e clang::CodeGen::CodeGenFunction::EmitLoadOfScalar(clang::CodeGen::Address, bool, clang::QualType, clang::SourceLocation, clang::CodeGen::LValueBaseInfo, clang::CodeGen::TBAAAccessInfo, bool) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGExpr.cpp:2129:7
#12 0x000056406d3aad30 clang::CodeGen::CodeGenFunction::EmitLoadOfScalar(clang::CodeGen::Address, bool, clang::QualType, clang::SourceLocation, clang::CodeGen::AlignmentSource, bool) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenFunction.h:4310:5
#13 0x000056406d6bee94 (anonymous namespace)::ScalarExprEmitter::VisitConstantExpr(clang::ConstantExpr*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGExprScalar.cpp:469:9
#14 0x000056406d6b6979 clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(clang::Stmt*) /usr/local/google/home/ayzhao/src/llvm-project/build-debug/tools/clang/include/clang/AST/StmtNodes.inc:404:1
#15 0x000056406d6ac425 (anonymous namespace)::ScalarExprEmitter::Visit(clang::Expr*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGExprScalar.cpp:452:52
#16 0x000056406d6ac262 clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGExprScalar.cpp:5882:3
#17 0x000056406dafbc39 clang::CodeGen::CodeGenFunction::EmitBuiltinExpr(clang::GlobalDecl, unsigned int, clang::CallExpr const*, clang::CodeGen::ReturnValueSlot) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGBuiltin.cpp:3542:12
#18 0x000056406d48648c clang::CodeGen::CodeGenFunction::EmitCallExpr(clang::CallExpr const*, clang::CodeGen::ReturnValueSlot, llvm::CallBase**) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGExpr.cpp:5968:12
#19 0x000056406d6c0061 (anonymous namespace)::ScalarExprEmitter::VisitCallExpr(clang::CallExpr const*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGExprScalar.cpp:631:36
#20 0x000056406d6b6be1 clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(clang::Stmt*) /usr/local/google/home/ayzhao/src/llvm-project/build-debug/tools/clang/include/clang/AST/StmtNodes.inc:608:1
#21 0x000056406d6ac425 (anonymous namespace)::ScalarExprEmitter::Visit(clang::Expr*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGExprScalar.cpp:452:52
#22 0x000056406d6ac262 clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGExprScalar.cpp:5882:3
#23 0x000056406d4eb0b5 clang::CodeGen::CodeGenFunction::EmitReturnStmt(clang::ReturnStmt const&) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGStmt.cpp:1698:26
#24 0x000056406d4e744f clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGStmt.cpp:163:75
#25 0x000056406d4f1733 clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CGStmt.cpp:591:3
#26 0x000056406d4bca3f clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenFunction.cpp:1376:5
#27 0x000056406d4bdbe6 clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenFunction.cpp:1629:3
#28 0x000056406d2847df clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenModule.cpp:6401:3
#29 0x000056406d27b1ac clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenModule.cpp:4484:12
#30 0x000056406d280545 clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenModule.cpp:4195:5
#31 0x000056406d2798e8 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenModule.cpp:7309:5
#32 0x000056406d28b971 clang::CodeGen::CodeGenModule::EmitDeclContext(clang::DeclContext const*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenModule.cpp:7280:16
#33 0x000056406d279a55 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenModule.cpp:7338:5
#34 0x000056406dc73462 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/ModuleBuilder.cpp:195:20
#35 0x000056406dc62831 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenAction.cpp:171:8
#36 0x00005640708caa93 clang::ParseAST(clang::Sema&, bool, bool) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/Parse/ParseAST.cpp:174:11
#37 0x000056406e42fb29 clang::ASTFrontendAction::ExecuteAction() /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/Frontend/FrontendAction.cpp:1436:1
#38 0x000056406dc671ed clang::CodeGenAction::ExecuteAction() /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/CodeGen/CodeGenAction.cpp:1110:5
#39 0x000056406e42f506 clang::FrontendAction::Execute() /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/Frontend/FrontendAction.cpp:1318:7
#40 0x000056406e33e173 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/Frontend/CompilerInstance.cpp:1007:23
#41 0x000056406e6125c5 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) /usr/local/google/home/ayzhao/src/llvm-project/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:310:8
#42 0x000056406a512c8a cc1_main(llvm::ArrayRef<char const*>, char const*, void*) /usr/local/google/home/ayzhao/src/llvm-project/clang/tools/driver/cc1_main.cpp:300:13
#43 0x000056406a5061c8 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>) /usr/local/google/home/ayzhao/src/llvm-project/clang/tools/driver/driver.cpp:225:5
#44 0x000056406a504fb1 clang_main(int, char**, llvm::ToolContext const&) /usr/local/google/home/ayzhao/src/llvm-project/clang/tools/driver/driver.cpp:268:5
#45 0x000056406a538fd5 main /usr/local/google/home/ayzhao/src/llvm-project/build-debug/tools/clang/tools/driver/clang-driver.cpp:17:3
#46 0x00007f81e2633ca8 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#47 0x00007f81e2633d65 call_init ./csu/../csu/libc-start.c:128:20
#48 0x00007f81e2633d65 __libc_start_main ./csu/../csu/libc-start.c:347:5
#49 0x000056406a504a21 _start (/usr/local/google/home/ayzhao/src/llvm-project/build-debug/bin/clang-21+0x64afa21)
clang: error: unable to execute command: Aborted (core dumped)
clang: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 22.0.0git ([email protected]:llvm/llvm-project.git 71365c0b6b95eb6874b08f32fe58b5419979ff4c)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/google/home/ayzhao/src/llvm-project/build-debug/bin
Build config: +unoptimized, +assertions
clang: note: diagnostic msg: Error generating preprocessed source(s) - no preprocessable inputs.

alanzhao1 · 2025-10-02T00:49:37Z

Heads up - this PR is causing us to hit the following assertion in https://github.com/google/highway. I'm currently running cvise to get a minimal reproducer.

The repro file is 2.5M, so cvise will take forever. This will take a while, so I apologize in advance.

alanzhao1 · 2025-10-02T08:53:14Z

Reduced repro:

constexpr long kAlignment = 128;
long AllocateAlignedBytes_payload;
void AllocateAlignedBytes() {
  __builtin_assume_aligned(
      reinterpret_cast<void *>(AllocateAlignedBytes_payload), kAlignment);
}

cor3ntin · 2025-10-02T13:28:54Z

@tbaederr

…stantExpr (llvm#161314)" This reverts commit 8f77621.

DKLoehr · 2025-10-02T18:43:15Z

Since this is a crash and it's blocking us from finding any other issues at chromium, let's revert this for now.

erichkeane · 2025-10-02T18:55:49Z

Since this is a crash and it's blocking us from finding any other issues at chromium, let's revert this for now.

That sounds unfortunate but reasonable. Thanks for handling the revert.

erichkeane · 2025-10-02T19:07:18Z

@Fznamznon : Your patch 9ad72df seems at least closely related here: in CGExprScalar.cpp in VisitConstantExpr.

This patch is unfortunately just revealing a bug there, where the type of the constant expression is a L value constant but isn't getting the 'pointer' type for the EmitLoadOfScalar.

It isn't clear to me what SHOULD happen, but that at least seems wrong.

…stantExpr (#161314)" (#161719) This reverts commit 8f77621 (#161314). Reason: Causing crashes when building https://github.com/google/highway. See the original PR for details.

llvm#161314) Since the second argument must be a constant integer, we can as well convert it to a `ConstantExpr` in Sema. Fixes llvm#161272

…stantExpr (llvm#161314)" (llvm#161719) This reverts commit 8f77621 (llvm#161314). Reason: Causing crashes when building https://github.com/google/highway. See the original PR for details.

tbaederr · 2025-10-04T04:21:59Z

It seems like we're doing the load in VisitConstantExpr manually, even though that's already happened in this case, because that's what we do in evaluateAsRValue.

…nstantExpr (llvm#161314)" (llvm#161719) This reverts commit f1650cf.

#161945) …nstantExpr (#161314)" (#161719) This reverts commit f1650cf.

llvm#161945) …nstantExpr (llvm#161314)" (llvm#161719) This reverts commit f1650cf.

tbaederr requested review from cor3ntin, efriedma-quic and erichkeane September 30, 2025 04:53

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" labels Sep 30, 2025

cor3ntin approved these changes Sep 30, 2025

View reviewed changes

[clang] Convert second arg of __builtin_assume_aligned to ConstantExpr

b442ffb

tbaederr force-pushed the assume-aligned branch from 607da57 to b442ffb Compare October 1, 2025 14:01

tbaederr merged commit 8f77621 into llvm:main Oct 1, 2025
8 of 10 checks passed

DKLoehr added a commit to DKLoehr/llvm-project that referenced this pull request Oct 2, 2025

Revert "[clang] Convert second arg of __builtin_assume_aligned to Con…

48727f1

…stantExpr (llvm#161314)" This reverts commit 8f77621.

DKLoehr mentioned this pull request Oct 2, 2025

Revert "[clang] Convert second arg of __builtin_assume_aligned to ConstantExpr (#161314)" #161719

Merged

tbaederr mentioned this pull request Oct 4, 2025

Reapply "[clang] Convert second arg of __builtin_assume_aligned to Co… #161945

Merged

tbaederr added a commit to tbaederr/llvm-project that referenced this pull request Oct 4, 2025

Reapply "[clang] Convert second arg of __builtin_assume_aligned to Co…

089e1e1

…nstantExpr (llvm#161314)" (llvm#161719) This reverts commit f1650cf.

tbaederr added a commit that referenced this pull request Oct 5, 2025

Reapply "[clang] Convert second arg of __builtin_assume_aligned to Co… (

8dac6e2

#161945) …nstantExpr (#161314)" (#161719) This reverts commit f1650cf.

aokblast pushed a commit to aokblast/llvm-project that referenced this pull request Oct 6, 2025

Reapply "[clang] Convert second arg of __builtin_assume_aligned to Co… (

3b9956d

llvm#161945) …nstantExpr (llvm#161314)" (llvm#161719) This reverts commit f1650cf.

aemerson mentioned this pull request Oct 16, 2025

[clang-reorder-fields] Check for flexible array member (#160262) #163697

Closed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

[clang] Convert second arg of __builtin_assume_aligned to ConstantExpr #161314

[clang] Convert second arg of __builtin_assume_aligned to ConstantExpr #161314

Uh oh!

tbaederr commented Sep 30, 2025

Uh oh!

llvmbot commented Sep 30, 2025

Uh oh!

cor3ntin commented Sep 30, 2025

Uh oh!

Uh oh!

alanzhao1 commented Oct 1, 2025

Uh oh!

alanzhao1 commented Oct 2, 2025

Uh oh!

alanzhao1 commented Oct 2, 2025

Uh oh!

cor3ntin commented Oct 2, 2025

Uh oh!

DKLoehr commented Oct 2, 2025

Uh oh!

erichkeane commented Oct 2, 2025

Uh oh!

erichkeane commented Oct 2, 2025

Uh oh!

tbaederr commented Oct 4, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

[clang] Convert second arg of __builtin_assume_aligned to ConstantExpr #161314

[clang] Convert second arg of __builtin_assume_aligned to ConstantExpr #161314

Uh oh!

Conversation

tbaederr commented Sep 30, 2025

Uh oh!

llvmbot commented Sep 30, 2025

Uh oh!

cor3ntin commented Sep 30, 2025

Uh oh!

Uh oh!

alanzhao1 commented Oct 1, 2025

Uh oh!

alanzhao1 commented Oct 2, 2025

Uh oh!

alanzhao1 commented Oct 2, 2025

Uh oh!

cor3ntin commented Oct 2, 2025

Uh oh!

DKLoehr commented Oct 2, 2025

Uh oh!

erichkeane commented Oct 2, 2025

Uh oh!

erichkeane commented Oct 2, 2025

Uh oh!

tbaederr commented Oct 4, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants