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

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/161314

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


Fixes https://github.com/llvm/llvm-project/issues/161272

>From 607da5771cb8cc47bf6b6f0efe023dee65470e7d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Tue, 30 Sep 2025 06:48:16 +0200
Subject: [PATCH] [clang] Convert second arg of __builtin_assume_aligned to
 ConstantExpr

---
 clang/lib/Sema/SemaChecking.cpp               | 3 +++
 clang/test/SemaCXX/builtin-assume-aligned.cpp | 6 ++++++
 2 files changed, 9 insertions(+)

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}}