[clang] Convert second arg of __builtin_assume_aligned to ConstantExpr #161314
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@llvm/pr-subscribers-clang Author: Timm Baeder (tbaederr) ChangesSince the second argument must be a constant integer, we can as well convert it to a Fixes #161272 Full diff: https://github.com/llvm/llvm-project/pull/161314.diff 2 Files Affected:
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}}
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Can you add a changelog entry? Thanks |
cor3ntin
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Sep 30, 2025
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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. |
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Reduced repro: constexpr long kAlignment = 128;
long AllocateAlignedBytes_payload;
void AllocateAlignedBytes() {
__builtin_assume_aligned(
reinterpret_cast<void *>(AllocateAlignedBytes_payload), kAlignment);
} |
DKLoehr
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Oct 2, 2025
…stantExpr (llvm#161314)" This reverts commit 8f77621.
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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. |
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@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 It isn't clear to me what SHOULD happen, but that at least seems wrong. |
DKLoehr
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…stantExpr (#161314)" (#161719) This reverts commit 8f77621 (#161314). Reason: Causing crashes when building https://github.com/google/highway. See the original PR for details.
mahesh-attarde
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Oct 3, 2025
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
mahesh-attarde
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Oct 3, 2025
…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.
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Since the second argument must be a constant integer, we can as well convert it to a
ConstantExprin Sema.Fixes #161272