[llvm] [LLVM] Maintain element type of @llvm.compiler.used/@llvm.used if it already exists (PR #162660)
Juan Manuel Martinez Caamaño via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 9 07:04:47 PDT 2025
https://github.com/jmmartinez created https://github.com/llvm/llvm-project/pull/162660
At the moment, the address space for the pointer stored in the `llvm.compiler.used/llvm.used` is not well defined:
1. Clang uses the language default address space,
2. LLVM helpers from `ModuleUtils` use the 0 address space,
3. and BitcodeWriter (for fembed-bitcode) tries to preserve the element type if it already exists, 0 otherwise.
This PR doesn't solve this issue. It only adds one test that documents one problem with it, and makes the BitcodeWriter use the llvm helpers to reduce the places where these variables change.
Without this patch, the test added in the PR fails with an assertion:
```
UtilsTests: /home/juamarti/llvm/_llvm/llvm/lib/IR/Constants.cpp:1327:
static Constant *llvm::ConstantArray::getImpl(ArrayType *, ArrayRef<Constant *>):
Assertion `C->getType() == Ty->getElementType() && "Wrong type in array element initializer"' failed.
```
>From 31708bff5da7b79d69ec7c6abee5f5362219165e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juan=20Manuel=20Martinez=20Caama=C3=B1o?= <juamarti at amd.com>
Date: Thu, 9 Oct 2025 14:57:56 +0200
Subject: [PATCH 1/3] Pre-Commit test: [LLVM] Maintain element type of
@llvm.compiler.used/@llvm.used if it already exists
This new test fails with:
/home/juamarti/llvm/_llvm/llvm/lib/IR/Constants.cpp:1327:
static Constant *llvm::ConstantArray::getImpl(ArrayType *, ArrayRef<Constant *>):
Assertion `C->getType() == Ty->getElementType()
&& "Wrong type in array element initializer"'
failed.
---
.../Transforms/Utils/ModuleUtilsTest.cpp | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/llvm/unittests/Transforms/Utils/ModuleUtilsTest.cpp b/llvm/unittests/Transforms/Utils/ModuleUtilsTest.cpp
index d4094c5307060..0cc408af43bc5 100644
--- a/llvm/unittests/Transforms/Utils/ModuleUtilsTest.cpp
+++ b/llvm/unittests/Transforms/Utils/ModuleUtilsTest.cpp
@@ -69,6 +69,23 @@ TEST(ModuleUtils, AppendToUsedList2) {
EXPECT_EQ(1, getListSize(*M, "llvm.used"));
}
+TEST(ModuleUtils, AppendToUsedList3) {
+ LLVMContext C;
+
+ std::unique_ptr<Module> M = parseIR(C, R"(
+ @x = addrspace(1) global [2 x i32] zeroinitializer, align 4
+ @y = addrspace(2) global [2 x i32] zeroinitializer, align 4
+ @llvm.compiler.used = appending global [1 x ptr addrspace (3)] [ptr addrspace(3) addrspacecast (ptr addrspace (1) @x to ptr addrspace(3))]
+ )");
+ GlobalVariable *X = M->getNamedGlobal("x");
+ GlobalVariable *Y = M->getNamedGlobal("y");
+ EXPECT_EQ(1, getListSize(*M, "llvm.compiler.used"));
+ appendToCompilerUsed(*M, X);
+ EXPECT_EQ(1, getListSize(*M, "llvm.compiler.used"));
+ appendToCompilerUsed(*M, Y);
+ EXPECT_EQ(2, getListSize(*M, "llvm.compiler.used"));
+}
+
using AppendFnType = decltype(&appendToGlobalCtors);
using TransformFnType = decltype(&transformGlobalCtors);
using ParamType = std::tuple<StringRef, AppendFnType, TransformFnType>;
>From 3e57943ecd237c86e0f49d398e1da7cbcd14cdf0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juan=20Manuel=20Martinez=20Caama=C3=B1o?= <juamarti at amd.com>
Date: Thu, 9 Oct 2025 14:34:32 +0200
Subject: [PATCH 2/3] [LLVM] Maintain element type of
@llvm.compiler.used/@llvm.used if it already exists
At the moment, the pointer type stored in the
llvm.compiler.used/llvm.used is not well fixed.
The frontend uses a pointer to the default address space (which may not
be 0; for example, it is 4 for SPIRV).
This patch makes `appendToUsed/appendToCompilerUsed` match the behaviour
in BitcodeWriter.cpp: if the variable already exists, preserve its
element type, otherwise use `ptr addrspace (0)`.
This fixes the following error in the newly added test:
UtilsTests: /home/juamarti/llvm/_llvm/llvm/lib/IR/Constants.cpp:1327:
static Constant *llvm::ConstantArray::getImpl(ArrayType *, ArrayRef<Constant *>):
Assertion `C->getType() == Ty->getElementType() && "Wrong type in array element initializer"' failed.
---
llvm/lib/Transforms/Utils/ModuleUtils.cpp | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/llvm/lib/Transforms/Utils/ModuleUtils.cpp b/llvm/lib/Transforms/Utils/ModuleUtils.cpp
index 596849ecab742..d1acb0ff1ad6b 100644
--- a/llvm/lib/Transforms/Utils/ModuleUtils.cpp
+++ b/llvm/lib/Transforms/Utils/ModuleUtils.cpp
@@ -138,10 +138,11 @@ static void appendToUsedList(Module &M, StringRef Name, ArrayRef<GlobalValue *>
SmallSetVector<Constant *, 16> Init;
collectUsedGlobals(GV, Init);
+ Type *ArrayEltTy = GV ? GV->getValueType()->getArrayElementType()
+ : PointerType::getUnqual(M.getContext());
if (GV)
GV->eraseFromParent();
- Type *ArrayEltTy = llvm::PointerType::getUnqual(M.getContext());
for (auto *V : Values)
Init.insert(ConstantExpr::getPointerBitCastOrAddrSpaceCast(V, ArrayEltTy));
>From 3d08e3aad6e6ba236c663cb2ab390a3a413f66e0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juan=20Manuel=20Martinez=20Caama=C3=B1o?= <juamarti at amd.com>
Date: Thu, 9 Oct 2025 14:34:24 +0200
Subject: [PATCH 3/3] [NFC][BitcodeWriter] Use appendToCompilerUsed instead of
custom implementation
---
llvm/lib/Bitcode/Writer/BitcodeWriter.cpp | 70 ++++++++++-------------
llvm/lib/Bitcode/Writer/CMakeLists.txt | 1 +
2 files changed, 31 insertions(+), 40 deletions(-)
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 7ed140d392fca..f7afa393f3e00 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -75,6 +75,7 @@
#include "llvm/Support/SHA1.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TargetParser/Triple.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
@@ -5850,25 +5851,25 @@ static const char *getSectionNameForCommandline(const Triple &T) {
void llvm::embedBitcodeInModule(llvm::Module &M, llvm::MemoryBufferRef Buf,
bool EmbedBitcode, bool EmbedCmdline,
const std::vector<uint8_t> &CmdArgs) {
- // Save llvm.compiler.used and remove it.
- SmallVector<Constant *, 2> UsedArray;
- SmallVector<GlobalValue *, 4> UsedGlobals;
- GlobalVariable *Used = collectUsedGlobalVariables(M, UsedGlobals, true);
- Type *UsedElementType = Used ? Used->getValueType()->getArrayElementType()
- : PointerType::getUnqual(M.getContext());
- for (auto *GV : UsedGlobals) {
- if (GV->getName() != "llvm.embedded.module" &&
- GV->getName() != "llvm.cmdline")
- UsedArray.push_back(
- ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
- }
- if (Used)
- Used->eraseFromParent();
// Embed the bitcode for the llvm module.
std::string Data;
ArrayRef<uint8_t> ModuleData;
Triple T(M.getTargetTriple());
+ SmallVector<GlobalValue *, 2> NewGlobals;
+
+ auto IsCmdOrBitcode = [&](Constant *C) {
+ GlobalVariable *GV = dyn_cast<GlobalVariable>(C);
+ StringRef Name = GV ? GV->getName() : "";
+ if (EmbedBitcode && Name == "llvm.embedded.module")
+ return true;
+ if (EmbedCmdline && Name == "llvm.cmdline")
+ return true;
+ return false;
+ };
+
+ if (EmbedBitcode || EmbedCmdline)
+ removeFromUsedLists(M, IsCmdOrBitcode);
if (EmbedBitcode) {
if (Buf.getBufferSize() == 0 ||
@@ -5887,23 +5888,22 @@ void llvm::embedBitcodeInModule(llvm::Module &M, llvm::MemoryBufferRef Buf,
}
llvm::Constant *ModuleConstant =
llvm::ConstantDataArray::get(M.getContext(), ModuleData);
- llvm::GlobalVariable *GV = new llvm::GlobalVariable(
+ llvm::GlobalVariable *EmbeddedModule = new llvm::GlobalVariable(
M, ModuleConstant->getType(), true, llvm::GlobalValue::PrivateLinkage,
ModuleConstant);
- GV->setSection(getSectionNameForBitcode(T));
+ EmbeddedModule->setSection(getSectionNameForBitcode(T));
// Set alignment to 1 to prevent padding between two contributions from input
// sections after linking.
- GV->setAlignment(Align(1));
- UsedArray.push_back(
- ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
+ EmbeddedModule->setAlignment(Align(1));
+ NewGlobals.push_back(EmbeddedModule);
if (llvm::GlobalVariable *Old =
M.getGlobalVariable("llvm.embedded.module", true)) {
assert(Old->hasZeroLiveUses() &&
"llvm.embedded.module can only be used once in llvm.compiler.used");
- GV->takeName(Old);
+ EmbeddedModule->takeName(Old);
Old->eraseFromParent();
} else {
- GV->setName("llvm.embedded.module");
+ EmbeddedModule->setName("llvm.embedded.module");
}
// Skip if only bitcode needs to be embedded.
@@ -5913,30 +5913,20 @@ void llvm::embedBitcodeInModule(llvm::Module &M, llvm::MemoryBufferRef Buf,
CmdArgs.size());
llvm::Constant *CmdConstant =
llvm::ConstantDataArray::get(M.getContext(), CmdData);
- GV = new llvm::GlobalVariable(M, CmdConstant->getType(), true,
- llvm::GlobalValue::PrivateLinkage,
- CmdConstant);
- GV->setSection(getSectionNameForCommandline(T));
- GV->setAlignment(Align(1));
- UsedArray.push_back(
- ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
+ GlobalVariable *CmdLine = new llvm::GlobalVariable(
+ M, CmdConstant->getType(), true, llvm::GlobalValue::PrivateLinkage,
+ CmdConstant);
+ CmdLine->setSection(getSectionNameForCommandline(T));
+ CmdLine->setAlignment(Align(1));
if (llvm::GlobalVariable *Old = M.getGlobalVariable("llvm.cmdline", true)) {
assert(Old->hasZeroLiveUses() &&
"llvm.cmdline can only be used once in llvm.compiler.used");
- GV->takeName(Old);
+ CmdLine->takeName(Old);
Old->eraseFromParent();
} else {
- GV->setName("llvm.cmdline");
+ CmdLine->setName("llvm.cmdline");
}
+ NewGlobals.push_back(CmdLine);
+ appendToCompilerUsed(M, NewGlobals);
}
-
- if (UsedArray.empty())
- return;
-
- // Recreate llvm.compiler.used.
- ArrayType *ATy = ArrayType::get(UsedElementType, UsedArray.size());
- auto *NewUsed = new GlobalVariable(
- M, ATy, false, llvm::GlobalValue::AppendingLinkage,
- llvm::ConstantArray::get(ATy, UsedArray), "llvm.compiler.used");
- NewUsed->setSection("llvm.metadata");
}
diff --git a/llvm/lib/Bitcode/Writer/CMakeLists.txt b/llvm/lib/Bitcode/Writer/CMakeLists.txt
index 2c508ca9fae95..5bbb872a90341 100644
--- a/llvm/lib/Bitcode/Writer/CMakeLists.txt
+++ b/llvm/lib/Bitcode/Writer/CMakeLists.txt
@@ -15,4 +15,5 @@ add_llvm_component_library(LLVMBitWriter
ProfileData
Support
TargetParser
+ TransformUtils
)
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