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[AMDGPU] Re-enable closed-world assumption as an opt-in feature (#115371)

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Although the ABI (if one exists) doesn’t explicitly prohibit
cross-code-object function calls—particularly since our loader can
handle them—such calls are not actually allowed in any of the officially
supported programming models. However, this limitation has some nuances.
For instance, the loader can handle cross-code-object global variables,
which complicates the situation further.

Given this complexity, assuming a closed-world model at link time isn’t
always safe. To address this, this PR introduces an option that enables
this assumption, providing end users the flexibility to enable it for
improved compiler optimizations. However, it is the user’s
responsibility to ensure they do not violate this assumption.
This commit is contained in:
Shilei Tian 2024-12-10 15:57:41 -05:00 committed by GitHub
parent f3c675feec
commit 04269ea0e4
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GPG Key ID: B5690EEEBB952194
3 changed files with 27 additions and 2 deletions
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4
llvm/lib/Target/AMDGPU/AMDGPUAttributor.cpp
View File

@ -1286,6 +1286,10 @@ static bool runImpl(Module &M, AnalysisGetter &AG, TargetMachine &TM,
Attributor A(Functions, InfoCache, AC);
LLVM_DEBUG(dbgs() << "[AMDGPUAttributor] Module " << M.getName() << " is "
<< (AC.IsClosedWorldModule ? "" : "not ")
<< "assumed to be a closed world.\n");
for (auto *F : Functions) {
A.getOrCreateAAFor<AAAMDAttributes>(IRPosition::function(*F));
A.getOrCreateAAFor<AAUniformWorkGroupSize>(IRPosition::function(*F));

13
llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
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@ -454,6 +454,11 @@ static cl::opt<bool> NewRegBankSelect(
"regbankselect"),
cl::init(false), cl::Hidden);
static cl::opt<bool> HasClosedWorldAssumption(
"amdgpu-link-time-closed-world",
cl::desc("Whether has closed-world assumption at link time"),
cl::init(false), cl::Hidden);
extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAMDGPUTarget() {
// Register the target
RegisterTargetMachine<R600TargetMachine> X(getTheR600Target());
@ -859,8 +864,12 @@ void AMDGPUTargetMachine::registerPassBuilderCallbacks(PassBuilder &PB) {
PM.addPass(InternalizePass(mustPreserveGV));
PM.addPass(GlobalDCEPass());
}
if (EnableAMDGPUAttributor)
PM.addPass(AMDGPUAttributorPass(*this));
if (EnableAMDGPUAttributor) {
AMDGPUAttributorOptions Opt;
if (HasClosedWorldAssumption)
Opt.IsClosedWorld = true;
PM.addPass(AMDGPUAttributorPass(*this, Opt));
}
}
});

12
llvm/test/LTO/AMDGPU/closed-world-assumption.ll Normal file
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@ -0,0 +1,12 @@
; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -O3 -debug-only=amdgpu-attributor -o - %s 2>&1 | FileCheck %s --check-prefix=NO-CW
; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -passes="lto<O3>" -debug-only=amdgpu-attributor -o - %s 2>&1 | FileCheck %s --check-prefix=NO-CW
; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -passes="lto<O3>" -debug-only=amdgpu-attributor -amdgpu-link-time-closed-world=1 -o - %s 2>&1 | FileCheck %s --check-prefix=CW
; REQUIRES: amdgpu-registered-target
; REQUIRES: asserts
; NO-CW: Module {{.*}} is not assumed to be a closed world.
; CW: Module {{.*}} is assumed to be a closed world.
define hidden noundef i32 @_Z3foov() {
ret i32 1
}