[llvm] r212337 - GlobalDCE: Delete available_externally initializers if it allows removing the value the initializer is referring to.
Pete Cooper
peter_cooper at apple.com
Tue Jul 8 10:15:07 PDT 2014
> On Jul 8, 2014, at 6:03 PM, Pete Cooper <peter_cooper at apple.com> wrote:
>
>>
>> On Jul 7, 2014, at 10:28 PM, Benjamin Kramer <benny.kra at gmail.com> wrote:
>>
>>
>> On 07.07.2014, at 20:20, Pete Cooper <pete.cooper at gmail.com> wrote:
>>
>>> Hey Ben
>>>
>>> This is crashing our test suite. Mind taking a look? This may be related to what Richard has just pointed out too.
>>
>> I think this is something different. Feel free to revert if this is blocking you in the meantime.
> Thanks Ben. I’m able to repro the crash for the attached file, and have it pass, just by reverting.
>
> Going to do that now.
Reverted as r212550.
>
> Thanks,
> Pete
>>
>> - Ben
>>
>>>
>>> Attached a reduced test which crashes the following "opt dce.ll -globaldce -o file.bc”
>>>
>>> Cheers,
>>> Pete
>>>
>>>
>>>
>>>
>>> On Fri, Jul 4, 2014 at 1:36 PM, Benjamin Kramer <benny.kra at googlemail.com> wrote:
>>> Author: d0k
>>> Date: Fri Jul 4 07:36:05 2014
>>> New Revision: 212337
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=212337&view=rev
>>> Log:
>>> GlobalDCE: Delete available_externally initializers if it allows removing the value the initializer is referring to.
>>>
>>> This is useful for functions that are not actually available externally but
>>> referenced by a vtable of some kind. Clang emits functions like this for the MS
>>> ABI.
>>>
>>> PR20182.
>>>
>>> Modified:
>>> llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp
>>> llvm/trunk/test/Transforms/GlobalDCE/externally_available.ll
>>>
>>> Modified: llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp?rev=212337&r1=212336&r2=212337&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp (original)
>>> +++ llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp Fri Jul 4 07:36:05 2014
>>> @@ -44,14 +44,19 @@ namespace {
>>> bool runOnModule(Module &M) override;
>>>
>>> private:
>>> - SmallPtrSet<GlobalValue*, 32> AliveGlobals;
>>> + SmallPtrSet<Constant *, 32> AliveGlobals;
>>> SmallPtrSet<Constant *, 8> SeenConstants;
>>> + SmallPtrSet<GlobalVariable *, 8> DiscardableGlobalInitializers;
>>>
>>> /// GlobalIsNeeded - mark the specific global value as needed, and
>>> /// recursively mark anything that it uses as also needed.
>>> void GlobalIsNeeded(GlobalValue *GV);
>>> void MarkUsedGlobalsAsNeeded(Constant *C);
>>>
>>> + /// \brief Checks if C is alive or is a ConstantExpr that refers to an alive
>>> + /// value.
>>> + bool ContainsUsedGlobal(Constant *C);
>>> +
>>> bool RemoveUnusedGlobalValue(GlobalValue &GV);
>>> };
>>> }
>>> @@ -162,6 +167,19 @@ bool GlobalDCE::runOnModule(Module &M) {
>>> I->setAliasee(nullptr);
>>> }
>>>
>>> + // Look for available externally constants that we can turn into normal
>>> + // externals by deleting their initalizers. This allows us to remove other
>>> + // globals that are referenced by the initializer.
>>> + if (!DiscardableGlobalInitializers.empty()) {
>>> + for (GlobalVariable *GV : DiscardableGlobalInitializers) {
>>> + if (!ContainsUsedGlobal(GV->getInitializer())) {
>>> + GV->setInitializer(nullptr);
>>> + GV->setLinkage(GlobalValue::ExternalLinkage);
>>> + Changed = true;
>>> + }
>>> + }
>>> + }
>>> +
>>> if (!DeadFunctions.empty()) {
>>> // Now that all interferences have been dropped, delete the actual objects
>>> // themselves.
>>> @@ -209,8 +227,12 @@ void GlobalDCE::GlobalIsNeeded(GlobalVal
>>> if (GlobalVariable *GV = dyn_cast<GlobalVariable>(G)) {
>>> // If this is a global variable, we must make sure to add any global values
>>> // referenced by the initializer to the alive set.
>>> - if (GV->hasInitializer())
>>> - MarkUsedGlobalsAsNeeded(GV->getInitializer());
>>> + if (GV->hasInitializer()) {
>>> + if (GV->hasAvailableExternallyLinkage())
>>> + DiscardableGlobalInitializers.insert(GV);
>>> + else
>>> + MarkUsedGlobalsAsNeeded(GV->getInitializer());
>>> + }
>>> } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(G)) {
>>> // The target of a global alias is needed.
>>> MarkUsedGlobalsAsNeeded(GA->getAliasee());
>>> @@ -248,6 +270,21 @@ void GlobalDCE::MarkUsedGlobalsAsNeeded(
>>> }
>>> }
>>>
>>> +bool GlobalDCE::ContainsUsedGlobal(Constant *C) {
>>> + // C contains a used global If C is alive or we visited it while marking
>>> + // values alive.
>>> + if (AliveGlobals.count(C) || SeenConstants.count(C))
>>> + return true;
>>> +
>>> + // Now check all operands of a ConstantExpr.
>>> + for (User::op_iterator I = C->op_begin(), E = C->op_end(); I != E; ++I) {
>>> + Constant *Op = dyn_cast<Constant>(*I);
>>> + if (Op && ContainsUsedGlobal(Op))
>>> + return true;
>>> + }
>>> + return false;
>>> +}
>>> +
>>> // RemoveUnusedGlobalValue - Loop over all of the uses of the specified
>>> // GlobalValue, looking for the constant pointer ref that may be pointing to it.
>>> // If found, check to see if the constant pointer ref is safe to destroy, and if
>>>
>>> Modified: llvm/trunk/test/Transforms/GlobalDCE/externally_available.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GlobalDCE/externally_available.ll?rev=212337&r1=212336&r2=212337&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/GlobalDCE/externally_available.ll (original)
>>> +++ llvm/trunk/test/Transforms/GlobalDCE/externally_available.ll Fri Jul 4 07:36:05 2014
>>> @@ -1,10 +1,43 @@
>>> -; RUN: opt < %s -globaldce -S | not grep test_
>>> +; RUN: opt < %s -globaldce -S | FileCheck %s
>>>
>>> ; test_function should not be emitted to the .s file.
>>> +; CHECK-NOT: @test_function
>>> define available_externally i32 @test_function() {
>>> ret i32 4
>>> }
>>>
>>> ; test_global should not be emitted to the .s file.
>>> +; CHECK-NOT: @test_global
>>> @test_global = available_externally global i32 4
>>>
>>> +; CHECK: @x = external constant void ()*
>>> + at x = available_externally constant void()* @f
>>> +; CHECK: @y = external constant i32
>>> + at y = available_externally constant i32 ptrtoint (void()* @g to i32)
>>> +; @h is still alive, so don't remove the initializer too eagerly.
>>> +; CHECK: @z = available_externally constant i8 ptrtoint (void (i8)* @h to i8)
>>> + at z = available_externally constant i8 ptrtoint (void(i8)* @h to i8)
>>> +
>>> +; CHECK-NOT: @f
>>> +define linkonce_odr void @f() {
>>> + ret void
>>> +}
>>> +
>>> +; CHECK-NOT: @g
>>> +define linkonce_odr void @g() {
>>> + ret void
>>> +}
>>> +
>>> +; CHECK: define linkonce_odr void @h
>>> +define linkonce_odr void @h(i8) {
>>> + ret void
>>> +}
>>> +
>>> +define i32 @main() {
>>> + %f = load void()** @x
>>> + call void %f()
>>> + %g = load i32* @y
>>> + %h = load i8* @z
>>> + call void @h(i8 %h)
>>> + ret i32 %g
>>> +}
>>>
>>>
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>>
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