[llvm] r212550 - Revert "GlobalDCE: Delete available_externally initializers if it allows removing the value the initializer is referring to."

[David Blaikie]

On Tue, Jul 8, 2014 at 10:06 AM, Pete Cooper <peter_cooper at apple.com> wrote:
> Author: pete
> Date: Tue Jul  8 12:06:03 2014
> New Revision: 212550
>
> URL: http://llvm.org/viewvc/llvm-project?rev=212550&view=rev
> Log:
> Revert "GlobalDCE: Delete available_externally initializers if it allows removing the value the initializer is referring to."
>
> This reverts commit 5b55a47e94e28fbb56d0cd5d72c3db9105c15b4c.

There's a neat script (llvm/utils/git-svn/git-svnrevert) that will
revert a given git commit specified by a hash, but create a commit
message that specifies the SVN revision, so that it's useful to
someone reading the commit message (especially later on when
spelunking through history).

- David

>
> A test case was found to crash after this was applied.  I'll file a bug to track fixing this with the test case needed.
>
> 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=212550&r1=212549&r2=212550&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp Tue Jul  8 12:06:03 2014
> @@ -44,19 +44,14 @@ namespace {
>      bool runOnModule(Module &M) override;
>
>    private:
> -    SmallPtrSet<Constant *, 32> AliveGlobals;
> +    SmallPtrSet<GlobalValue*, 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);
>    };
>  }
> @@ -167,19 +162,6 @@ 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.
> @@ -227,12 +209,8 @@ 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()) {
> -      if (GV->hasAvailableExternallyLinkage())
> -        DiscardableGlobalInitializers.insert(GV);
> -      else
> -        MarkUsedGlobalsAsNeeded(GV->getInitializer());
> -    }
> +    if (GV->hasInitializer())
> +      MarkUsedGlobalsAsNeeded(GV->getInitializer());
>    } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(G)) {
>      // The target of a global alias is needed.
>      MarkUsedGlobalsAsNeeded(GA->getAliasee());
> @@ -270,21 +248,6 @@ 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=212550&r1=212549&r2=212550&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/GlobalDCE/externally_available.ll (original)
> +++ llvm/trunk/test/Transforms/GlobalDCE/externally_available.ll Tue Jul  8 12:06:03 2014
> @@ -1,43 +1,10 @@
> -; RUN: opt < %s -globaldce -S | FileCheck %s
> +; RUN: opt < %s -globaldce -S | not grep test_
>
>  ; 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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