[llvm] r350939 - [MergeFunc] Erase unused duplicate functions if they are discardable

[Vedant Kumar via llvm-commits]

This caused buildbot failures in clang/test/CodeGenCXX/merge-functions.cpp. I should have a fix momentarily.

vedant

> On Jan 11, 2019, at 9:56 AM, Vedant Kumar via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: vedantk
> Date: Fri Jan 11 09:56:35 2019
> New Revision: 350939
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=350939&view=rev
> Log:
> [MergeFunc] Erase unused duplicate functions if they are discardable
> 
> MergeFunc only deletes unused duplicate functions if they have local
> linkage, but it should be safe to relax this to any "discardable if
> unused" linkage type.
> 
> Differential Revision: https://reviews.llvm.org/D56574
> 
> Modified:
>    llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp
>    llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll
> 
> Modified: llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp?rev=350939&r1=350938&r2=350939&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp Fri Jan 11 09:56:35 2019
> @@ -845,7 +845,7 @@ void MergeFunctions::mergeTwoFunctions(F
>     // If G was internal then we may have replaced all uses of G with F. If so,
>     // stop here and delete G. There's no need for a thunk. (See note on
>     // MergeFunctionsPDI above).
> -    if (G->hasLocalLinkage() && G->use_empty() && !MergeFunctionsPDI) {
> +    if (G->isDiscardableIfUnused() && G->use_empty() && !MergeFunctionsPDI) {
>       G->eraseFromParent();
>       ++NumFunctionsMerged;
>       return;
> 
> Modified: llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll?rev=350939&r1=350938&r2=350939&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll (original)
> +++ llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll Fri Jan 11 09:56:35 2019
> @@ -1,4 +1,4 @@
> -; RUN: opt -S -mergefunc < %s | FileCheck %s
> +; RUN: opt -S -mergefunc < %s | FileCheck %s -implicit-check-not=funC
> 
> ; Replacments should be totally ordered on the function name.
> ; If we don't do this we  can end up with one module defining a thunk for @funA
> @@ -15,6 +15,13 @@
> ; CHECK-NEXT:    tail call i32 @funA(i32 %0, i32 %1)
> ; CHECK-NEXT:    ret
> 
> +define linkonce_odr i32 @funC(i32 %x, i32 %y) {
> +  %sum = add i32 %x, %y
> +  %sum2 = add i32 %x, %sum
> +  %sum3 = add i32 %x, %sum2
> +  ret i32 %sum3
> +}
> +
> define linkonce_odr i32 @funB(i32 %x, i32 %y) {
>   %sum = add i32 %x, %y
>   %sum2 = add i32 %x, %sum
> @@ -28,3 +35,8 @@ define linkonce_odr i32 @funA(i32 %x, i3
>   %sum3 = add i32 %x, %sum2
>   ret i32 %sum3
> }
> +
> +; This creates a use of @funB, preventing -mergefunc from deleting it.
> +; @funC, however, can safely be deleted as it has no uses, and is discardable
> +; if unused.
> + at take_addr_of_funB = global i8* bitcast (i32 (i32, i32)* @funB to i8*)
> 
> 
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