[llvm] fc93780 - Don't jump to landing pads in Control Flow Optimizer

[Arthur Eubanks via llvm-commits]

Hi Tom, there's a request to merge this bug fix into 10.0.1, is that ok?

On Thu, May 21, 2020 at 3:19 PM Arthur Eubanks via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

>
> Author: Arthur Eubanks
> Date: 2020-05-21T15:19:10-07:00
> New Revision: fc937806efd71eb3803b35d0920bb7d76bc3040b
>
> URL:
> https://github.com/llvm/llvm-project/commit/fc937806efd71eb3803b35d0920bb7d76bc3040b
> DIFF:
> https://github.com/llvm/llvm-project/commit/fc937806efd71eb3803b35d0920bb7d76bc3040b.diff
>
> LOG: Don't jump to landing pads in Control Flow Optimizer
>
> Summary: Likely fixes https://bugs.llvm.org/show_bug.cgi?id=45858.
>
> Subscribers: hiraditya, llvm-commits
>
> Tags: #llvm
>
> Differential Revision: https://reviews.llvm.org/D80047
>
> Added:
>     llvm/test/CodeGen/X86/branchfolding-ehpad.mir
>
> Modified:
>     llvm/lib/CodeGen/BranchFolding.cpp
>
> Removed:
>
>
>
>
> ################################################################################
> diff  --git a/llvm/lib/CodeGen/BranchFolding.cpp
> b/llvm/lib/CodeGen/BranchFolding.cpp
> index eb72542b6efe..852bfb36c720 100644
> --- a/llvm/lib/CodeGen/BranchFolding.cpp
> +++ b/llvm/lib/CodeGen/BranchFolding.cpp
> @@ -921,10 +921,10 @@ bool
> BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
>        continue;
>      }
>
> -    // If one of the blocks is the entire common tail (and not the entry
> -    // block, which we can't jump to), we can treat all blocks with this
> same
> -    // tail at once.  Use PredBB if that is one of the possibilities, as
> that
> -    // will not introduce any extra branches.
> +    // If one of the blocks is the entire common tail (and is not the
> entry
> +    // block/an EH pad, which we can't jump to), we can treat all blocks
> with
> +    // this same tail at once.  Use PredBB if that is one of the
> possibilities,
> +    // as that will not introduce any extra branches.
>      MachineBasicBlock *EntryBB =
>          &MergePotentials.front().getBlock()->getParent()->front();
>      unsigned commonTailIndex = SameTails.size();
> @@ -932,19 +932,21 @@ bool
> BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
>      // into the other.
>      if (SameTails.size() == 2 &&
>
>  SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) &&
> -        SameTails[1].tailIsWholeBlock())
> +        SameTails[1].tailIsWholeBlock() &&
> !SameTails[1].getBlock()->isEHPad())
>        commonTailIndex = 1;
>      else if (SameTails.size() == 2 &&
>               SameTails[1].getBlock()->isLayoutSuccessor(
> -
>  SameTails[0].getBlock()) &&
> -             SameTails[0].tailIsWholeBlock())
> +                 SameTails[0].getBlock()) &&
> +             SameTails[0].tailIsWholeBlock() &&
> +             !SameTails[0].getBlock()->isEHPad())
>        commonTailIndex = 0;
>      else {
>        // Otherwise just pick one, favoring the fall-through predecessor if
>        // there is one.
>        for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
>          MachineBasicBlock *MBB = SameTails[i].getBlock();
> -        if (MBB == EntryBB && SameTails[i].tailIsWholeBlock())
> +        if ((MBB == EntryBB || MBB->isEHPad()) &&
> +            SameTails[i].tailIsWholeBlock())
>            continue;
>          if (MBB == PredBB) {
>            commonTailIndex = i;
>
> diff  --git a/llvm/test/CodeGen/X86/branchfolding-ehpad.mir
> b/llvm/test/CodeGen/X86/branchfolding-ehpad.mir
> new file mode 100644
> index 000000000000..d445cd206803
> --- /dev/null
> +++ b/llvm/test/CodeGen/X86/branchfolding-ehpad.mir
> @@ -0,0 +1,28 @@
> +# RUN: llc -mtriple=x86_64-windows-msvc -verify-machineinstrs -run-pass
> branch-folder -o - %s | FileCheck %s
> +
> +# Check that branch-folder does not create a fallthrough to a landing pad.
> +# Also make sure that the landing pad still can be tail merged.
> +---
> +name: foo
> +body: |
> +  ; CHECK-LABEL: name: foo
> +  bb.0:
> +    successors: %bb.1, %bb.3
> +  bb.1:
> +    JCC_1 %bb.4, 5, implicit killed $eflags
> +  bb.2:
> +    MOV8mi $r13, 1, $noreg, 0, $noreg, 0
> +    JMP_1 %bb.5
> +  ; CHECK: bb.2:
> +  ; CHECK-NOT: successors: {{.*}}bb.3
> +  ; CHECK: bb.3 (landing-pad):
> +  ; CHECK-NOT: MOV8mi
> +  bb.3(landing-pad):
> +    MOV8mi $r13, 1, $noreg, 0, $noreg, 0
> +    JMP_1 %bb.5
> +  ; CHECK: bb.4:
> +  bb.4:
> +    MOV8mi $r13, 2, $noreg, 0, $noreg, 0
> +  bb.5:
> +    RET 0
> +...
>
>
>
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