[llvm] r351520 - Re-enable terminator folding in LoopSimplifyCFG: underlying bugs fixed

[Maxim Kazantsev via llvm-commits]

Thanks for reverting it Jordan! I’ll take a look.

--Max

From: Jordan Rupprecht <rupprecht at google.com>
Sent: Wednesday, January 23, 2019 8:15 AM
To: Maxim Kazantsev <max.kazantsev at azul.com>
Cc: llvm-commits at lists.llvm.org
Subject: Re: [llvm] r351520 - Re-enable terminator folding in LoopSimplifyCFG: underlying bugs fixed

Here's the creduce + stack trace w/ a debug build:

$ cat /tmp/repro.c
int a, b, *c, d, e;
void f() {
  int g;
  for (;;) {
    for (; e; e = b) {
      c = g;
      for (; c; c = d)
        if (a) break;
      if (c) break;
    }
  }
}

$ clang -O1 -fexperimental-new-pass-manager -mllvm -enable-loop-simplifycfg-term-folding -c /tmp/repro.c
clang-9: ~/src/llvm-project/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp:63: void llvm::DeleteDeadBlocks(SmallVectorImpl<llvm::BasicBlock *> &, llvm::DomTreeUpdater *): Assertion
`Dead.count(Pred) && "All predecessors must be dead!"' failed.
...
 #9 0x00007f448da1723b llvm::DeleteDeadBlocks(llvm::SmallVectorImpl<llvm::BasicBlock*>&, llvm::DomTreeUpdater*) ~/src/llvm-project/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp:62:
5
#10 0x00007f448e5c67ab (anonymous namespace)::ConstantTerminatorFoldingImpl::deleteDeadLoopBlocks() ~/src/llvm-project/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp:415:5

On Tue, Jan 22, 2019 at 9:43 AM Jordan Rupprecht <rupprecht at google.com<mailto:rupprecht at google.com>> wrote:
It looks like this is still causing crashes, so I've temporarily reverted this as https://reviews.llvm.org/rL351845. I hope to have a repro later today.

On Thu, Jan 17, 2019 at 9:01 PM Max Kazantsev via llvm-commits <llvm-commits at lists.llvm.org<mailto:llvm-commits at lists.llvm.org>> wrote:
Author: mkazantsev
Date: Thu Jan 17 20:57:32 2019
New Revision: 351520

URL: http://llvm.org/viewvc/llvm-project?rev=351520&view=rev
Log:
Re-enable terminator folding in LoopSimplifyCFG: underlying bugs fixed

Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp?rev=351520&r1=351519&r2=351520&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp Thu Jan 17 20:57:32 2019
@@ -42,7 +42,7 @@ using namespace llvm;
 #define DEBUG_TYPE "loop-simplifycfg"

 static cl::opt<bool> EnableTermFolding("enable-loop-simplifycfg-term-folding",
-                                       cl::init(false));
+                                       cl::init(true));

 STATISTIC(NumTerminatorsFolded,
           "Number of terminators folded to unconditional branches");


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