[llvm] r350117 - Temporarily disable term folding in LoopSimplifyCFG, add tests

[Maxim Kazantsev via llvm-commits]

Thanks Mikael, I've checked in this test as https://reviews.llvm.org/rL350119 and will follow-up.

-----Original Message-----
From: Mikael Holmén <mikael.holmen at ericsson.com> 
Sent: Friday, December 28, 2018 4:39 PM
To: Maxim Kazantsev <max.kazantsev at azul.com>; llvm-commits at lists.llvm.org
Subject: Re: [llvm] r350117 - Temporarily disable term folding in LoopSimplifyCFG, add tests

Hi Max,

I found another case that you might want to look at before enabling this again. I noticed that:

  opt -S -o - bbi-22646.ll -loop-simplifycfg -licm

crashes with

opt: ../lib/Transforms/Scalar/LICM.cpp:276: bool (anonymous namespace)::LoopInvariantCodeMotion::runOnLoop(llvm::Loop *, AliasAnalysis *, llvm::LoopInfo *, llvm::DominatorTree *, llvm::TargetLibraryInfo *, llvm::TargetTransformInfo *, llvm::ScalarEvolution *, llvm::MemorySSA *, llvm::OptimizationRemarkEmitter *, bool): Assertion `L->isLCSSAForm(*DT) && "Loop is not in LCSSA form."' failed.

The crash goes away with this patch where you disabled the term folding.

/Mikael

On 12/28/18 7:22 AM, Max Kazantsev via llvm-commits wrote:
> Author: mkazantsev
> Date: Thu Dec 27 22:22:39 2018
> New Revision: 350117
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=350117&view=rev
> Log:
> Temporarily disable term folding in LoopSimplifyCFG, add tests
> 
> Modified:
>      llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
>      
> llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
> 
> Modified: llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
> URL: 
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/L
> oopSimplifyCFG.cpp?rev=350117&r1=350116&r2=350117&view=diff
> ======================================================================
> ========
> --- llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/LoopSimplifyCFG.cpp Thu Dec 27 
> +++ 22:22:39 2018
> @@ -42,7 +42,7 @@ using namespace llvm;
>   #define DEBUG_TYPE "loop-simplifycfg"
>   
>   static cl::opt<bool> EnableTermFolding("enable-loop-simplifycfg-term-folding",
> -                                       cl::init(true));
> +                                       cl::init(false));
>   
>   STATISTIC(NumTerminatorsFolded,
>             "Number of terminators folded to unconditional branches");
> 
> Modified: 
> llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll
> URL: 
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopSim
> plifyCFG/constant-fold-branch.ll?rev=350117&r1=350116&r2=350117&view=d
> iff 
> ======================================================================
> ========
> --- llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll 
> (original)
> +++ llvm/trunk/test/Transforms/LoopSimplifyCFG/constant-fold-branch.ll 
> +++ Thu Dec 27 22:22:39 2018
> @@ -1,4 +1,7 @@
>   ; NOTE: Assertions have been autogenerated by 
> utils/update_test_checks.py
> +; XFAIL: *
> +; Tests complex_dead_subloop_branch and complex_dead_subloop_switch 
> +fail an ; assertion, therefore the CFG simplification is temporarily disabled.
>   ; REQUIRES: asserts
>   ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true -loop-simplifycfg -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s
>   ; RUN: opt -S -enable-loop-simplifycfg-term-folding=true 
> -passes='require<domtree>,loop(simplify-cfg)' -debug-only=loop-simplifycfg -verify-loop-info -verify-dom-info -verify-loop-lcssa 2>&1 < %s | FileCheck %s @@ -2507,3 +2510,59 @@ loop_1_backedge:
>   exit:
>     ret i32 %i
>   }
> +
> +define i32 @complex_dead_subloop_branch(i1 %cond1, i1 %cond2, i1 
> +%cond3) {
> +entry:
> +  br label %loop
> +
> +loop:
> +  br i1 true, label %latch, label %subloop
> +
> +subloop:
> +  br i1 %cond1, label %x, label %y
> +
> +x:
> +  br label %subloop_latch
> +
> +y:
> +  br label %subloop_latch
> +
> +subloop_latch:
> +  %dead_phi = phi i32 [ 1, %x ], [ 2, %y ]
> +  br i1 %cond2, label %latch, label %subloop
> +
> +latch:
> +  %result = phi i32 [ 0, %loop ], [ %dead_phi, %subloop_latch ]
> +  br i1 %cond3, label %loop, label %exit
> +
> +exit:
> +  ret i32 %result
> +}
> +
> +define i32 @complex_dead_subloop_switch(i1 %cond1, i1 %cond2, i1 
> +%cond3) {
> +entry:
> +  br label %loop
> +
> +loop:
> +  switch i32 1, label %latch [ i32 0, label %subloop ]
> +
> +subloop:
> +  br i1 %cond1, label %x, label %y
> +
> +x:
> +  br label %subloop_latch
> +
> +y:
> +  br label %subloop_latch
> +
> +subloop_latch:
> +  %dead_phi = phi i32 [ 1, %x ], [ 2, %y ]
> +  br i1 %cond2, label %latch, label %subloop
> +
> +latch:
> +  %result = phi i32 [ 0, %loop ], [ %dead_phi, %subloop_latch ]
> +  br i1 %cond3, label %loop, label %exit
> +
> +exit:
> +  ret i32 %result
> +}
> 
> 
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