[llvm] r324958 - Revert "[LSR] Avoid UB overflow when examining reuse opportunities"

[Adam Nemet via llvm-commits]

Good idea!

> On Feb 12, 2018, at 3:07 PM, Eric Christopher <echristo at gmail.com> wrote:
> 
> Thanks Adam. Also handy to reply to the original commit that you've done so too :)
> 
> Thanks!
> 
> -eric
> 
> On Mon, Feb 12, 2018 at 2:44 PM Adam Nemet via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Author: anemet
> Date: Mon Feb 12 14:42:13 2018
> New Revision: 324958
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=324958&view=rev <http://llvm.org/viewvc/llvm-project?rev=324958&view=rev>
> Log:
> Revert "[LSR] Avoid UB overflow when examining reuse opportunities"
> 
> This reverts commit r324943.
> 
> Breaking bots, reverting for Gerolf.
> 
> Removed:
>     llvm/trunk/test/CodeGen/X86/loop-strength-reduce-overflow-check.ll
> Modified:
>     llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
> 
> Modified: llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp?rev=324958&r1=324957&r2=324958&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp?rev=324958&r1=324957&r2=324958&view=diff>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp Mon Feb 12 14:42:13 2018
> @@ -3939,11 +3939,6 @@ void LSRInstance::GenerateCrossUseConsta
>      if (Imms.size() == 1)
>        continue;
> 
> -    // UB: Check for overflow
> -    int64_t Res;
> -    if (__builtin_saddll_overflow(Imms.begin()->first, std::prev(Imms.end())->first, &Res))
> -      continue;
> -
>      DEBUG(dbgs() << "Generating cross-use offsets for " << *Reg << ':';
>            for (const auto &Entry : Imms)
>              dbgs() << ' ' << Entry.first;
> 
> Removed: llvm/trunk/test/CodeGen/X86/loop-strength-reduce-overflow-check.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/loop-strength-reduce-overflow-check.ll?rev=324957&view=auto <http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/loop-strength-reduce-overflow-check.ll?rev=324957&view=auto>
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/loop-strength-reduce-overflow-check.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/loop-strength-reduce-overflow-check.ll (removed)
> @@ -1,26 +0,0 @@
> -; RUN: llc < %s -O1 -mtriple=x86_64-unknown-unknown
> -
> -; LSR has to check for overflow to avoid UB when it examines reuse opportunities
> -; Clang built with UBSan would expose the issue in this test case
> -
> -define void @main() {
> -bb:
> -  br label %bb1
> -
> -bb1:                                              ; preds = %bb1, %bb
> -  %tmp = phi i64 [ 248268322795906120, %bb ], [ %tmp10, %bb1 ]
> -  %tmp2 = sub i64 %tmp, 248268322795906120
> -  %tmp3 = getelementptr i8, i8* undef, i64 %tmp2
> -  %tmp4 = sub i64 %tmp, 248268322795906120
> -  %tmp5 = getelementptr i8, i8* undef, i64 %tmp4
> -  %tmp6 = getelementptr i8, i8* %tmp5, i64 -9086989864993762928
> -  %tmp7 = load i8, i8* %tmp6, align 1
> -  %tmp8 = getelementptr i8, i8* %tmp3, i64 -1931736422337600660
> -  store i8 undef, i8* %tmp8
> -  %tmp9 = add i64 %tmp, 248268322795906121
> -  %tmp10 = add i64 %tmp9, -248268322795906120
> -  br i1 undef, label %bb11, label %bb1
> -
> -bb11:                                             ; preds = %bb1
> -  ret void
> -}
> 
> 
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