[llvm] r324943 - [LSR] Avoid UB overflow when examining reuse opportunities

[Eric Christopher via llvm-commits]

It fails with clang on linux as well.

Also, is there no way to do it outside of a builtin?

Probably best to revert for now :)

-eric

On Mon, Feb 12, 2018 at 2:37 PM Craig Topper via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> I'm getting a compile eror after this change. It also doesn't seem
> portable to MSVC
>
> lib/Transforms/Scalar/LoopStrengthReduce.cpp:3944:86: error: cannot
> initialize a parameter of type 'long long *' with an rvalue of type
> 'int64_t *' (aka 'long *')
>     if (__builtin_saddll_overflow(Imms.begin()->first,
> std::prev(Imms.end())->first, &Res))
>
> ~Craig
>
> On Mon, Feb 12, 2018 at 1:49 PM, Gerolf Hoflehner via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: ghoflehner
>> Date: Mon Feb 12 13:49:32 2018
>> New Revision: 324943
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=324943&view=rev
>> Log:
>> [LSR] Avoid UB overflow when examining reuse opportunities
>>
>> Added:
>>     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=324943&r1=324942&r2=324943&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp Mon Feb 12
>> 13:49:32 2018
>> @@ -3939,6 +3939,11 @@ 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;
>>
>> Added: 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=324943&view=auto
>>
>> ==============================================================================
>> --- llvm/trunk/test/CodeGen/X86/loop-strength-reduce-overflow-check.ll
>> (added)
>> +++ llvm/trunk/test/CodeGen/X86/loop-strength-reduce-overflow-check.ll
>> Mon Feb 12 13:49:32 2018
>> @@ -0,0 +1,26 @@
>> +; 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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>
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