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miscompile from r248638 #25326

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llvmbot opened this issue Sep 27, 2015 · 5 comments
Closed

miscompile from r248638 #25326

llvmbot opened this issue Sep 27, 2015 · 5 comments
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@llvmbot
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llvmbot commented Sep 27, 2015

Bugzilla Link 24952
Resolution FIXED
Resolved on Sep 27, 2015 16:21
Version unspecified
OS Windows NT
Reporter LLVM Bugzilla Contributor
CC @hfinkel,@sanjoy

Extended Description

The boost example,

#include <boost/multiprecision/cpp_bin_float.hpp>
#include <boost/math/special_functions/gamma.hpp>
#include
int main() {
using namespace boost::multiprecision;
std::cout << boost::math::tgamma(cpp_bin_float_100(1000)) << std::endl;
}

produce correct output

bin/clang++ -O2 -std=c++11 -isystem include cpp_bin_float_snips.cpp
./a.out
4.02387e+2564

with pre-r248638 clang and gcc 5.1.0.

From r248638,

./a.out
terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injectorstd::range_error >'
what(): No bits were set in the operand.

this is on Ubunto 14.04 64 bit, boost 1.57.
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llvmbot commented Sep 27, 2015

assigned to @sanjoy

@sanjoy
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sanjoy commented Sep 27, 2015

I think this is a glitch with how isIdenticalTo is used in
ScalarEvolution.

Can you check if clang built with this patch below fixes the issue?

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 32d3d36..bfd6c45 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -6418,7 +6418,8 @@ static bool HasSameValue(const SCEV *A, const SCEV *B) {
if (const SCEVUnknown *BU = dyn_cast(B))
if (const Instruction *AI = dyn_cast(AU->getValue()))
if (const Instruction *BI = dyn_cast(BU->getValue()))

  •      if (AI->isIdenticalTo(BI) && !AI->mayReadFromMemory())

  •      if (AI->isIdenticalTo(BI) && !AI->mayReadFromMemory() &&

  •          !isa<AllocaInst>(AI))
       return true;

    // Otherwise assume they may have a different value.

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llvmbot commented Sep 27, 2015

Yes, this patch does solve the problem.
Thanks for looking into this!

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sanjoy commented Sep 27, 2015

Should be fixed in r248690

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llvmbot commented Sep 27, 2015

Confirmed, r248690 fixes the problem.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
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