Re: Compiler stress tests?

Stephen Baynes <>
17 Jan 1997 23:24:13 -0500

          From comp.compilers

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Compiler stress tests? (1997-01-02)
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Re: Compiler stress tests? (Stephen Baynes) (1997-01-17)
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From: Stephen Baynes <>
Newsgroups: comp.compilers
Date: 17 Jan 1997 23:24:13 -0500
Organization: Compilers Central
References: 97-01-020 97-01-024 97-01-033
Keywords: testing

Clyde Smith-Stubbs ( wrote:

: It's quite frightening when you apply this kind of verification
: to an existing compiler - we find it's normal that the test suite
: has only been testing about 70% of the compiler! Of the balance,
: some turns out to be unreachable, much proves to be correct, but
: some is bound to be wrong.

It can be very difficult to find a case that will test some parts of
the compiler, yet it may be very difficult to prove that those parts
cannot be used in practice. I had a case where there were a number of
different special cases of register allocations that had to be allowed
for in some operations. I could not find code that would cause all of
them to happen, nor prove that the ones not tried would never come up.
I also found that small changes to the register allocation algorithms
would change which special cases the test cases came up with. So even
if one had a set of tests that had covered them all, they might not do
so in a later version. Testing this code at module level could be done
but would be very difficult. All one could do was throw as many
different examples as possible at the compiler and hope that it
covered all the cases that would come up in practice.

It is important to take your test data from as many sources as
possible as different sources will follow different patterns. A good
general rule of computing is each additional user will reveal a new
class of bugs (because they will do something different from everyone

Stephen Baynes MBCS CEng
Philips Semiconductors Ltd
Southampton SO15 0DJ +44 (01703) 316431
United Kingdom

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