Bug#948482: ppc64el patch improvement

[Frédéric Bonnard]

Package: src:qd
Version: 2.3.22+dfsg.1-3
Control: tags -1 patch ftbfs

--

Hi,

after contacting the ppc64 toolchain team about bug #935289, especially
Pat Haugen, he said :
---
Basically the testcase is sensitive to
precision differences when FMA instructions are used (floating point
multiply-add). The compiler will generate these insns when it sees
expressions of the form (a * b) + c. If you want to continue to compile the
code at -O2 you'll need to specify the compiler option "-ffp-contract=off"
in order to prevent the FMA transformation(s).
this is just something specific to the values being used in the
testcase. The compiler will continue to generate 'fmadd' type instructions
at -O2 unless -ffp-contract=off is specified. My digging into the testcase
showed that different results were produced based on whether a fmadd insn
was generated for a specific expression. If it was not the result was 0, if
it was the result was some very small value. That value is then used
further and differences compounded, as you could guess.
---

so, so we may improve the patch by changing -fno-tree-pre into -ffp-contract=off

Thanks,

F.
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