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</o:shapelayout></xml><![endif]--></head><body lang=EN-IE link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>A little while ago I asked a question on CFE-Dev about a change in the behaviour of programs using the ISO C math functions, although that question should have been put to LLVM-Dev. But I got excellent clarification of the problem anyway. However, since then I have been trying to adapt our out-of-tree implementation to get the previous behaviour. The problem is that something like:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'>#include <math.h><o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'>extern double foo(double);<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'>int useMathName() {<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'> if ((exp(1.0) < 2.71) || (exp(1.0) > 2.72))<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'> return -1;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'> return 0;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'>}<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'>int useOtherName() {<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'> if ((foo(1.0) < 2.71) || (foo(1.0) > 2.72))<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'> return -1;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'> return 0;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-size:12.0pt;font-family:"Courier New"'>}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>With v3.8.0 the compiler elided both the calls to ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>exp</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ and the tests, so the function ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>useMathName</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ reduced to simply:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>return 0;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>But this was not correct as it ignored the possibility that the math functions could have the side-effect of changing ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New";color:black'>errno</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’, and this was fixed in v3.9.0, and the calls are no longer elided, though using the “as-if” rule, the tests are still eliminated and ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>useMathName</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ becomes:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>(void)exp(1.0);<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>(void)exp(1.0);<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>return 0;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>So I changed our implementation so that ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>-fno-math-errno</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ is the default for the tool-chain, and the ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New";color:black'>-fmath-errno</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ option is not passed on to the CC1 phase. I expected that this would allow the compiler to elide the calls, but it is not doing so. I don’t want to use ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>-ffast-math</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ as this has lots of FP issues, and I don’t want to make it the default.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>Any idea why the math functions are not elided? I am using ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>-O3</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ and implying ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>-fno-math-errno</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’. I have verified that our Toolchain implements ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>IsMathErrnoDefault</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ and returns ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>false</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’, and that the option ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>-fmath-errno</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’ is not being passed to the CC1 stage. Since our math function implementation does not in fact change ‘</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Courier New"'>errno</span><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>’, it is very desirable that this elision occurs in an FP safe way.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'> MartinO<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Book Antiqua",serif'><o:p> </o:p></span></p></div></body></html>