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<p class="MsoNormal">Hi All,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Does anyone remember why clang rejects inline assembly where an input and output are tied together but are differently sized types? The code that rejects it (Sema::ActOnGCCAsmStmt()) is looking like it's intentional but it's not clear why
it does so.<o:p></o:p></p>
<p class="MsoNormal">My current theory is that it's to avoid dealing with cases where a register has to be tied to its own subregister or something along those lines.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Here's a trimmed version of the original failing case from the Linux Kernel:<o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">static __inline__ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> const struct in6_addr *daddr,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> __u32 len, unsigned short proto,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> __wsum sum)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">{<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> __asm__(<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> /* snip */<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> " addu %0, %5 # proto (long in network byte order)\n"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> " sltu $1, %0, %5 \n"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> /* snip */<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> " lw %1, 0(%2) # four words source address\n"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> /* snip */<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> : "=r" (sum), "=r" (proto)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> : "r" (saddr), "r" (daddr),<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> "0" (htonl(len)), "1" (htonl(proto)), "r" (sum));<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> return csum_fold(sum);<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">}<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Clang objects to the 'htonl(proto)' on the grounds that the type doesn't match 'proto':<o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">arch/mips/include/asm/checksum.h:285:27: error: unsupported inline asm: input with type '__be32' (aka 'unsigned int') matching output with type 'unsigned short'<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> "0" (htonl(len)), "1" (htonl(proto)), "r" (sum));<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> ^~~~~~~~~~~~<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="text-align:justify"><b><span style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#3333FF">Daniel Sanders<o:p></o:p></span></b></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#3333FF">Leading Software Design Engineer, MIPS Processor IP<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#3333FF">Imagination Technologies Limited<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify"><a href="http://www.imgtec.com/"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:blue">www.imgtec.com</span></a><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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