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<p class="MsoNormal">Hi Ramshankar,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">giving it a try:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">> The result from the AA-Evaluator prints this:<o:p></o:p></p>
<p class="MsoNormal">> NoAlias: i8** getelementptr inbounds ([4 x i8*], [4 x i8*]* @pc, i32 0, i32 0), i8*** @ppc<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">- the first is an 'i8**' (the address of pc), <o:p></o:p></p>
<p class="MsoNormal">- the second 'i8***' (aka the address of ppc.)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Those represent two different objects.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Greetings,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Jeroen Dobbelaere<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> <b>On Behalf Of
</b>ramshankar r via llvm-dev<br>
<b>Sent:</b> Tuesday, July 7, 2020 18:16<br>
<b>To:</b> llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Question about basic-aa's assumptions<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Any takers on this?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Best,<o:p></o:p></p>
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<p class="MsoNormal">Ram<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Mon, Jul 6, 2020 at 12:18 PM ramshankar r <<a href="mailto:ramshankar543@gmail.com">ramshankar543@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hi,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I have a test-case for which I seem to be getting incorrect information from basic-aa alias-analysis. Here it is:<o:p></o:p></p>
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<p class="MsoNormal">#include <stdio.h><br>
#define ARR_SIZE 4<br>
char c[ARR_SIZE];<br>
char *pc[ARR_SIZE];<br>
char **ppc = pc;<br>
<br>
int main() {<br>
<br>
pc[0] = &c[0];<br>
pc[1] = &c[1];<br>
pc[2] = &c[2];<br>
pc[3] = &c[3];<br>
<br>
printf(" ppc: %p\n"<br>
" pc : %p\n"<br>
" c : %p\n"<br>
" *pc: %p\n",<br>
ppc, pc, c, *pc);<br>
<br>
return 0;<br>
}<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The way I compiled it is as follows:<o:p></o:p></p>
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<p class="MsoNormal">clang -m32 -g pointer.c -emit-llvm -S -c<o:p></o:p></p>
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<p class="MsoNormal">opt pointer.ll -aa-pipeline=basic-aa -passes=aa-eval -print-all-alias-modref-info -disable-output
<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The result from the AA-Evaluator prints this:<o:p></o:p></p>
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<p class="MsoNormal"> NoAlias: i8** getelementptr inbounds ([4 x i8*], [4 x i8*]* @pc, i32 0, i32 0), i8*** @ppc<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">If we run the program, the result is this:<o:p></o:p></p>
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<p class="MsoNormal"> ppc: 0x565ee028<br>
pc : 0x565ee028<br>
c : 0x565ee024<br>
*pc: 0x565ee024<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Basically, I would have liked if basic-aa said ppc and pc are may-aliased to start with for this kind of usage. This is how the globals look like. The second one: "ppc" has "pc" on the right hand side.<o:p></o:p></p>
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<p class="MsoNormal"><br>
@pc = common dso_local global [4 x i8*] zeroinitializer, align 4, !dbg !0<br>
@ppc = dso_local global i8** getelementptr inbounds ([4 x i8*], [4 x i8*]* @pc, i32 0, i32 0), align 4, !dbg !6<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Best regards,<o:p></o:p></p>
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<p class="MsoNormal">Ram<o:p></o:p></p>
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