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<p class="MsoNormal"><span lang="EN-US">Hi all,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> I have a testcase whose result is different in O0 and O2 under llvm-4.0.0 version(trunk version also gets different result).
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> Test.c <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> ```<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US">#include<stdio.h><o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US">typedef int int128 __attribute__ ((vector_size (16)));<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:21.0pt"><span lang="EN-US">int main () {<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> long long int except = 0x1234567800000000;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> int err=0;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> long long a = 0x1234567812345678;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> int128 *b = (int128 *) &a;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> (*b)[0] = 0;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> if (a != except)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> err=1;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> if (err)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> printf("not equal\n");<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> else<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> printf("equal\n");<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> return 0;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US">}<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US">```<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US">O0 printed equal and O2 printed not equal. After some debugging, I found SROA pass changed the codes’ semantics. Here are IR during SROA<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US">```<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> %a = alloca i64, align 8<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> %0 = bitcast i64* %a to i8*<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> call void @llvm.lifetime.start(i64 8, i8* %0) #2<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> store i64 1311768465173141112, i64* %a, align 8, !tbaa !1<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> %1 = bitcast i64* %a to <4 x i32>*<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> %2 = load <4 x i32>, <4 x i32>* %1, align 16<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> %vecins = insertelement <4 x i32> %2, i32 0, i32 0<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> store <4 x i32> %vecins, <4 x i32>* %1, align 16<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> %3 = load i64, i64* %a, align 8, !tbaa !1<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> %cmp = icmp ne i64 %3, 1311768464867721216<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US"> br i1 %cmp, label %if.then, label %if.end<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US">```<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:10.5pt"><span lang="EN-US">But visitStoreInst will check whether Size(4 x i32 = 128) is greater than AllocaSize(64) and if so, mark the store inst(`store <4 x i32> %vecins, <4 x i32>* %1, align 16`) dead and delete it.
My intension is to change lower 32bits of b and store it back but the compiler thinks I will store all 128 bits. Is that a bug? Or if it’s test case problem, I think compiler can at least report some warnings in stdout(currently only reports warning in debug
log).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Ruobin<o:p></o:p></span></p>
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