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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [Win64][cygming] calling @__main is mis-assumed not to clobber registers (esp. rax, rcx, rdx)"
href="http://llvm.org/bugs/show_bug.cgi?id=17023">17023</a>
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<th>Summary</th>
<td>[Win64][cygming] calling @__main is mis-assumed not to clobber registers (esp. rax, rcx, rdx)
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>geek4civic@gmail.com
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>@__main is inserted in @main for targeting cygming, also on x86_64
; %c is passed via %rcx.
define i32 @main(i32 %c, i8** nocapture readnone %v) nounwind readnone {
; tail call void asm sideeffect "nop",
"r,~{rcx},~{dirflag},~{fpsr},~{flags}"(i32 %c) nounwind
%cmp = icmp eq i32 %c, 2
%cond = select i1 %cmp, i32 2, i32 0
ret i32 %cond
}
$ llc -mtriple=x86_64-mingw32
; w/o asm
main:
pushq %rbp
movq %rsp, %rbp
callq __main
cmpl $2, %ecx ; XXX might be clobbered in __main!
; w/asm (uncomment the line)
main: # @main
# BB#0:
pushq %rbp
movq %rsp, %rbp
movl %ecx, %eax
callq __main ; XXX it must clobber %rax!
#APP
nop
#NO_APP
cmpl $2, %eax
We should teach, in X86DAGToDAGISel::EmitSpecialCodeForMain(),
that __main should be treated as same as generic CC_X86_Win64_C.
IMO, we could consider that clang might be responsible to insert @__main,
instead of llvm codegen.</pre>
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