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[AMD Public Use]<br>
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The incoming direction also looks totally broken:</div>
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define void @test_byval(i8* byval(i8) %ptr) {
<div> %load = load volatile i8, i8* %ptr</div>
<div> ret void</div>
<div>}</div>
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// SDAG: <br>
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<div>.cfi_startproc</div>
<div>ldrb w8, [sp]</div>
ret</blockquote>
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// GISel:</div>
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<blockquote style="margin-top:0;margin-bottom:0">.cfi_startproc
<div>; %bb.0:</div>
<div>ldr x8, [sp]</div>
<div>ldrb wzr, [x8]</div>
<div>ret<br>
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<div>I have a patch which fixes this second half, but wanted to confirm this is fixing the AArch64 ABI and not breaking it</div>
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<div>-Matt<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> on behalf of Arsenault, Matthew via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Sent:</b> Friday, March 5, 2021 8:57 PM<br>
<b>To:</b> llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> [llvm-dev] Are calls with byval broken for AArch64 GlobalISel?</font>
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[AMD Public Use]<br>
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<div>[CAUTION: External Email]
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[AMD Public Use]<br>
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<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
I noticed the byval handling is largely missing from the GlobalISel call lowering implementation, and noticed AArch64 is producing different code vs. SelectionDAG. Specifically, it is not copying byval argument contents and is just directly passing the pointer.
If the callee were to modify the memory, it would incorrectly overwrite the caller's value.<br>
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Consider this minimal example:</div>
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define i32 @call_byval(i32 %arg0) {
<div> %alloca = alloca i32</div>
<div> %ret = call i32 @callee(i32* byval %alloca)</div>
<div> ret i32 %ret</div>
}</div>
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For SelectionDAG, this inserts a copy:</div>
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<blockquote style="margin-top:0; margin-bottom:0">sub sp, sp, #32
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<div>str x30, [sp, #16]<br>
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<div>.cfi_def_cfa_offset 32</div>
<div>.cfi_offset w30, -16</div>
<div>ldr w8, [sp, #28] // Read value<br>
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<div>str w8, [sp] // Copy to outgoing slot<br>
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bl callee</blockquote>
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For GlobalISel, this copy is missing:</div>
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<blockquote style="margin-top:0; margin-bottom:0">sub sp, sp, #32<br>
<div>str x30, [sp, #16]<br>
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<div>.cfi_def_cfa_offset 32</div>
<div>.cfi_offset w30, -16</div>
bl callee<br>
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-Matt<br>
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