<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/71052>71052</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Call site info: Missing DW_AT_call_value opportunity - spilled value stack slot not used
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          OCHyams
      </td>
    </tr>
</table>

<pre>
    clang version 18.0.0 (bc41b0a)
Target: x86_64-unknown-linux-gnu

There is no `DW_AT_call_site_parameter` entry for the call to `f1` in this reproducer:
```
float f1(float p1);
float fun(float *f) {
  float v = *f;
  return f1(v) + v;
}
```
```
$ clang -O2 -g -c test.cpp -o - | llvm-dwarfdump - --name=fun --show-children
-:      file format elf64-x86-64

0x00000027: DW_TAG_subprogram
              DW_AT_name        ("fun")
 ...

0x00000037:   DW_TAG_formal_parameter
 ...

0x00000040:   DW_TAG_variable
 ...

0x00000049:   DW_TAG_call_site
 DW_AT_call_origin      (0x00000050)
 DW_AT_call_return_pc   (0x0000000000000010)

0x0000004f: NULL
```
```
$ clang -O2 -g -c test.cpp -o - | llvm-objdump -d -
Disassembly of section .text:

0000000000000000 <_Z3funPf>:
 0: 50                           pushq %rax
       1: f3 0f 10 07 movss (%rdi), %xmm0           # xmm0 = mem[0],zero,zero,zero
 5: f3 0f 11 44 24 04            movss %xmm0, 0x4(%rsp)        # spill xmm0
       b: e8 00 00 00 00               callq 0x10 <_Z3funPf+0x10>
 10: f3 0f 58 44 24 04            addss 0x4(%rsp), %xmm0
      16: 58 popq  %rax
      17: c3 retq
```

It looks like currently only loads and copies are interpreted to build `DW_AT_call_value` expressions.

If a parameter register value has been spilled to the stack before the call, I believe we should be able to use the spilled value in the `DW_AT_call_value` expression.

I think we should/could have a `DW_AT_call_site_parameter` DIE like this for this reproducer:
```
DW_TAG_call_site_parameter
 DW_AT_location   (DW_OP_reg<XMM0>)
   DW_AT_call_value (DW_OP_breg<RSP>+4, DW_OP_deref_size, 0x4)
```

Here's the optimized IR to reproduce the issue with `llc`:
```
; ModuleID = 'test.cpp'
source_filename = "test.cpp"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

; Function Attrs: mustprogress uwtable
define dso_local noundef float @_Z3funPf(ptr nocapture noundef readonly %f) local_unnamed_addr #0 !dbg !10 {
entry:
  call void @llvm.dbg.value(metadata ptr %f, metadata !16, metadata !DIExpression()), !dbg !18
  %0 = load float, ptr %f, align 4, !dbg !19, !tbaa !20
  call void @llvm.dbg.value(metadata float %0, metadata !17, metadata !DIExpression()), !dbg !18
  %call = tail call noundef float @_Z2f1f(float noundef %0), !dbg !24
  %add = fadd float %0, %call, !dbg !25
  ret float %add, !dbg !26
}

declare !dbg !27 noundef float @_Z2f1f(float noundef) local_unnamed_addr #1

; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
declare void @llvm.dbg.value(metadata, metadata, metadata) #2

attributes #0 = { mustprogress uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #1 = { "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #2 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
!llvm.ident = !{!9}

!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 18.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "test.cpp", directory: "/")
!2 = !{i32 7, !"Dwarf Version", i32 5}
!3 = !{i32 2, !"Debug Info Version", i32 3}
!4 = !{i32 1, !"wchar_size", i32 4}
!5 = !{i32 8, !"PIC Level", i32 2}
!6 = !{i32 7, !"PIE Level", i32 2}
!7 = !{i32 7, !"uwtable", i32 2}
!8 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
!9 = !{!"clang version 18.0.0"}
!10 = distinct !DISubprogram(name: "fun", linkageName: "_Z3funPf", scope: !1, file: !1, line: 2, type: !11, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
!11 = !DISubroutineType(types: !12)
!12 = !{!13, !14}
!13 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
!14 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
!15 = !{!16, !17}
!16 = !DILocalVariable(name: "f", arg: 1, scope: !10, file: !1, line: 2, type: !14)
!17 = !DILocalVariable(name: "v", scope: !10, file: !1, line: 3, type: !13)
!18 = !DILocation(line: 0, scope: !10)
!19 = !DILocation(line: 3, column: 13, scope: !10)
!20 = !{!21, !21, i64 0}
!21 = !{!"float", !22, i64 0}
!22 = !{!"omnipotent char", !23, i64 0}
!23 = !{!"Simple C++ TBAA"}
!24 = !DILocation(line: 4, column: 10, scope: !10)
!25 = !DILocation(line: 4, column: 16, scope: !10)
!26 = !DILocation(line: 4, column: 3, scope: !10)
!27 = !DISubprogram(name: "f1", linkageName: "_Z2f1f", scope: !1, file: !1, line: 1, type: !28, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)
!28 = !DISubroutineType(types: !29)
!29 = !{!13, !13}
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzsWV9zozgS_zTkpYsUCLDxQx4Se7KbuvlXO7O7V_fiEiBs7QiJkYTj7Ke_agkwOE4yU7eP50rZAvU_tbp_3VKoMXwnGbsJsrsg21zRzu6Vvvm0_vWJNuaqUNXTTSmo3MGBacOVhDi_jq4jCEhelGlcRDQgqyDaBNHtV6p3zAbJLRzzxXaRhp38JtWjDAWX3THcyc7T9dR7phlwA1JBsIg2f25vv25LKsTWcMu2LdW0YZbpYBEBk1Y_Qa002D0DJALruOoYp7kEu-cGNGu1qrqS6SDptQSLqP9zj7VQ1EIdByT3wzZG85O72XQnx_mA3NYBWUGw7EkA_MQBgmTjp5NxSjPbaenlHxwbuYPDSBAsNxetOn8kKXifh58IhDsIS7DM2OuybSFUEEKwXIMQhyasHqmuq65pIYQwlLRhQbKpOwlhaPbqMSz3XFSaSS84dG5Z1VwwdGZDLTBRL9LwmC_CRTrdnegYuQ9Z4n5u_tx-vf1la7qi1WqnaTMsePrxO-hsiFYByQNCnCfJGCBwfX19SUnilMCgxpkmJhHwKnMazZgPVHNaCPYG02rGNIZdzzUJRqX5jku_ooE7i05LmpD63d-25Zx6-MQnrjNjajTm4-_v3__D0aGKv3xsVBB65g031BjWFOIJVA2GlRZz-tqyoz3ljLfu7ANBst7-J6k7-bkOkncjNTj_ZxG8_Gk7s_8OAck0Pc4iJ0bWOoGohjiCaAmNOhgDLngyXXF0GFkj57FpphoCkoB7hUnYsCbI7qIg2wRk_TfT6uzHa8wmumJIUyApROnUzEG5U4Z6o2Pam2JazOaJctNyIZwJswUVqITlEEWnv_kHI-U7RMd47lByh6_Qr15cHJ3MzfKL5tKqMubcxom7pobFC7dJObSq_Q4XtiJ2KVgmCGHfL8ed-36wIJT6ZkDwbwzKTmsmLQaTFE8gFK0MUFlBqVrODFBEeGmZbjWzrELQLjouqjPAP1DRMYfzx1Yzg2XGzNL2oQYKIx6AZjtucOAYYU8NFIxJvyleDdYJY2n5DQpWK83GwoEOeoCCCc4ODB4ZmL3qRAUFA4QN5O2MJx_EeS2uyLC3LZ8bjoVJfjvpCch96fTt6YEBfbPybR7eeVe7Aucr4A9VunNkewanXq1QJXUQgEGRb_7cfvq81WwXJOt_f_jg4nFEOoDzhZ9YCs_z25fPjuUuRTf7qYppVm8N_5uNKbV6JcB-ZZoFZGmcs1VrecP_ZhU8_IY7My7bzXJjOgaP3O7RjUKUKOoFdwTJHXxQVSfYw6av3MsBNQOy9ERGdbpkW6yPWMZ6OnKiI57OukYHKmqpoE-qswMlC5sguWVhS5ZoSULcFz7G80ccLVL3FfJxEJM8SG5jkod1HvUj6V4tBvZFGn6JXW2dmWI1b8Vo8Ivt18B18sl9J30JuLVWG8SApjPWVXlmDHSP9lRMK1ZzyaAyyoWNAKk6WbG674iCNDrBWd5aDVKVtLWdZiOlZrRyUBGQzPVVTtC2k-jvakurSiO8YnsZV8UOfxAoh-bL9YGnyuM7wYPiFSrHknddFbtrn5Qkb5iluEeAtniFaxhfoujF-ZvNw7sxkR2srkZMHe3JB-0ByXwBQtzzTkDSqTYq-E5CeiZhkGgL6rSS6CcXNPSmWfRsScv_dUnOBFyVpVx4gy7sM6njemySh3lv0Jlwkk6E06pysmsczFfRqz5jziat9YmBVtUZ3eK8w-4jthRYgyaEyx9dzcvRGb-dRBj5QhRYf6SqNcMMME-ydMIfuazAtKzsBHXpBY9ciP7s0LBG6aeA5FJJNkLlsJA3Q2O6-_MxHkaSWf5TazUvOstMn3OIHsu7iwiAsNJwGQq2oyI8sNIqHT7yyu4RVJJNQEgUEIJkUoVW07blchc2dEJgNZrqaFxpDlutrJdUdHXNdOirRE-e97Qe4sKy7cap_rwym68ZRagxI1FA7spGHQKyxtEx94P6aLQfNc3RD4xh44D40TFfDtI7yWa6d0wyzUs3PUTb3JPx6Mn_e4MkZPTGP5cUcJbnAYnHjCi7vgzGWDZIHJ1oe6rG9QHXtaA7M6clPaok_e8A3Fn_u-h_l_1v_kw2r5i0c6Gr58b6XKu4sVyW1qP0WjUtF-x3yW1AcjzgdXTH-tP3-9uPv2zX21Z0xn9507BTQQrEcFd6Tk0h7talixsXCmvg5tPQWyGxD8Y16E5a3rA_PAvOOGxmDXf1419cOvL7TogNK7odTppWcOueHqTgksudO7pQ4QIJEDu_4oYOzB-nwIaWD-7aPNzjekg-NGD9Mqb9F1lDxbVLk6d-OiD300sG3MbJBvCEwLBdASGbR6prGNbX-yIhkE13MjnjJxN-XCc8yFpdEJJMhaRnQuKTkMdyT_V2SO-eOZ0yZ2fM-Yn588Ma3rMDExNeMuVdvLz6zw_vXuddvsw7tIIvcOYvc1bos5DLWoX-urFh0iIqlt8wWHqBsQ_CicjVPI9eCegJ08Xc-nK6uCL5JLKG-6k1CC6_0R37eJo79bKOwJSqneXaee4JLt2zo7ZPJ-J4ZH8_JXHw49L74V7Q3WetrEK2yt3f-Je3QqypEGbDTKl5wSqfb_cn1i-f8WGDnTl3LYhn9q9PKU7W0CGweJNcTmtmKZes-qgqZgZbs1liTjLzS1do1Vku2VdcGsnR1JFtln2z9MPnAU3jWYifsmzzcEcNL3vB0-3xLbX3P2ZLcguJe2KyVFWPNO5U-m7bE0_sSE8KNkzzA6sG2-lucqvZKndFsXV7RtZQUOMX2S8umapfpDMV2dlShwIRL2dLXZwseY9F8I_hknK-3H6pVDvz4mdhF_1U3M0tXf6QCYdL0f6q2uRcbTJTm8_VWn8IGZijS7om3KtXuZ3qUomucZWq36gXpZHorNgPiOwHfJHCrFcg8TP8mQYkUpDLjOQZo2okb5XF3gCxfyIiuSwieSbiC2_wiI_9WEDu4Ovd7e0Z9JH0VXelZ-56w_kk-ylpizekLX5G2ls7uZwB02Voj19Bdn_e-zlcj88CneSvovgLSD2B5Ml68h8EWn92H9lWLwFt8vw_TVfVTVKtkhW9YjfxYpWvyDJZkav9TRXHyyrLI5qxJM7oKosySpIkSuPVIl6V6RW_IRFJ4jjClFgk5Lqo6owuaZTlyWqVJ2mQRqyhXFy7Dljp3ZW7mbtZxlFGrgQtmDDu_4uESPbor-3Q-9nmSt-4f1QU3c7gqZYba05SLLeC3WABBMMtA-wg0BEfsBmVu-fXkaptlbZY6J4gPLu-9ZfBRig84FvoDKuuOi1u9ta26F7XRd7vuN13xXWpmoDcoyH9Dx7O_mKlDci9M98E5N4t778BAAD__9oPKV8">