[llvm] [FunctionAttrs] Add the "initializes" attribute inference (PR #97373)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `arc-builder` running on `arc-worker` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/7865

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: CodeGen/X86/ms-x86-intrinsics.c' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 1: /buildbot/worker/arc-folder/build/bin/clang -cc1 -internal-isystem /buildbot/worker/arc-folder/build/lib/clang/20/include -nostdsysteminc -Werror -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00          -triple i686--windows -Oz -emit-llvm /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c -o -          | /buildbot/worker/arc-folder/build/bin/FileCheck /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c -check-prefix=CHECK -check-prefix=CHECK-I386
+ /buildbot/worker/arc-folder/build/bin/clang -cc1 -internal-isystem /buildbot/worker/arc-folder/build/lib/clang/20/include -nostdsysteminc -Werror -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 -triple i686--windows -Oz -emit-llvm /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c -o -
+ /buildbot/worker/arc-folder/build/bin/FileCheck /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c -check-prefix=CHECK -check-prefix=CHECK-I386
RUN: at line 4: /buildbot/worker/arc-folder/build/bin/clang -cc1 -internal-isystem /buildbot/worker/arc-folder/build/lib/clang/20/include -nostdsysteminc -Werror -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00          -triple x86_64--windows -Oz -emit-llvm /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c -o -          | /buildbot/worker/arc-folder/build/bin/FileCheck /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c --check-prefix=CHECK --check-prefix=CHECK-X64
+ /buildbot/worker/arc-folder/build/bin/clang -cc1 -internal-isystem /buildbot/worker/arc-folder/build/lib/clang/20/include -nostdsysteminc -Werror -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 -triple x86_64--windows -Oz -emit-llvm /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c -o -
+ /buildbot/worker/arc-folder/build/bin/FileCheck /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c --check-prefix=CHECK --check-prefix=CHECK-X64
/buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c:174:21: error: CHECK-X64-LABEL: expected string not found in input
// CHECK-X64-LABEL: define dso_local i64 @test_mul128(i64 noundef %Multiplier, i64 noundef %Multiplicand, ptr{{[a-z_ ]*}}%HighProduct)
                    ^
<stdin>:118:83: note: scanning from here
define dso_local range(i64 0, -1) i64 @test__umulh(i64 noundef %a, i64 noundef %b) local_unnamed_addr #0 {
                                                                                  ^
<stdin>:129:1: note: possible intended match here
define dso_local i64 @test_mul128(i64 noundef %Multiplier, i64 noundef %Multiplicand, ptr nocapture noundef writeonly initializes((0, 8)) %HighProduct) local_unnamed_addr #3 {
^

Input file: <stdin>
Check file: /buildbot/worker/arc-folder/llvm-project/clang/test/CodeGen/X86/ms-x86-intrinsics.c

-dump-input=help explains the following input dump.

Input was:
<<<<<<
             .
             .
             .
           113:  %4 = trunc nuw i128 %3 to i64 
           114:  ret i64 %4 
           115: } 
           116:  
           117: ; Function Attrs: minsize mustprogress nofree norecurse nosync nounwind optsize willreturn memory(none) 
           118: define dso_local range(i64 0, -1) i64 @test__umulh(i64 noundef %a, i64 noundef %b) local_unnamed_addr #0 { 
label:174'0                                                                                       X~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
           119: entry: 
label:174'0     ~~~~~~~
           120:  %0 = zext i64 %a to i128 
label:174'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~
           121:  %1 = zext i64 %b to i128 
label:174'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~
           122:  %2 = mul nuw i128 %1, %0 
label:174'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~
           123:  %3 = lshr i128 %2, 64 
label:174'0     ~~~~~~~~~~~~~~~~~~~~~~~
           124:  %4 = trunc nuw i128 %3 to i64 
label:174'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...

```

</details>

https://github.com/llvm/llvm-project/pull/97373