[lld] [ELF][LTO] Add baseline test for invalid relocations against runtime calls (PR #127286)

[Fangrui Song via llvm-commits]

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+; REQUIRES: arm
+;; https://github.com/llvm/llvm-project/issues/127284
+;; Test for LTO optimizing out references to symbols that are pulled in by
+;; compiler-generated libcalls (post LTO).
+;; The problem here is that the call to __aeabi_ldivmod is generated post-LTO,
+;; during ISel, so aeabi_ldivmod.o is only marked as required afterwards but by
+;; that time we have decided that all the callees of __aeabi_ldivmod are not
+;; needed and have been marked as ABS zero symbols.
+; RUN: rm -rf %t && split-file %s %t && cd %t
+; RUN: llvm-as divmoddi4.ll -o divmoddi4.bc
+; RUN: llvm-mc -filetype=obj -triple=armv7-none-unknown-eabi aeabi_ldivmod.s -o aeabi_ldivmod.o
+;; With an explicit __aebi_ldivmod call in the input IR this works as expected:
+; RUN: llvm-as main-explicit.ll -o main-explicit-ldivmod.bc
+; RUN: ld.lld main-explicit-ldivmod.bc --start-lib aeabi_ldivmod.o divmoddi4.bc --end-lib -o test.exe -Bstatic
+; RUN: llvm-objdump -d -r -t test.exe | FileCheck %s --check-prefix=GOOD-DUMP
+; GOOD-DUMP-LABEL: SYMBOL TABLE:
+; GOOD-DUMP: [[#]] g     F .text	[[#]] _start
+; GOOD-DUMP: [[#]] g     F .text	00000024 __aeabi_ldivmod
+; GOOD-DUMP: [[#]] g     F .text	[[#]] __divmoddi4
+; GOOD-DUMP-LABEL: <__aeabi_ldivmod>:
+; GOOD-DUMP:       bl	0x20140 <__divmoddi4>   @ imm = #0x28
+
+; But if the call is generated by ISel, we end up with an invalid reference:
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MaskRay wrote:

`;; `

https://github.com/llvm/llvm-project/pull/127286