[llvm] [dwarf] make dwarf fission compatible with RISCV relaxations 1/2 (PR #166597)

[Fangrui Song via llvm-commits]

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+; RUN: llc -dwarf-version=5 -split-dwarf-file=foo.dwo -O0 %s -mtriple=riscv64-unknown-linux-gnu -filetype=obj -o %t
+; RUN: llvm-dwarfdump -v %t | FileCheck --check-prefix=DWARF5 %s
+; RUN: llvm-dwarfdump --debug-info %t 2> %t.txt
+; RUN: FileCheck --input-file=%t.txt %s --check-prefix=RELOCS --implicit-check-not=warning:
+
+; RUN: llc -dwarf-version=4 -split-dwarf-file=foo.dwo -O0 %s -mtriple=riscv64-unknown-linux-gnu -filetype=obj -o %t
+; RUN: llvm-dwarfdump -v %t | FileCheck --check-prefix=DWARF4 %s
+; RUN: llvm-dwarfdump --debug-info %t 2> %t.txt
+; RUN: FileCheck --input-file=%t.txt %s --check-prefix=RELOCS --implicit-check-not=warning:
+
+; In the RISC-V architecture, the .text section is subject to
+; relaxation, meaning the start address of each function can change
+; during the linking process. Therefore, the .debug_rnglists.dwo
+; section must obtain function's start addresses from the .debug_addr
+; section.
+
+; Generally, a function's body can be relaxed (for example, the
+; square() and main() functions in this test, which contain call
+; instructions). For such code ranges, the linker must place the
+; start and end addresses into the .debug_addr section and use
+; the DW_RLE_startx_endx entry form in the .debug_rnglists.dwo
+; section within the .dwo file.
+
+; However, some functions may not contain any relaxable instructions
+; (for example, the boo() function in this test). In these cases,
+; it is possible to use the more space-efficient DW_RLE_startx_length
+; range entry form.
+
+; From the code:
+
+; __attribute__((noinline)) int boo();
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MaskRay wrote:

https://llvm.org/docs/TestingGuide.html#elaborated-tests for tests requiring elaborate IR or assembly files where cleanup is less practical (e.g., a large amount of debug information output from Clang), you can include generation instructions within split-file part called gen. Then, run llvm/utils/update_test_body.py on the test file to generate the needed content.

https://github.com/llvm/llvm-project/pull/166597