[dwarf] make dwarf fission compatible with RISCV relaxations 2/2

[dlav-sc]

This patch makes DWARF fission compatible with RISC-V relaxations by using indirect addressing for the DW_AT_high_pc attribute. This eliminates the remaining relocations in .dwo files.

[llvmbot]

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-backend-risc-v

Author: None (dlav-sc)

Changes

This patch makes DWARF fission compatible with RISC-V relaxations by using indirect addressing for the DW_AT_high_pc attribute. This eliminates the remaining relocations in .dwo files.

---

Full diff: https://github.com/llvm/llvm-project/pull/164813.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp (+5-3)
• (modified) llvm/test/DebugInfo/RISCV/relax_dwo_ranges.ll (+30-14)

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 518121e200190..12ad5c18e9600 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -493,10 +493,12 @@ void DwarfCompileUnit::attachLowHighPC(DIE &D, const MCSymbol *Begin,
   assert(End->isDefined() && "Invalid end label");
 
   addLabelAddress(D, dwarf::DW_AT_low_pc, Begin);
-  if (DD->getDwarfVersion() < 4)
-    addLabelAddress(D, dwarf::DW_AT_high_pc, End);
-  else
+  if (DD->getDwarfVersion() >= 4 &&
+      (!isDwoUnit() || !llvm::isRangeRelaxable(Begin, End))) {
     addLabelDelta(D, dwarf::DW_AT_high_pc, End, Begin);
+    return;
+  }
+  addLabelAddress(D, dwarf::DW_AT_high_pc, End);
 }
 
 // Add info for Wasm-global-based relocation.
diff --git a/llvm/test/DebugInfo/RISCV/relax_dwo_ranges.ll b/llvm/test/DebugInfo/RISCV/relax_dwo_ranges.ll
index f8ab7fc5ad900..64f83ba1a7d7f 100644
--- a/llvm/test/DebugInfo/RISCV/relax_dwo_ranges.ll
+++ b/llvm/test/DebugInfo/RISCV/relax_dwo_ranges.ll
@@ -1,12 +1,13 @@
 ; 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: FileCheck --input-file=%t.txt %s --check-prefix=RELOCS --allow-empty --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:
+; RUN: FileCheck --input-file=%t.txt %s --check-prefix=RELOCS --allow-empty --implicit-check-not=warning:
+; RUN: llvm-objdump -h %t | FileCheck --check-prefix=HDR %s
 
 ; In the RISC-V architecture, the .text section is subject to
 ; relaxation, meaning the start address of each function can change
@@ -49,60 +50,75 @@
 
 ; clang -g -S -gsplit-dwarf --target=riscv64 -march=rv64gc -O0 relax_dwo_ranges.cpp
 
-; Currently, square() still uses an offset to represent the function's end address,
-; which requires a relocation here.
-; RELOCS: warning: unexpected relocations for dwo section '.debug_info.dwo'
+; RELOCS-NOT: warning: unexpected relocations for dwo section '.debug_info.dwo'
 
+; Make sure we don't produce any relocations in any .dwo section
+; HDR-NOT: .rela.{{.*}}.dwo
+
+; Ensure that 'square()' function uses indexed start and end addresses
 ; DWARF5: .debug_info.dwo contents:
 ; DWARF5: DW_TAG_subprogram
-; DWARF5-NEXT: DW_AT_low_pc [DW_FORM_addrx]    (indexed (00000000) address = 0x0000000000000000 ".text")
-; DWARF5-NEXT: DW_AT_high_pc [DW_FORM_data4] (0x00000000)
+; DWARF5-NEXT: DW_AT_low_pc  [DW_FORM_addrx]    (indexed (00000000) address = 0x0000000000000000 ".text")
+; DWARF5-NEXT: DW_AT_high_pc [DW_FORM_addrx]    (indexed (00000001) address = 0x0000000000000044 ".text")
 ; DWARF5: DW_AT_name {{.*}} "square") 
 ; DWARF5: DW_TAG_formal_parameter
 
+; HDR-NOT: .rela.{{.*}}.dwo
+
 ; Ensure there is no unnecessary addresses in .o file
 ; DWARF5: .debug_addr contents:
 ; DWARF5: Addrs: [
 ; DWARF5-NEXT: 0x0000000000000000
+; DWARF5-NEXT: 0x0000000000000044
 ; DWARF5-NEXT: 0x0000000000000046
 ; DWARF5-NEXT: 0x000000000000006c
 ; DWARF5-NEXT: 0x00000000000000b0
 ; DWARF5-NEXT: ]
 
+; HDR-NOT: .rela.{{.*}}.dwo
+
 ; Ensure that 'boo()' and 'main()' use DW_RLE_startx_length and DW_RLE_startx_endx
 ; entries respectively
 ; DWARF5: .debug_rnglists.dwo contents:
 ; DWARF5: ranges:
-; DWARF5-NEXT: 0x00000014: [DW_RLE_startx_length]:  0x0000000000000001, 0x0000000000000024 => [0x0000000000000046, 0x000000000000006a)
+; DWARF5-NEXT: 0x00000014: [DW_RLE_startx_length]:  0x0000000000000002, 0x0000000000000024 => [0x0000000000000046, 0x000000000000006a)
 ; DWARF5-NEXT: 0x00000017: [DW_RLE_end_of_list  ]
-; DWARF5-NEXT: 0x00000018: [DW_RLE_startx_endx  ]:  0x0000000000000002, 0x0000000000000003 => [0x000000000000006c, 0x00000000000000b0)
+; DWARF5-NEXT: 0x00000018: [DW_RLE_startx_endx  ]:  0x0000000000000003, 0x0000000000000004 => [0x000000000000006c, 0x00000000000000b0)
 ; DWARF5-NEXT: 0x0000001b: [DW_RLE_end_of_list  ]
 ; DWARF5-EMPTY:
 
+; HDR-NOT: .rela.{{.*}}.dwo
+
 ; DWARF4: .debug_info.dwo contents:
 ; DWARF4: DW_TAG_subprogram
-; DWARF4-NEXT: DW_AT_low_pc [DW_FORM_GNU_addr_index]	(indexed (00000000) address = 0x0000000000000000 ".text")
-; DWARF4-NEXT: DW_AT_high_pc [DW_FORM_data4]	(0x00000000)
+; DWARF4-NEXT: DW_AT_low_pc  [DW_FORM_GNU_addr_index]	(indexed (00000000) address = 0x0000000000000000 ".text")
+; DWARF4-NEXT: DW_AT_high_pc [DW_FORM_GNU_addr_index] (indexed (00000001) address = 0x0000000000000044 ".text")
 ; DWARF4: DW_AT_name {{.*}} "square") 
 
 ; DWARF4: DW_TAG_subprogram
-; DWARF4-NEXT: DW_AT_low_pc [DW_FORM_GNU_addr_index]	(indexed (00000001) address = 0x0000000000000046 ".text")
+; DWARF4-NEXT: DW_AT_low_pc [DW_FORM_GNU_addr_index]	(indexed (00000002) address = 0x0000000000000046 ".text")
 ; DWARF4-NEXT: DW_AT_high_pc [DW_FORM_data4]	(0x00000024)
 ; DWARF4: DW_AT_name {{.*}} "boo") 
 
 ; DWARF4: DW_TAG_subprogram
-; DWARF4-NEXT: DW_AT_low_pc [DW_FORM_GNU_addr_index]	(indexed (00000002) address = 0x000000000000006c ".text")
-; DWARF4-NEXT: DW_AT_high_pc [DW_FORM_data4]	(0x00000000)
+; DWARF4-NEXT: DW_AT_low_pc  [DW_FORM_GNU_addr_index] (indexed (00000003) address = 0x000000000000006c ".text")
+; DWARF4-NEXT: DW_AT_high_pc [DW_FORM_GNU_addr_index] (indexed (00000004) address = 0x00000000000000b0 ".text")
 ; DWARF4: DW_AT_name {{.*}} "main") 
 
+; HDR-NOT: .rela.{{.*}}.dwo
+
 ; Ensure there is no unnecessary addresses in .o file
 ; DWARF4: .debug_addr contents:
 ; DWARF4: Addrs: [
 ; DWARF4-NEXT: 0x0000000000000000
+; DWARF4-NEXT: 0x0000000000000044
 ; DWARF4-NEXT: 0x0000000000000046
 ; DWARF4-NEXT: 0x000000000000006c
+; DWARF4-NEXT: 0x00000000000000b0
 ; DWARF4-NEXT: ]
 
+; HDR-NOT: .rela.{{.*}}.dwo
+
 ; Function Attrs: mustprogress noinline optnone
 define dso_local noundef signext i32 @_Z6squarei(i32 noundef signext %0) #0 !dbg !11 {
   %2 = alloca i32, align 4

[asb]

#56642 is the relevant issue we have open on this. I'd be interested in any thoughts from @MaskRay and/or @dwblaikie

[dwblaikie]

Why allow-empty?

[dwblaikie]

For -NOT checks I'd try to keep the text matching as vague as possible, so the check is less likely to bit-rot if someone changes the wording and then the thing regresses.

like maybe RELOCS-NOT: warning:?