[MCContext] Reverse order of DebugPrefixMap sort for generated assembly debug info

[dankm]

Summary

Match Clang's sorting, so that longer (more specific) prefix paths
will match before less specific paths.

[dankm]

I'm thinking about changing all the definitions of DebugPrefixMap like structures to just one named type, so that this is consistent everywhere.

[dankm]

Run clang-format

[dblaikie]

Test case?

[dankm]

In D132390#3740751, @dblaikie wrote:

Test case?

Hah. Just finished writing a basic test case. Incoming.

[dankm]

Updated debug-prefix-map.s test cases to detect this.

[MaskRay]

The test doesn't help. %t=... does not match the path component %t.foo. A nested directory is needed to test the situation.
You probably want to swap the order of the two -fdebug-prefix-map= for -dwarf-version=5 to get some variance.

[dankm]

In D132390#3741646, @MaskRay wrote:

The test doesn't help. %t=... does not match the path component %t.foo. A nested directory is needed to test the situation.

Sure it does. It's somewhat undocumented, and arguably a bug in its own right (I was torn when I implemented the original prefix mapping stuff), but it's a simple prefix substitution. /t=/lu turns /tmp into /lump happily.
In this case without the header change, that unit test turns the file path into /broken_root.foo/src.s.

You probably want to swap the order of the two -fdebug-prefix-map= for -dwarf-version=5 to get some variance.

I like this suggestion. The order of the parameters, so let's ensure that both work.

[dankm]

In D132390#3742950, @dankm wrote:

Sure it does. It's somewhat undocumented, and arguably a bug in its own right (I was torn when I implemented the original prefix mapping stuff), but it's a simple prefix substitution. /t=/lu turns /tmp into /lump happily.

Hmm. While this is true, it depends on how replace_path_prefix is called, and that seems inconsistent. That *is* a bug. Clang gives me multiple file names when I try that there. In llvm-mc, though it's always the string prefix.
I'll use subdirectories, since I now believe it *should* fail in the /t=/lu changing /tmp to /lump.

[dankm]

Use subdirectory rather than substring prefix matching in unit test.

[MaskRay]

llvm/test/MC/ELF/debug-prefix-map.s

2

mkdir -p %t.foo/bar

[raj.khem]

My local testing on clang-15 shows no problems with this patch so lgtm

[dankm]

llvm/test/MC/ELF/debug-prefix-map.s

2

I thought about that, but I also think doing it separately makes it more clear to readers that both paths will be used.

[MaskRay]

llvm/test/MC/ELF/debug-prefix-map.s

2

You may keep em, then it should still be clear

[dankm]

Attempt to fix the test case on Windows.

[dankm]

One more attemt to fix Windows tests before I actually install a
Windows VM to work on it..

[dankm]

Since I don't have commit access, can one of you commit this for me, please?

Assuming you're happy with the test updates.

[dankm]

Is it possible to get this into 15? Or do we need to wait for 16 at this point?

llvm/include/llvm/MC/MCContext.h

193–194

What happened to the const qualifier here?

[MaskRay]

llvm/include/llvm/MC/MCContext.h

193–194

const key is very uncommon and constness usually doesn't matter (value_type adds const to the key type anyway).

[MaskRay]

In D132390#3757111, @dankm wrote:

Is it possible to get this into 15? Or do we need to wait for 16 at this point?

I've created https://github.com/llvm/llvm-project/issues/57437 for 15.0.0 backport. If it is too late, we can request 15.0.1 backport.

[dankm]

In D132390#3757188, @MaskRay wrote:

I've created https://github.com/llvm/llvm-project/issues/57437 for 15.0.0 backport. If it is too late, we can request 15.0.1 backport.

Thanks!

llvm/include/llvm/MC/MCContext.h

193–194

Ah, missed that in the std::map spec. It makes sense that keys are always const, just didn't know it was guaranteed. Thanks.

llvm/include/llvm/MC/MCContext.h

private:
   /// catch errors if .secure_log_unique appears twice without
   /// .secure_log_reset appearing between them.
   bool SecureLogUsed = false;
 
   /// The compilation directory to use for DW_AT_comp_dir.
   SmallString<128> CompilationDir;
 
   /// Prefix replacement map for source file information.
-  std::map<const std::string, const std::string> DebugPrefixMap;
+  std::map<const std::string, const std::string, std::greater<std::string>>
+      DebugPrefixMap;
 
   /// The main file name if passed in explicitly.
   std::string MainFileName;
 
   /// The dwarf file and directory tables from the dwarf .file directive.
   /// We now emit a line table for each compile unit. To reduce the prologue
   /// size of each line table, the files and directories used by each compile
   /// unit are separated.

llvm/test/MC/ELF/debug-prefix-map.s

 # RUN: rm -rf %t.foo && mkdir %t.foo && cd %t.foo
 # RUN: cp %s %t.foo/src.s
 
 # RUN: llvm-mc -triple=x86_64 -g -dwarf-version=4 src.s -filetype=obj -o nomap.4.o
 # RUN: llvm-dwarfdump -v -debug-info -debug-line nomap.4.o | FileCheck --check-prefix=NO_MAP_V4 %s
 # RUN: llvm-mc -triple=x86_64 -g -dwarf-version=5 src.s -filetype=obj -o nomap.5.o
 # RUN: llvm-dwarfdump -v -debug-info -debug-line nomap.5.o | FileCheck --check-prefix=NO_MAP_V5 %s
 
 # RUN: llvm-mc -triple=x86_64 -g -dwarf-version=4 src.s -filetype=obj -o map.4.o -fdebug-prefix-map=%t.foo=src_root
 # RUN: llvm-dwarfdump -v -debug-info -debug-line map.4.o | FileCheck --check-prefix=MAP_V4 %s
 # RUN: llvm-mc -triple=x86_64 -g -dwarf-version=5 src.s -filetype=obj -o map.5.o -fdebug-prefix-map=%t.foo=src_root
 # RUN: llvm-dwarfdump -v -debug-info -debug-line map.5.o | FileCheck --check-prefix=MAP_V5 %s
 
-# RUN: llvm-mc -triple=x86_64 -g -dwarf-version=4 %t.foo/src.s -filetype=obj -o mapabs.4.o -fdebug-prefix-map=%t.foo=/src_root
+# RUN: llvm-mc -triple=x86_64 -g -dwarf-version=4 %t.foo/src.s -filetype=obj -o mapabs.4.o -fdebug-prefix-map=%t=/broken_root -fdebug-prefix-map=%t.foo=/src_root
 # RUN: llvm-dwarfdump -v -debug-info -debug-line mapabs.4.o | FileCheck --check-prefix=MAPABS_V4 %s
-# RUN: llvm-mc -triple=x86_64 -g -dwarf-version=5 %t.foo/src.s -filetype=obj -o mapabs.5.o -fdebug-prefix-map=%t.foo=/src_root
+# RUN: llvm-mc -triple=x86_64 -g -dwarf-version=5 %t.foo/src.s -filetype=obj -o mapabs.5.o -fdebug-prefix-map=%t=/broken_root -fdebug-prefix-map=%t.foo=/src_root
 # RUN: llvm-dwarfdump -v -debug-info -debug-line mapabs.5.o | FileCheck --check-prefix=MAPABS_V5 %s
 
 f:
   nop
 
 # NO_MAP_V4:      DW_AT_comp_dir [DW_FORM_string] ("{{.*}}.foo")
 # NO_MAP_V4:      file_names[  1]:
 # NO_MAP_V4-NEXT:   name: "src.s"