[llvm] [InstrRef] Preserve debug instr num in aarch64-cond-br-tuning. (PR #132081)

[Shubham Sandeep Rastogi via llvm-commits]

https://github.com/rastogishubham updated https://github.com/llvm/llvm-project/pull/132081

>From ad2652945a856ec20745ad1217e651722e48462f Mon Sep 17 00:00:00 2001
From: Shubham Sandeep Rastogi <srastogi22 at apple.com>
Date: Tue, 18 Mar 2025 13:57:22 -0700
Subject: [PATCH] [InstrRef] Preserve debug instr num in
 aarch64-cond-br-tuning.

The aarch64-cond-br-tuning pass transforms a CBZX instruction into a
conditional branch (B.cond). One of the by products of the
transformation is that the source instruction of the CBZX, which is an
ANDXri instruction, gets transformed into a ANDSXri instruction, however
this transformation doesn't preserve it's debug instruction number.

This patch fixes that issue.
---
 .../Target/AArch64/AArch64CondBrTuning.cpp    |  6 +++
 .../AArch64/cond-br-tuning-instr-ref.mir      | 54 +++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 llvm/test/CodeGen/AArch64/cond-br-tuning-instr-ref.mir

diff --git a/llvm/lib/Target/AArch64/AArch64CondBrTuning.cpp b/llvm/lib/Target/AArch64/AArch64CondBrTuning.cpp
index da72e35a248eb..a091ab45c7737 100644
--- a/llvm/lib/Target/AArch64/AArch64CondBrTuning.cpp
+++ b/llvm/lib/Target/AArch64/AArch64CondBrTuning.cpp
@@ -102,6 +102,12 @@ MachineInstr *AArch64CondBrTuning::convertToFlagSetting(MachineInstr &MI,
 
   MachineInstrBuilder MIB = BuildMI(*MI.getParent(), MI, MI.getDebugLoc(),
                                     TII->get(NewOpc), NewDestReg);
+
+  // If the MI has a debug instruction number, preserve that in the new Machine
+  // Instruction that is created.
+  if (MI.peekDebugInstrNum() != 0)
+    MIB->setDebugInstrNum(MI.peekDebugInstrNum());
+
   for (const MachineOperand &MO : llvm::drop_begin(MI.operands()))
     MIB.add(MO);
 
diff --git a/llvm/test/CodeGen/AArch64/cond-br-tuning-instr-ref.mir b/llvm/test/CodeGen/AArch64/cond-br-tuning-instr-ref.mir
new file mode 100644
index 0000000000000..589102ed63878
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/cond-br-tuning-instr-ref.mir
@@ -0,0 +1,54 @@
+# RUN: llc -mtriple=aarch64-unknown-linux-gnu -o - %s -run-pass=aarch64-cond-br-tuning | FileCheck %s
+
+# This testcase was obtained by looking at FileCheck.cpp and reducing it down via llvm-reduce
+
+# Check that the ANDXri preserves the debug info by retaining the debug-instr-number 1 in _ZN4llvmlsERNS_11raw_ostreamERKNS_5ErrorE after the aarch64-cond-br-tuning pass transforms it into a ANDSXri instruction.
+
+# CHECK: %{{[0-9]+}}:gpr64common = ANDSXri %{{[0-9]+}}, {{[0-9]+}}, implicit-def $nzcv, debug-instr-number 1
+# CHECK-NEXT: DBG_INSTR_REF !{{[0-9]+}}, !DIExpression(DW_OP_LLVM_arg, 0), dbg-instr-ref(1, 0)
+
+--- |
+  define ptr @_ZNK4llvm5Error6getPtrEv(ptr %this) local_unnamed_addr #0 {
+  entry:
+    %0 = ptrtoint ptr %this to i64
+    %and = and i64 %0, -2
+    %1 = inttoptr i64 %and to ptr
+    ret ptr %1
+  }
+  define noalias noundef ptr @_ZN4llvmlsERNS_11raw_ostreamERKNS_5ErrorE(ptr %E) local_unnamed_addr #1 !dbg !4 {
+  entry:
+    %0 = ptrtoint ptr %E to i64, !dbg !13
+    %and.i = and i64 %0, -2, !dbg !13
+    %tobool.not = icmp eq i64 %and.i, 0
+    br i1 %tobool.not, label %if.else, label %if.then
+  if.then:                                          ; preds = %entry
+    unreachable
+  if.else:                                          ; preds = %entry
+    ret ptr null
+  }
+  !llvm.module.flags = !{!0}
+  !llvm.dbg.cu = !{!1}
+  !0 = !{i32 2, !"Debug Info Version", i32 3}
+  !1 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !2, producer: "clang version 21.0.0git (\0A\0A\0Agit at github.com:llvm/llvm-project.git 6be6400848eeec027d0cca0662c105683bcc896b\0A\0A\0A)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !3, retainedTypes: !3, globals: !3, imports: !3, splitDebugInlining: false, nameTableKind: Apple, sysroot: "/Library/Developer/CommandLineTools/SDKs/MacOSX15.3.sdk", sdk: "MacOSX15.3.sdk")
+  !2 = !DIFile(filename: "/Users/shubhamrastogi/Development/llvm-project-instr-ref/llvm-project/llvm/lib/FileCheck/FileCheck.cpp", directory: "/Users/shubhamrastogi/Development/llvm-project-instr-ref/llvm-project/build-instr-ref-stage2", checksumkind: CSK_MD5, checksum: "ac1d2352ab68b965fe7993c780cf92d7")
+  !3 = !{}
+  !4 = distinct !DISubprogram(name: "operator<<", linkageName: "_ZN4llvmlsERNS_11raw_ostreamERKNS_5ErrorE", scope: !6, file: !5, line: 320, type: !7, scopeLine: 320, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !1, retainedNodes: !8)
+  !5 = !DIFile(filename: "llvm/include/llvm/Support/Error.h", directory: "/Users/shubhamrastogi/Development/llvm-project-instr-ref/llvm-project", checksumkind: CSK_MD5, checksum: "f166cdaeb719f8f71fbae8128cde93e4")
+  !6 = !DINamespace(name: "llvm", scope: null)
+  !7 = distinct !DISubroutineType(types: !3)
+  !8 = !{!9}
+  !9 = !DILocalVariable(name: "P", scope: !10, file: !5, line: 321, type: !11)
+  !10 = distinct !DILexicalBlock(scope: !4, file: !5, line: 321, column: 15)
+  !11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+  !12 = distinct !DICompositeType(tag: DW_TAG_class_type, name: "ErrorInfoBase", scope: !6, file: !5, line: 44, size: 64, flags: DIFlagTypePassByReference | DIFlagNonTrivial, elements: !3, vtableHolder: !12, identifier: "_ZTSN4llvm13ErrorInfoBaseE")
+  !13 = !DILocation(line: 321, column: 21, scope: !10)
+  !14 = !DILocation(line: 0, scope: !10)
+name:            _ZN4llvmlsERNS_11raw_ostreamERKNS_5ErrorE
+body:             |
+  bb.0.entry:
+    %1:gpr64 = COPY $x0
+    %2:gpr64common = ANDXri %1, 8190, debug-instr-number 1, debug-location !13
+    DBG_INSTR_REF !9, !DIExpression(DW_OP_LLVM_arg, 0), dbg-instr-ref(1, 0), debug-location !14
+    %0:gpr64sp = COPY %2, debug-location !13
+    CBZX %2, %bb.2
+  bb.2.if.else: