qcolombet · Apr 25, 2026
diff --git a/llvm/lib/CodeGen/MIRParser/MILexer.cpp b/llvm/lib/CodeGen/MIRParser/MILexer.cpp
@@ -295,6 +295,7 @@ static MIToken::TokenKind getIdentifierKind(StringRef Identifier) {
       .Case("call-frame-size", MIToken::kw_call_frame_size)
       .Case("noconvergent", MIToken::kw_noconvergent)
       .Case("mmra", MIToken::kw_mmra)
+      .Case("lr-split", MIToken::kw_lr_split)
       .Default(MIToken::Identifier);
 }
 

diff --git a/llvm/lib/CodeGen/MIRParser/MILexer.h b/llvm/lib/CodeGen/MIRParser/MILexer.h
@@ -148,6 +148,7 @@ struct MIToken {
     kw_call_frame_size,
     kw_noconvergent,
     kw_mmra,
+    kw_lr_split,
 
     // Metadata types.
     kw_distinct,

diff --git a/llvm/lib/CodeGen/MIRParser/MIParser.cpp b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
@@ -1535,7 +1535,8 @@ bool MIParser::parseInstruction(unsigned &OpCode, unsigned &Flags) {
          Token.is(MIToken::kw_disjoint) ||
          Token.is(MIToken::kw_nusw) ||
          Token.is(MIToken::kw_samesign) ||
-         Token.is(MIToken::kw_inbounds)) {
+         Token.is(MIToken::kw_inbounds) ||
+         Token.is(MIToken::kw_lr_split)) {
     // clang-format on
     // Mine frame and fast math flags
     if (Token.is(MIToken::kw_frame_setup))
@@ -1578,6 +1579,8 @@ bool MIParser::parseInstruction(unsigned &OpCode, unsigned &Flags) {
       Flags |= MachineInstr::SameSign;
     if (Token.is(MIToken::kw_inbounds))
       Flags |= MachineInstr::InBounds;
+    if (Token.is(MIToken::kw_lr_split))
+      Flags |= MachineInstr::LRSplit;
 
     lex();
   }

diff --git a/llvm/lib/CodeGen/MIRPrinter.cpp b/llvm/lib/CodeGen/MIRPrinter.cpp
@@ -899,6 +899,8 @@ static void printMI(raw_ostream &OS, MFPrintState &State,
     OS << "samesign ";
   if (MI.getFlag(MachineInstr::InBounds))
     OS << "inbounds ";
+  if (MI.getFlag(MachineInstr::LRSplit))
+    OS << "lr-split ";
 
   // NOTE: Please add new MIFlags also to the MI_FLAGS_STR in
   // llvm/utils/update_mir_test_checks.py.

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -1901,6 +1901,8 @@ void MachineInstr::print(raw_ostream &OS, ModuleSlotTracker &MST,
     OS << "samesign ";
   if (getFlag(MachineInstr::InBounds))
     OS << "inbounds ";
+  if (getFlag(MachineInstr::LRSplit))
+    OS << "lr-split ";
 
   // Print the opcode name.
   if (TII)

diff --git a/llvm/test/CodeGen/MIR/AMDGPU/lr-split-flag.mir b/llvm/test/CodeGen/MIR/AMDGPU/lr-split-flag.mir
@@ -0,0 +1,25 @@
+# RUN: llc -mtriple=amdgcn -mcpu=gfx950 -run-pass=none -o - %s | FileCheck %s
+#
+# Round-trip test for the 'lr-split' MIR text spelling of
+# MachineInstr::LRSplit. The flag is set by SplitKit on copies inserted for
+# live-range splitting; AMDGPU's SIInstrInfo::canAddToBBProlog uses it to
+# recognize WWM_COPY / IMPLICIT_DEF instructions as part of the BB prologue.
+
+---
+name: lr_split_roundtrip
+tracksRegLiveness: true
+machineFunctionInfo:
+  isEntryFunction: true
+registers:
+  - { id: 0, class: vgpr_32, flags: [ WWM_REG ] }
+  - { id: 1, class: vgpr_32, flags: [ WWM_REG ] }
+body: |
+  bb.0:
+    liveins: $vgpr0
+    %0:vgpr_32 = COPY $vgpr0
+    %1:vgpr_32 = lr-split WWM_COPY %0:vgpr_32
+    S_ENDPGM 0, implicit %1
+...
+
+# CHECK-LABEL: name: lr_split_roundtrip
+# CHECK: %1:vgpr_32 = lr-split WWM_COPY %0
diff --git a/llvm/utils/UpdateTestChecks/mir.py b/llvm/utils/UpdateTestChecks/mir.py
@@ -21,7 +21,7 @@
 MI_FLAGS_STR = (
     r"(frame-setup |frame-destroy |nnan |ninf |nsz |arcp |contract |afn "
     r"|reassoc |nuw |nsw |exact |nofpexcept |nomerge |unpredictable "
-    r"|noconvergent |nneg |disjoint |nusw |samesign |inbounds )*"
+    r"|noconvergent |nneg |disjoint |nusw |samesign |inbounds |lr-split )*"
 )
 VREG_DEF_FLAGS_STR = r"(?:dead |undef )*"