[llvm-branch-commits] [llvm] [AMDGPU] Fix DomTree preservation in SILowerControlFlow when nodes are deleted (PR #176691)

[Vikram Hegde via llvm-branch-commits]

https://github.com/vikramRH created https://github.com/llvm/llvm-project/pull/176691

None

>From 5572170b8098f2b67f589feffa447a419ce61198 Mon Sep 17 00:00:00 2001
From: vikhegde <vikram.hegde at amd.com>
Date: Fri, 16 Jan 2026 14:34:55 +0530
Subject: [PATCH] [AMDGPU] Fix DomTree preservation in SILowerControlFlow when
 nodes are deleted

---
 llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp |  5 ++
 ...i-lower-control-flow-preserve-dom-tree.mir | 59 +++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 llvm/test/CodeGen/AMDGPU/si-lower-control-flow-preserve-dom-tree.mir

diff --git a/llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp b/llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp
index bb912be85de74..9cc86e84407b1 100644
--- a/llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp
+++ b/llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp
@@ -744,6 +744,11 @@ bool SILowerControlFlow::removeMBBifRedundant(MachineBasicBlock &MBB) {
   if (PDT)
     PDT->applyUpdates(DTUpdates);
 
+  if (MDT && MDT->getNode(&MBB))
+    MDT->eraseNode(&MBB);
+  if (PDT && PDT->getNode(&MBB))
+    PDT->eraseNode(&MBB);
+
   MBB.clear();
   MBB.eraseFromParent();
   if (FallThrough && !FallThrough->isLayoutSuccessor(Succ)) {
diff --git a/llvm/test/CodeGen/AMDGPU/si-lower-control-flow-preserve-dom-tree.mir b/llvm/test/CodeGen/AMDGPU/si-lower-control-flow-preserve-dom-tree.mir
new file mode 100644
index 0000000000000..0760bdfee43d7
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/si-lower-control-flow-preserve-dom-tree.mir
@@ -0,0 +1,59 @@
+# RUN: llc -o /dev/null -mcpu=gfx1201 -mtriple=amdgcn-amd-amdhsa -passes="require<machine-post-dom-tree>,si-lower-control-flow,print<machine-post-dom-tree>" %s 2>&1 | FileCheck %s
+
+# CHECK: Inorder PostDominator Tree: 
+# CHECK-NEXT:   [1]  <<exit node>> {4294967295,4294967295} [0]
+# CHECK-NEXT:     [2] %bb.4 {4294967295,4294967295} [1]
+# CHECK-NEXT:       [3] %bb.2 {4294967295,4294967295} [2]
+# CHECK-NEXT:       [3] %bb.0 {4294967295,4294967295} [2]
+# CHECK-NEXT:       [3] %bb.1 {4294967295,4294967295} [2]
+
+---
+name:            preserve_dom_tree
+body:             |
+  bb.0.entry:
+    successors: %bb.1(0x40000000), %bb.4(0x40000000)
+    liveins: $vgpr0, $sgpr0_sgpr1, $ttmp9
+  
+    %6:sreg_32 = COPY $ttmp9
+    %5:sgpr_64(p4) = COPY killed $sgpr0_sgpr1
+    %4:vgpr_32(s32) = COPY killed $vgpr0
+    %0:sgpr_128 = S_LOAD_DWORDX4_IMM %5(p4), 0, 0
+    %7:sreg_32_xm0_xexec = S_LOAD_DWORD_IMM killed %5(p4), 28, 0
+    %10:sreg_64_xexec_xnull = REG_SEQUENCE %0.sub2, %subreg.sub0, %0.sub3, %subreg.sub1
+    %12:sreg_32 = S_AND_B32 killed %7, 65535, implicit-def dead $scc
+    %39:vreg_64 = REG_SEQUENCE killed %4(s32), %subreg.sub0, undef %40:vgpr_32, %subreg.sub1
+    %16:vreg_64, $sgpr_null = V_MAD_U64_U32_e64 killed %6, killed %12, killed %39, 0, implicit $exec
+    %20:vgpr_32 = GLOBAL_LOAD_UBYTE_SADDR killed %10, killed %16.sub0, 0, 0, implicit $exec
+    %21:vgpr_32 = V_AND_B32_e64 1, killed %20, implicit $exec
+    %22:sreg_32 = V_CMP_EQ_U32_e64 1, killed %21, implicit $exec
+    %1:sreg_32 = SI_IF killed %22, %bb.4, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+    S_BRANCH %bb.1
+  
+  bb.1:
+    successors: %bb.2(0x40000000), %bb.3(0x40000000)
+  
+    %23:sreg_32 = COPY $exec_lo
+    %25:vgpr_32 = V_MBCNT_LO_U32_B32_e64 %23, 0, implicit $exec
+    %26:sreg_32 = V_CMP_EQ_U32_e64 0, killed %25, implicit $exec
+    %3:sreg_32 = SI_IF killed %26, %bb.3, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+    S_BRANCH %bb.2
+  
+  bb.2:
+    successors: %bb.3(0x80000000)
+  
+    %27:sreg_32 = S_BCNT1_I32_B32 killed %23, implicit-def dead $scc
+    %28:vgpr_32 = V_CVT_F32_UBYTE0_e64 killed %27, 0, 0, implicit $exec
+    %38:vgpr_32 = nofpexcept V_MUL_F32_e64 0, 1092616192, 0, killed %28, 0, 0, implicit $mode, implicit $exec
+    %34:sreg_64_xexec_xnull = REG_SEQUENCE killed %0.sub0, %subreg.sub0, %0.sub1, %subreg.sub1
+    %35:vgpr_32 = V_MOV_B32_e32 0, implicit $exec
+    GLOBAL_ATOMIC_ADD_F32_SADDR killed %35, killed %38, killed %34, 0, 0, implicit $exec
+  
+  bb.3:
+    successors: %bb.4(0x80000000)
+  
+    SI_END_CF killed %3, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+  
+  bb.4:
+    SI_END_CF killed %1, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+    S_ENDPGM 0
+...