[SPIR-V] Ensure that we don't have a dangling BlockAddress constants after internal intrinsic 'spv_switch' is processed

[VyacheslavLevytskyy]

After internal intrinsic 'spv_switch' is processed we need to delete G_BLOCK_ADDR instructions that were generated to keep track of the corresponding basic blocks. If we just delete G_BLOCK_ADDR instructions with BlockAddress operands, this leaves their BasicBlock counterparts in a "address taken" status. This would make AsmPrinter to generate a series of unneeded labels of a "Address of block that was removed by CodeGen" kind. This PR is to ensure that we don't have a dangling BlockAddress constants by zapping the BlockAddress nodes, and only after that proceed with erasing G_BLOCK_ADDR instructions.

See also #87823 for more details.

[llvmbot]

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

Author: Vyacheslav Levytskyy (VyacheslavLevytskyy)

Changes

After internal intrinsic 'spv_switch' is processed we need to delete G_BLOCK_ADDR instructions that were generated to keep track of the corresponding basic blocks. If we just delete G_BLOCK_ADDR instructions with BlockAddress operands, this leaves their BasicBlock counterparts in a "address taken" status. This would make AsmPrinter to generate a series of unneeded labels of a "Address of block that was removed by CodeGen" kind. This PR is to ensure that we don't have a dangling BlockAddress constants by zapping the BlockAddress nodes, and only after that proceed with erasing G_BLOCK_ADDR instructions.

---

Full diff: https://github.com/llvm/llvm-project/pull/92390.diff

2 Files Affected:

• (modified) llvm/lib/Target/SPIRV/SPIRVPreLegalizer.cpp (+18-1)
• (modified) llvm/test/CodeGen/SPIRV/branching/switch-range-check.ll (+3)

diff --git a/llvm/lib/Target/SPIRV/SPIRVPreLegalizer.cpp b/llvm/lib/Target/SPIRV/SPIRVPreLegalizer.cpp
index 6ee5d90d9afe1..9bff23dd96668 100644
--- a/llvm/lib/Target/SPIRV/SPIRVPreLegalizer.cpp
+++ b/llvm/lib/Target/SPIRV/SPIRVPreLegalizer.cpp
@@ -602,8 +602,25 @@ static void processSwitches(MachineFunction &MF, SPIRVGlobalRegistry *GR,
         ToEraseMI.insert(Next);
     }
   }
-  for (MachineInstr *BlockAddrI : ToEraseMI)
+
+  // If we just delete G_BLOCK_ADDR instructions with BlockAddress operands,
+  // this leaves their BasicBlock counterparts in a "address taken" status. This
+  // would make AsmPrinter to generate a series of unneeded labels of a "Address
+  // of block that was removed by CodeGen" kind. Let's first ensure that we
+  // don't have a dangling BlockAddress constants by zapping the BlockAddress
+  // nodes, and only after that proceed with erasing G_BLOCK_ADDR instructions.
+  Constant *Replacement =
+      ConstantInt::get(Type::getInt32Ty(MF.getFunction().getContext()), 1);
+  for (MachineInstr *BlockAddrI : ToEraseMI) {
+    if (BlockAddrI->getOpcode() == TargetOpcode::G_BLOCK_ADDR) {
+      BlockAddress *BA = const_cast<BlockAddress *>(
+          BlockAddrI->getOperand(1).getBlockAddress());
+      BA->replaceAllUsesWith(
+          ConstantExpr::getIntToPtr(Replacement, BA->getType()));
+      BA->destroyConstant();
+    }
     BlockAddrI->eraseFromParent();
+  }
 }
 
 static bool isImplicitFallthrough(MachineBasicBlock &MBB) {
diff --git a/llvm/test/CodeGen/SPIRV/branching/switch-range-check.ll b/llvm/test/CodeGen/SPIRV/branching/switch-range-check.ll
index 85a4d4db089cb..f8ce15323aacf 100644
--- a/llvm/test/CodeGen/SPIRV/branching/switch-range-check.ll
+++ b/llvm/test/CodeGen/SPIRV/branching/switch-range-check.ll
@@ -1,10 +1,13 @@
 ; RUN: llc -O0 -mtriple=spirv32-unknown-unknown %s -o - | FileCheck %s
 ; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv32-unknown-unknown %s -o - -filetype=obj | spirv-val %}
 
+; CHECK: OpFunction
 ; CHECK: %[[#Var:]] = OpPhi
 ; CHECK: OpSwitch %[[#Var]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]] [[#]] %[[#]]
 ; CHECK-COUNT-11: OpBranch
 ; CHECK-NOT: OpBranch
+; CHECK: OpReturn
+; CHECK-NEXT: OpFunctionEnd
 
 define spir_func void @foo(i64 noundef %addr, i64 noundef %as) {
 entry:

[Keenuts]

Thanks for fixing! 😊