[AMDGPU] Improve crash message when S_WAITCNT_DEPCTR is missing its operand

[vporpo]

The code in the test is causing a crash in SIInstrInfo.cpp fixImplicitOperands() in MI.implicit_operands():

  for (auto &Op : MI.implicit_operands()) {

MachineInstr.h:

  mop_range implicit_operands() {
=>  return operands_impl().drop_front(getNumExplicitOperands());
  }

We are trying to drop 1 operand from the operands of MI which are 0.

By early returning we are no longer crashing at that point and we are getting a more meaningful error message:

*** Bad machine code: Too few operands ***
- function:    missing_operand_crash
- basic block: %bb.0  (0x5a9d30ced988)
- instruction: S_WAITCNT_DEPCTR
1 operands expected, but 0 given.

The code is still crashing at a different location, but at least we are getting an error message.

[llvmbot]

@llvm/pr-subscribers-backend-amdgpu

Author: vporpo (vporpo)

Changes

The code in the test is causing a crash in SIInstrInfo.cpp fixImplicitOperands() in MI.implicit_operands():

  for (auto &Op : MI.implicit_operands()) {

MachineInstr.h:

  mop_range implicit_operands() {
=>  return operands_impl().drop_front(getNumExplicitOperands());
  }

We are trying to drop 1 operand from the operands of MI which are 0.

By early returning we are no longer crashing at that point and we are getting a more meaningful error message:

*** Bad machine code: Too few operands ***
- function:    missing_operand_crash
- basic block: %bb.0  (0x5a9d30ced988)
- instruction: S_WAITCNT_DEPCTR
1 operands expected, but 0 given.

The code is still crashing at a different location, but at least we are getting an error message.

---

Full diff: https://github.com/llvm/llvm-project/pull/177065.diff

2 Files Affected:

• (modified) llvm/lib/Target/AMDGPU/SIInstrInfo.cpp (+3)
• (added) llvm/test/CodeGen/MIR/AMDGPU/s_wait_alu_missing_operand_crash.mir (+9)

diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index bd6c58d0f8945..96c16962b9d96 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -10001,6 +10001,9 @@ void SIInstrInfo::fixImplicitOperands(MachineInstr &MI) const {
   if (MI.isInlineAsm())
     return;
 
+  if (MI.getNumOperands() < MI.getNumExplicitOperands())
+    return;
+
   for (auto &Op : MI.implicit_operands()) {
     if (Op.isReg() && Op.getReg() == AMDGPU::VCC)
       Op.setReg(AMDGPU::VCC_LO);
diff --git a/llvm/test/CodeGen/MIR/AMDGPU/s_wait_alu_missing_operand_crash.mir b/llvm/test/CodeGen/MIR/AMDGPU/s_wait_alu_missing_operand_crash.mir
new file mode 100644
index 0000000000000..fd0f415ef8ef3
--- /dev/null
+++ b/llvm/test/CodeGen/MIR/AMDGPU/s_wait_alu_missing_operand_crash.mir
@@ -0,0 +1,9 @@
+# RUN: ! llc -mtriple=amdgcn -run-pass=none %s -o - 2>&1 | FileCheck %s
+
+---
+# CHECK: Bad machine code: Too few operands
+name: missing_operand_crash
+body: |
+  bb.0:
+    S_WAITCNT_DEPCTR
+...

[shiltian]

-o /dev/null

[vporpo]

done