[Mips] Implement MipsInstrInfo::getNop() operation

[hpoussin]

Previously, this was calling TargetInstrInfo::getNop(), which contains:
llvm_unreachable("Not implemented");

Fixes #134913.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Hervé Poussineau (hpoussin)

Changes

Previously, this was calling TargetInstrInfo::getNop(), which contains:
llvm_unreachable("Not implemented");

Fixes #134913.

---

Full diff: https://github.com/llvm/llvm-project/pull/135524.diff

3 Files Affected:

• (added) clang/test/CodeGen/Mips/unreachable.cpp (+13)
• (modified) llvm/lib/Target/Mips/MipsInstrInfo.cpp (+7)
• (modified) llvm/lib/Target/Mips/MipsInstrInfo.h (+2)

diff --git a/clang/test/CodeGen/Mips/unreachable.cpp b/clang/test/CodeGen/Mips/unreachable.cpp
new file mode 100644
index 0000000000000..04fec8598088d
--- /dev/null
+++ b/clang/test/CodeGen/Mips/unreachable.cpp
@@ -0,0 +1,13 @@
+// REQUIRES: mips-registered-target
+// RUN: %clang_cc1 -triple mipsel-w64-windows-gnu -x c++ -mrelocation-model static -emit-obj %s -o - | llvm-objdump -a - | FileCheck %s
+// CHECK: file format coff-mips
+
+[[__noreturn__]] inline void g() {
+  __builtin_unreachable();
+}
+
+void f(int i)
+{
+  if (i == 0)
+    g();
+}
diff --git a/llvm/lib/Target/Mips/MipsInstrInfo.cpp b/llvm/lib/Target/Mips/MipsInstrInfo.cpp
index b81bb1186de72..0abe228b7547a 100644
--- a/llvm/lib/Target/Mips/MipsInstrInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsInstrInfo.cpp
@@ -87,6 +87,13 @@ MipsInstrInfo::GetMemOperand(MachineBasicBlock &MBB, int FI,
                                  MFI.getObjectAlign(FI));
 }
 
+MCInst MipsInstrInfo::getNop() const {
+  MCInst Nop;
+  // using Mips::NOP gives "fatal error: error in backend: Not supported instr: <MCInst 580>"
+  Nop.setOpcode(Mips::SSNOP);
+  return Nop;
+}
+
 //===----------------------------------------------------------------------===//
 // Branch Analysis
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Target/Mips/MipsInstrInfo.h b/llvm/lib/Target/Mips/MipsInstrInfo.h
index 06964c0161b4b..367f0ac5e8390 100644
--- a/llvm/lib/Target/Mips/MipsInstrInfo.h
+++ b/llvm/lib/Target/Mips/MipsInstrInfo.h
@@ -59,6 +59,8 @@ class MipsInstrInfo : public MipsGenInstrInfo {
 
   static const MipsInstrInfo *create(MipsSubtarget &STI);
 
+  MCInst getNop() const override;
+
   /// Branch Analysis
   bool analyzeBranch(MachineBasicBlock &MBB, MachineBasicBlock *&TBB,
                      MachineBasicBlock *&FBB,

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[brad0]

cc @MaskRay

[yingopq]

Did we need address this error and use Mips::NOP?
Mips::SSNOP is deprecated on MIPS32r6/MIPS64r6.

[hpoussin]

This patch is already an improvement, because it replaces a compiler crash by the use of a valid instruction (although deprecated in recent architectures).
However, you're right that it will be better to address this error and use Mips::NOP. Unfortunately, I think I won't be able to do it myself.

[MaskRay]

https://maskray.me/blog/2021-08-08-toolchain-testing#the-test-checks-too-little#the-test-checks-at-the-wrong-layer

Should generally avoid clang/test/CodeGen test for lib/Target changes. llvm/test/MC/Mips testing is in a pretty bad state. You might want to check RISCV/LoongArch.

(I will have limited internet access between April 20th and May 4th, and my response time may be delayed..)

[MaskRay]

clang++ -target "mipsel-w64-windows-gnu" -c test.cpp avoid deprecated -target . Use --target=