[llvm] [Peephole] Check instructions from CopyMIs are still COPY (PR #69511)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: None (weiguozhi)

<details>
<summary>Changes</summary>

Function foldRedundantCopy records COPY instructions in CopyMIs and uses it later. But other optimizations may delete or modify it. So before using it we should check if the extracted instruction is existing and still a COPY instruction.

---
Full diff: https://github.com/llvm/llvm-project/pull/69511.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/PeepholeOptimizer.cpp (+3-1) 
- (added) llvm/test/CodeGen/X86/peephole-copy.ll (+20) 


``````````diff
diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index f413ca5b04f48cf..09ae2680f5516ba 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -1445,7 +1445,9 @@ bool PeepholeOptimizer::foldRedundantCopy(
   }
 
   MachineInstr *PrevCopy = CopyMIs.find(SrcPair)->second;
-  if (!LocalMIs.count(PrevCopy))
+  // A COPY instruction can be deleted or changed by other optimizations.
+  // Check if the previous COPY instruction is existing and still a COPY.
+  if (!LocalMIs.count(PrevCopy) || !PrevCopy->isCopy())
     return false;
 
   assert(SrcSubReg == PrevCopy->getOperand(1).getSubReg() &&
diff --git a/llvm/test/CodeGen/X86/peephole-copy.ll b/llvm/test/CodeGen/X86/peephole-copy.ll
new file mode 100644
index 000000000000000..60f25a3bc7feee4
--- /dev/null
+++ b/llvm/test/CodeGen/X86/peephole-copy.ll
@@ -0,0 +1,20 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 3
+; RUN: llc < %s -mtriple=i686-- | FileCheck %s
+
+; In peephole optimization the modified COPY instruction should not cause
+; compiler failure.
+
+define dso_local void @c() {
+; CHECK-LABEL: c:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movl $512, %eax # imm = 0x200
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    retl
+entry:
+  tail call void asm sideeffect "", "q,~{dirflag},~{fpsr},~{flags}"(i32 512)
+  tail call void asm sideeffect "", "q,~{dirflag},~{fpsr},~{flags}"(i32 512)
+  ret void
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/69511