[llvm] [StatepointLowering] Use Constant instead of TargetConstant for undef value (PR #81635)

[Danila Malyutin via llvm-commits]

https://github.com/danilaml created https://github.com/llvm/llvm-project/pull/81635

Prevents isel errors when trying to lower gc relocate of undef value (which turns into CopyToReg of TargetConstant). Such relocates may occur after DCE (e.g. after GVN removes some dead blocks) if there are not passes like instcombine scheduled after to clean them up.

Fixes #80294

>From ee3e8323af9dcd09eb4ab940ccdd76cb5762790e Mon Sep 17 00:00:00 2001
From: Danila Malyutin <dmalyutin at azul.com>
Date: Tue, 13 Feb 2024 19:02:16 +0400
Subject: [PATCH] [StatepointLowering] Use Constant instead of TargetConstant
 for undef value

Prevents isel errors when trying to lower gc relocate of undef value (which
turns into CopyToReg of TargetConstant). Such relocates may occur after DCE.

Fixes #80294
---
 .../SelectionDAG/StatepointLowering.cpp       |  2 +-
 .../CodeGen/X86/statepoint-relocate-undef.ll  | 32 +++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/X86/statepoint-relocate-undef.ll

diff --git a/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
index 1320479915e361..d7f4d1c8937563 100644
--- a/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
@@ -1287,7 +1287,7 @@ void SelectionDAGBuilder::visitGCRelocate(const GCRelocateInst &Relocate) {
   if (SD.isUndef() && SD.getValueType().getSizeInBits() <= 64) {
     // Lowering relocate(undef) as arbitrary constant. Current constant value
     // is chosen such that it's unlikely to be a valid pointer.
-    setValue(&Relocate, DAG.getTargetConstant(0xFEFEFEFE, SDLoc(SD), MVT::i64));
+    setValue(&Relocate, DAG.getConstant(0xFEFEFEFE, SDLoc(SD), MVT::i64));
     return;
   }
 
diff --git a/llvm/test/CodeGen/X86/statepoint-relocate-undef.ll b/llvm/test/CodeGen/X86/statepoint-relocate-undef.ll
new file mode 100644
index 00000000000000..5906398bcaf91c
--- /dev/null
+++ b/llvm/test/CodeGen/X86/statepoint-relocate-undef.ll
@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -verify-machineinstrs < %s | FileCheck %s
+
+target datalayout = "e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux-gnu"
+
+declare void @use(...)
+declare void @f()
+declare token @llvm.experimental.gc.statepoint.p0(i64, i32, ptr, i32, i32, ...)
+declare ptr addrspace(1) @llvm.experimental.gc.relocate.p1(token, i32, i32)
+
+;; Check that llvm doesn't crash if relcoate with undef base/derived ptr survives until isel
+define void @test_gcrelocate_undef(ptr addrspace(1) %ptr) gc "statepoint-example" {
+; CHECK-LABEL: test_gcrelocate_undef:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    movq %rdi, (%rsp)
+; CHECK-NEXT:    callq f at PLT
+; CHECK-NEXT:  .Ltmp0:
+; CHECK-NEXT:    movl $4278124286, %edi # imm = 0xFEFEFEFE
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    callq use at PLT
+; CHECK-NEXT:    popq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+  %tok = tail call token (i64, i32, ptr, i32, i32, ...)
+      @llvm.experimental.gc.statepoint.p0(i64 0, i32 0, ptr elementtype(void ()) @f, i32 0, i32 0, i32 0, i32 0) ["gc-live" (ptr addrspace(1) %ptr, ptr addrspace(1) undef), "deopt" (ptr addrspace(1) %ptr, i32 undef)]
+  %a = call ptr addrspace(1) @llvm.experimental.gc.relocate.p1(token %tok, i32 0, i32 1)
+  call void (...) @use(ptr addrspace(1) %a)
+  ret void
+}