[llvm] DAG: Fix latent verifier error in statepoint lowering (PR #222894)

[Kazu Hirata via llvm-commits]

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@@ -0,0 +1,89 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -early-live-intervals < %s | FileCheck %s
+
+; A gc.relocate of a directly-lowered value (a constant or an alloca)
+; in an invoke's landing pad must rematerialize the value at the
+; relocate, not export a vreg defined after the statepoint call in the
+; invoke block.
+
+target triple = "x86_64-pc-linux-gnu"
+
+declare void @foo()
+
+define ptr addrspace(1) @relocate_constant_in_landing_pad() gc "statepoint-example" personality ptr null {
+; CHECK-LABEL: relocate_constant_in_landing_pad:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:  .Ltmp0: # EH_LABEL
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    xorl %edi, %edi
+; CHECK-NEXT:    callq *%rax
+; CHECK-NEXT:  .Ltmp3:
+; CHECK-NEXT:  .Ltmp1: # EH_LABEL
+; CHECK-NEXT:  # %bb.1: # %common.ret
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    popq %rcx
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+; CHECK-NEXT:  .LBB0_2: # %exceptional_return
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:  .Ltmp2: # EH_LABEL
+; CHECK-NEXT:    movl $1, %eax
+; CHECK-NEXT:    popq %rcx
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+entry:
+  %c = inttoptr i64 1 to ptr addrspace(1)
----------------
kazutakahirata wrote:

May I suggest another test just like this, but with `undef` instead of `1` (`%c = inttoptr i64 undef to ptr addrspace(1)`)?

With the current patch, it fails `-verify-machineinstrs` right after ISel:
```text
*** Bad machine code: Reading virtual register without a def ***
- function:    relocate_undef_in_landing_pad
- basic block: %bb.2 exceptional_return
- instruction: $rax = COPY %4:gr64
- operand 1:   %4:gr64
```
Because `SDV.isUndef()` is `true` in `LowerAsSTATEPOINT`, `Record.RematLeaf` is skipped and `ExportFromCurrentBlock(V)` is no longer called, so `getValue(DerivedPtr)` in `visitGCRelocate` allocates `%4:gr64` with no definition in `entry`.

https://github.com/llvm/llvm-project/pull/222894