[llvm-branch-commits] [llvm] release/22.x: [ShrinkWrap] Ensure we do not crash on unreachable blocks. (#178009) (PR #178433)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport f5de33dbf59a30246a6113e507e0cb41c21b9e45

Requested by: @<!-- -->davemgreen

---
Full diff: https://github.com/llvm/llvm-project/pull/178433.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/ShrinkWrap.cpp (+5-1) 
- (added) llvm/test/CodeGen/AArch64/shrink-wrap-unreachable.ll (+36) 


``````````diff
diff --git a/llvm/lib/CodeGen/ShrinkWrap.cpp b/llvm/lib/CodeGen/ShrinkWrap.cpp
index d83bbc2c31b6d..37592489a10ba 100644
--- a/llvm/lib/CodeGen/ShrinkWrap.cpp
+++ b/llvm/lib/CodeGen/ShrinkWrap.cpp
@@ -784,7 +784,11 @@ void ShrinkWrapImpl::updateSaveRestorePoints(MachineBasicBlock &MBB,
       if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) {
         // Push Save outside of this loop if immediate dominator is different
         // from save block. If immediate dominator is not different, bail out.
-        Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
+        SmallVector<MachineBasicBlock *> Preds;
+        for (auto *PBB : Save->predecessors())
+          if (MDT->isReachableFromEntry(PBB))
+            Preds.push_back(PBB);
+        Save = FindIDom<>(*Save, Preds, *MDT);
         if (!Save)
           break;
       } else {
diff --git a/llvm/test/CodeGen/AArch64/shrink-wrap-unreachable.ll b/llvm/test/CodeGen/AArch64/shrink-wrap-unreachable.ll
new file mode 100644
index 0000000000000..414045591b691
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/shrink-wrap-unreachable.ll
@@ -0,0 +1,36 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -mtriple=aarch64-linux-gnu -o - %s | FileCheck %s
+
+; Ensure we do not crash on unreachable blocks.
+
+define void @func_44(i1 %tobool3.not, ptr %g_530) {
+; CHECK-LABEL: func_44:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mov x8, xzr
+; CHECK-NEXT:  .LBB0_1: // %for.cond2
+; CHECK-NEXT:    // =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    ldr wzr, [x8]
+; CHECK-NEXT:    b .LBB0_1
+entry:
+  br label %for.cond2.outer
+
+for.cond2.outer:                                  ; preds = %for.inc, %entry
+  %add23.ph = phi i8 [ 0, %for.inc ], [ 0, %entry ]
+  br label %for.cond2
+
+for.cond2:                                        ; preds = %cleanup12.split, %for.cond2, %for.cond2.outer
+  %load = load volatile i32, ptr null, align 4
+  br i1 %tobool3.not, label %if.end, label %for.cond2
+
+if.end:                                           ; preds = %for.cond2
+  %tobool7.not = icmp eq i64 0, 0
+  br i1 %tobool7.not, label %for.inc, label %cleanup12.split
+
+for.inc:                                          ; preds = %if.end
+  %add = or i8 %add23.ph, 0
+  br label %for.cond2.outer
+
+cleanup12.split:                                  ; preds = %if.end
+  store i64 0, ptr %g_530, align 8
+  br label %for.cond2
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/178433