[llvm] 0e1ffa3 - [SLP]Fix a crash when comparing phis from unreachable blocks

[Alexey Bataev via llvm-commits]

Author: Alexey Bataev
Date: 2025-02-18T08:20:48-08:00
New Revision: 0e1ffa397ef35fe55f7bd768d42f94241d1a2caa

URL: https://github.com/llvm/llvm-project/commit/0e1ffa397ef35fe55f7bd768d42f94241d1a2caa
DIFF: https://github.com/llvm/llvm-project/commit/0e1ffa397ef35fe55f7bd768d42f94241d1a2caa.diff

LOG: [SLP]Fix a crash when comparing phis from unreachable blocks

Need to check if the block is reachable before comparing phis from it to
avoid compiler crash when requesting node.

Fixes report in https://github.com/llvm/llvm-project/pull/110529#issuecomment-2664723338

Added: 
    llvm/test/Transforms/SLPVectorizer/AArch64/unreachable-blocks-with-phis.ll

Modified: 
    llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 703fc7e3f9fa2..f2aa0e8328585 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -5724,6 +5724,10 @@ BoUpSLP::getReorderingData(const TreeEntry &TE, bool TopToBottom) {
 
     auto CompareByBasicBlocks = [&](BasicBlock *BB1, BasicBlock *BB2) {
       assert(BB1 != BB2 && "Expected 
diff erent basic blocks.");
+      if (!DT->isReachableFromEntry(BB1))
+        return false;
+      if (!DT->isReachableFromEntry(BB2))
+        return true;
       auto *NodeA = DT->getNode(BB1);
       auto *NodeB = DT->getNode(BB2);
       assert(NodeA && "Should only process reachable instructions");

diff  --git a/llvm/test/Transforms/SLPVectorizer/AArch64/unreachable-blocks-with-phis.ll b/llvm/test/Transforms/SLPVectorizer/AArch64/unreachable-blocks-with-phis.ll
new file mode 100644
index 0000000000000..aeb82d800a2f7
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/AArch64/unreachable-blocks-with-phis.ll
@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S --passes=slp-vectorizer -mtriple=aarch64  < %s | FileCheck %s
+
+define void @test() {
+; CHECK-LABEL: define void @test() {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = load <2 x i32>, ptr null, align 1
+; CHECK-NEXT:    br label %[[IF_END:.*]]
+; CHECK:       [[IF_THEN:.*]]:
+; CHECK-NEXT:    br label %[[IF_END]]
+; CHECK:       [[IF_END]]:
+; CHECK-NEXT:    [[TMP1:%.*]] = phi <2 x i32> [ [[TMP0]], %[[ENTRY]] ], [ poison, %[[IF_THEN]] ]
+; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <2 x i32> [[TMP1]], i32 0
+; CHECK-NEXT:    store i32 [[TMP2]], ptr null, align 1
+; CHECK-NEXT:    br label %[[TRAP:.*]]
+; CHECK:       [[BB3:.*:]]
+; CHECK-NEXT:    [[TMP4:%.*]] = extractelement <2 x i32> [[TMP1]], i32 1
+; CHECK-NEXT:    store i32 [[TMP4]], ptr null, align 1
+; CHECK-NEXT:    ret void
+; CHECK:       [[TRAP]]:
+; CHECK-NEXT:    unreachable
+;
+entry:
+  %g_2197.real32.pre = load i32, ptr null, align 1
+  %g_2197.imag33.pre = load i32, ptr getelementptr inbounds nuw ({ i32, i32 }, ptr null, i32 0, i32 1), align 1
+  br label %if.end
+
+if.then:
+  br label %if.end
+
+if.end:
+  %g_2197.imag33 = phi i32 [ %g_2197.imag33.pre, %entry ], [ 0, %if.then ]
+  %g_2197.real32 = phi i32 [ %g_2197.real32.pre, %entry ], [ 0, %if.then ]
+  store i32 %g_2197.real32, ptr  null, align 1
+  br label %trap
+
+0:
+  store i32 %g_2197.imag33, ptr  null, align 1
+  ret void
+
+trap:
+  unreachable
+}