[PATCH] D79790: [ValueTracking] Fix crash in isGuaranteedNotToBeUndefOrPoison when V is in an unreachable block

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune created this revision.
aqjune added reviewers: spatel, nikic, lebedev.ri.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

This fixes PR45885 by fixing isGuaranteedNotToBeUndefOrPoison so it does not look into dominating
branch conditions of V when V is an instruction in an unreachable block.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D79790

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/DivRemPairs/pr45885.ll


Index: llvm/test/Transforms/DivRemPairs/pr45885.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/DivRemPairs/pr45885.ll
@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -div-rem-pairs -S -mtriple=aarch64-unknown-linux-gnu | FileCheck %s
+
+define void @g() {
+; CHECK-LABEL: @g(
+; CHECK-NEXT:  if.end:
+; CHECK-NEXT:    ret void
+; CHECK:       for.cond:
+; CHECK-NEXT:    [[TMP0:%.*]] = mul i16 [[DIV_I:%.*]], [[REM_FROZEN:%.*]]
+; CHECK-NEXT:    [[REM_DECOMPOSED:%.*]] = sub i16 1, [[TMP0]]
+; CHECK-NEXT:    [[REM_FROZEN]] = freeze i16 [[REM_DECOMPOSED]]
+; CHECK-NEXT:    [[DIV_I]] = sdiv i16 1, [[REM_FROZEN]]
+; CHECK-NEXT:    br label [[FOR_COND:%.*]]
+;
+if.end:
+  ret void
+
+for.cond:                                         ; preds = %for.cond
+  %rem = srem i16 1, %rem
+  %div.i = sdiv i16 1, %rem
+  br label %for.cond
+}
+
+
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -4821,12 +4821,17 @@
   if (!CtxI || !CtxI->getParent() || !DT)
     return false;
 
+  auto *DNode = DT->getNode(CtxI->getParent());
+  if (!DNode)
+    // Unreachable block
+    return false;
+
   // If V is used as a branch condition before reaching CtxI, V cannot be
   // undef or poison.
   //   br V, BB1, BB2
   // BB1:
   //   CtxI ; V cannot be undef or poison here
-  auto Dominator = DT->getNode(CtxI->getParent())->getIDom();
+  auto *Dominator = DNode->getIDom();
   while (Dominator) {
     auto *TI = Dominator->getBlock()->getTerminator();
 


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