[PATCH] D99252: [LoopFlatten] Fix invalid assertion (PR49571)

[Ta-Wei Tu via Phabricator via llvm-commits]

TaWeiTu created this revision.
TaWeiTu added reviewers: SjoerdMeijer, fhahn.
Herald added a subscriber: hiraditya.
TaWeiTu requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

The `InductionPHI` is not necessarily the increment instruction, as
demonstrated in pr49571.ll.
This patch removes the assertion and instead bails out from the 
`LoopFlatten` pass if that happens.

This fixes https://bugs.llvm.org/show_bug.cgi?id=49571


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D99252

Files:
  llvm/lib/Transforms/Scalar/LoopFlatten.cpp
  llvm/test/Transforms/LoopFlatten/pr49571.ll


Index: llvm/test/Transforms/LoopFlatten/pr49571.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopFlatten/pr49571.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -S -loop-flatten -verify-loop-info -verify-dom-info -verify-scev -verify | FileCheck %s
+
+; CHECK-LABEL: @main
+
+define dso_local void @main() {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.end, %entry
+  br label %for.body
+
+for.body:                                         ; preds = %for.inc, %for.cond
+  %a.03 = phi i32 [ 0, %for.cond ], [ %inc, %for.inc ]
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body
+  %0 = add i32 %a.03, 1
+  %cmp = icmp slt i32 %0, 10
+  %inc = add nsw i32 %a.03, 1
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:                                          ; preds = %for.inc
+  br label %for.cond
+}
Index: llvm/lib/Transforms/Scalar/LoopFlatten.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopFlatten.cpp
+++ llvm/lib/Transforms/Scalar/LoopFlatten.cpp
@@ -176,8 +176,11 @@
   LLVM_DEBUG(dbgs() << "Found limit: "; Limit->dump());
 
   assert(InductionPHI->getNumIncomingValues() == 2);
-  assert(InductionPHI->getIncomingValueForBlock(Latch) == Increment &&
-         "PHI value is not increment inst");
+
+  if (InductionPHI->getIncomingValueForBlock(Latch) != Increment) {
+    LLVM_DEBUG(dbgs() << "PHI value is not increment inst");
+    return false;
+  }
 
   auto *CI = dyn_cast<ConstantInt>(
       InductionPHI->getIncomingValueForBlock(L->getLoopPreheader()));


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