[llvm-branch-commits] [llvm] d9f306a - [LV] Fix crash when generating remarks with multi-exit loops.

[Florian Hahn via llvm-branch-commits]

Author: Florian Hahn
Date: 2021-01-01T13:54:41Z
New Revision: d9f306aa52fe233a711af2d5baa0d6536f164b10

URL: https://github.com/llvm/llvm-project/commit/d9f306aa52fe233a711af2d5baa0d6536f164b10
DIFF: https://github.com/llvm/llvm-project/commit/d9f306aa52fe233a711af2d5baa0d6536f164b10.diff

LOG: [LV] Fix crash when generating remarks with multi-exit loops.

If DoExtraAnalysis is true (e.g. because remarks are enabled), we
continue with the analysis rather than exiting. Update code to
conditionally check if the ExitBB has phis or not a single predecessor.
Otherwise a nullptr is dereferenced with DoExtraAnalysis.

Added: 
    llvm/test/Transforms/LoopVectorize/remarks-multi-exit-loops.ll

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 65b3132dc3f1..3906b11ba4b9 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -1110,22 +1110,22 @@ bool LoopVectorizationLegality::canVectorizeLoopCFG(Loop *Lp,
       Result = false;
     else
       return false;
-  }
-
-  // The existing code assumes that LCSSA implies that phis are single entry
-  // (which was true when we had at most a single exiting edge from the latch).
-  // In general, there's nothing which prevents an LCSSA phi in exit block from
-  // having two or more values if there are multiple exiting edges leading to
-  // the exit block.  (TODO: implement general case)
-  if (!llvm::empty(ExitBB->phis()) && !ExitBB->getSinglePredecessor()) {
-    reportVectorizationFailure("The loop must have no live-out values if "
-                               "it has more than one exiting block",
-        "loop control flow is not understood by vectorizer",
-        "CFGNotUnderstood", ORE, TheLoop);
-    if (DoExtraAnalysis)
-      Result = false;
-    else
-      return false;
+  } else {
+    // The existing code assumes that LCSSA implies that phis are single entry
+    // (which was true when we had at most a single exiting edge from the latch).
+    // In general, there's nothing which prevents an LCSSA phi in exit block from
+    // having two or more values if there are multiple exiting edges leading to
+    // the exit block.  (TODO: implement general case)
+    if (!llvm::empty(ExitBB->phis()) && !ExitBB->getSinglePredecessor()) {
+      reportVectorizationFailure("The loop must have no live-out values if "
+                                 "it has more than one exiting block",
+          "loop control flow is not understood by vectorizer",
+          "CFGNotUnderstood", ORE, TheLoop);
+      if (DoExtraAnalysis)
+        Result = false;
+      else
+        return false;
+    }
   }
 
   return Result;

diff  --git a/llvm/test/Transforms/LoopVectorize/remarks-multi-exit-loops.ll b/llvm/test/Transforms/LoopVectorize/remarks-multi-exit-loops.ll
new file mode 100644
index 000000000000..7cbff7acc14b
--- /dev/null
+++ b/llvm/test/Transforms/LoopVectorize/remarks-multi-exit-loops.ll
@@ -0,0 +1,28 @@
+; RUN: opt -disable-output -loop-vectorize -pass-remarks-analysis='.*' -force-vector-width=2 2>&1 %s | FileCheck %s
+
+; Make sure LV does not crash when generating remarks for loops with non-unique
+; exit blocks.
+define i32 @test_non_unique_exit_blocks(i32* nocapture readonly align 4 dereferenceable(1024) %data, i32 %x) {
+; CHECK: loop not vectorized: loop control flow is not understood by vectorizer
+;
+entry:
+  br label %for.header
+
+for.header:                                         ; preds = %for.cond.lr.ph, %for.body
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %for.latch ]
+  %iv.next = add nuw nsw i64 %iv, 1
+  %exitcond.not = icmp eq i64 %iv.next, 256
+  br i1 %exitcond.not, label %header.exit, label %for.latch
+
+for.latch:
+  %arrayidx = getelementptr inbounds i32, i32* %data, i64 %iv
+  %lv = load i32, i32* %arrayidx, align 4
+  %cmp1 = icmp eq i32 %lv, %x
+  br i1 %cmp1, label %latch.exit, label %for.header
+
+header.exit:                       ; preds = %for.body
+  ret i32 0
+
+latch.exit:                       ; preds = %for.body
+  ret i32 %lv
+}