[PATCH] D130596: [StandardInstrumentations] Handle case where block order changes

[Arthur Eubanks via Phabricator via llvm-commits]

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Previously we'd go off the end of the BI iterator because we expected
that the relative positions of common blocks before and after were
consistent. That's not always true though, for example with
jump-threading.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D130596

Files:
  llvm/lib/Passes/StandardInstrumentations.cpp
  llvm/test/Other/ChangePrinters/print-changed-diff-block-ordering-changed.ll


Index: llvm/test/Other/ChangePrinters/print-changed-diff-block-ordering-changed.ll
===================================================================
--- /dev/null
+++ llvm/test/Other/ChangePrinters/print-changed-diff-block-ordering-changed.ll
@@ -0,0 +1,20 @@
+; RUN: opt -passes=jump-threading %s -disable-output --print-changed=diff 2>&1 | FileCheck %s
+
+; CHECK: IR Dump After JumpThreadingPass
+
+define void @f(i1 %0) {
+  br i1 %0, label %5, label %2
+
+2:                                                ; preds = %1
+  br i1 false, label %b, label %3
+
+3:                                                ; preds = %2
+  %4 = call i64 null()
+  br label %b
+
+b:                                                ; preds = %3, %2
+  br label %5
+
+5:                                                ; preds = %b, %1
+  ret void
+}
Index: llvm/lib/Passes/StandardInstrumentations.cpp
===================================================================
--- llvm/lib/Passes/StandardInstrumentations.cpp
+++ llvm/lib/Passes/StandardInstrumentations.cpp
@@ -612,7 +612,10 @@
     }
     // This section is in both; advance and print out any before-only
     // until we get to it.
-    while (*BI != *AI) {
+    // It's possible that this section has moved to be later than before. This
+    // will mess up printing most blocks side by side, but it's a rare case and
+    // it's better than crashing.
+    while (BI != BE && *BI != *AI) {
       HandlePotentiallyRemovedData(*BI);
       ++BI;
     }
@@ -622,7 +625,6 @@
     const T &AData = AFD.find(*AI)->getValue();
     const T &BData = BFD.find(*AI)->getValue();
     HandlePair(&BData, &AData);
-    ++BI;
     ++AI;
   }
 


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