[PATCH] D34616: [Reassociate] Make sure EraseInst sets MadeChange

[Mikael Holmén via Phabricator via llvm-commits]

uabelho created this revision.

EraseInst didn't report that it made IR changes through MadeChange.

It is essential that changes to the IR is reported correctly,
since for example ReassociatePass::run() will indicate that all
analyses are preserved otherwise.
And the CGPassManager determines if the CallGraph is up-to-date
based on status from InstructionCombiningPass::runOnFunction().


https://reviews.llvm.org/D34616

Files:
  lib/Transforms/Scalar/Reassociate.cpp
  test/Transforms/Reassociate/erase_inst_made_change.ll


Index: test/Transforms/Reassociate/erase_inst_made_change.ll
===================================================================
--- /dev/null
+++ test/Transforms/Reassociate/erase_inst_made_change.ll
@@ -0,0 +1,29 @@
+; RUN: opt < %s -inline -reassociate -S | FileCheck %s
+
+; This test case exposed a bug in reassociate where EraseInst's
+; removal a dead call wasn't recognized as changing the IR.
+; So when runOnFunction propagated the "made changes" upwards
+; to the CallGraphSCCPass it signalled that no changes had been
+; made, so CallGraphSCCPass assumed that the old CallGraph,
+; as known by that pass manager, still was up-to-date.
+;
+; This was detected as an assert when trying to remove the
+; no longer used function 'bar' (due to incorrect reference
+; count in the CallGraph).
+
+define void @foo() {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+entry:
+  call void @bar()
+  ret void
+}
+
+define internal void @bar() noinline nounwind readnone {
+; CHECK-NOT: bar
+entry:
+  ret void
+}
+
+
Index: lib/Transforms/Scalar/Reassociate.cpp
===================================================================
--- lib/Transforms/Scalar/Reassociate.cpp
+++ lib/Transforms/Scalar/Reassociate.cpp
@@ -1894,6 +1894,8 @@
         Op = Op->user_back();
       RedoInsts.insert(Op);
     }
+
+  MadeChange = true;
 }
 
 // Canonicalize expressions of the following form:


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