[PATCH] D51770: [IndVars] Set Changed when we delete dead instructions. PR38855

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: etherzhhb, uabelho, skatkov, sanjoy.

IndVars does not set `Changed` flag when it eliminates dead instructions. As result,
it may made IR modifications and report that it has done nothing. It leads to inconsistent
preservedanalyzes results.


https://reviews.llvm.org/D51770

Files:
  lib/Transforms/Scalar/IndVarSimplify.cpp
  test/Transforms/IndVarSimplify/pr38855.ll


Index: test/Transforms/IndVarSimplify/pr38855.ll
===================================================================
--- test/Transforms/IndVarSimplify/pr38855.ll
+++ test/Transforms/IndVarSimplify/pr38855.ll
@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -inline -functionattrs -indvars  < %s | FileCheck %s
+
+; Check that the invalidation happens correctly and the test does not crash.
+define void @f2() {
+; CHECK-LABEL: @f2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_COND:%.*]]
+; CHECK:       for.cond:
+; CHECK-NEXT:    br label [[FOR_COND]]
+;
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond, %entry
+  %a.0 = phi i32 [ 1, %entry ], [ 0, %for.cond ]
+  call void @f1(i32 %a.0)
+  br label %for.cond
+}
+
+define internal void @f1(i32 %p1) noinline {
+entry:
+  ret void
+}
Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -2490,8 +2490,10 @@
   // which are now dead.
   while (!DeadInsts.empty())
     if (Instruction *Inst =
-            dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
+            dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val())) {
+      Changed = true;
       RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
+    }
 
   // The Rewriter may not be used from this point on.
 


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