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

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

Differential Revision: https://reviews.llvm.org/D51770
Reviewed By: skatkov

llvm-svn: 341633

2 files changed, 25 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 06836360610..80b7a42652a 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -2491,7 +2491,7 @@ bool IndVarSimplify::run(Loop *L) {
   while (!DeadInsts.empty())
     if (Instruction *Inst =
             dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
-      RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
+      Changed |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
 
   // The Rewriter may not be used from this point on.
 
diff --git a/llvm/test/Transforms/IndVarSimplify/pr38855.ll b/llvm/test/Transforms/IndVarSimplify/pr38855.ll
new file mode 100644
index 00000000000..b2d84e7abaf
--- /dev/null
+++ b/llvm/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
+}