[LCSSA] Don't use VH callbacks to invalidate SCEV when creating LCSSA phis

In general ValueHandleBase::ValueIsRAUWd shouldn't be called when not
all uses of the value were actually replaced, though, currently
formLCSSAForInstructions calls it when it inserts LCSSA-phis.

Calls of ValueHandleBase::ValueIsRAUWd were added to LCSSA specifically
to update/invalidate SCEV. In the best case these calls duplicate some
of the work already done by SE->forgetValue, though in case when SCEV of
the value is SCEVUnknown, SCEV replaces the underlying value of
SCEVUnknown with the new value (i.e. acts like LCSSA-phi actually fully
replaces the value it is created for), which leads to SCEV being
corrupted because LCSSA-phi rarely dominates all uses of its inputs.

Fixes bug https://bugs.llvm.org/show_bug.cgi?id=44058.

Reviewers: fhahn, efriedma, reames, sanjoy.google

Reviewed By: fhahn

Subscribers: hiraditya, javed.absar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70593

1 files changed, 37 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LCSSA/pr44058.ll b/llvm/test/Transforms/LCSSA/pr44058.ll
new file mode 100644
index 00000000000..b6fa92ab7cb
--- /dev/null
+++ b/llvm/test/Transforms/LCSSA/pr44058.ll
@@ -0,0 +1,37 @@
+; RUN: opt -passes="verify<scalar-evolution>,lcssa,verify<scalar-evolution>" -verify-scev-strict -S %s
+
+; The first SCEV verification is required because it queries SCEV and populates
+; SCEV caches. Second SCEV verification checks if the caches are in valid state.
+
+; Check that the second SCEV verification doesn't fail.
+define void @foo(i32* %arg, i32* %arg1, i1 %arg2) {
+bb:
+  br label %bb3
+
+bb3:                                              ; preds = %bb13, %bb
+  %tmp = load i32, i32* %arg
+  %tmp4 = load i32, i32* %arg1
+  %tmp5 = add i32 %tmp4, %tmp
+  %tmp6 = icmp sgt i32 %tmp5, %tmp
+  br i1 %tmp6, label %bb7, label %bb11
+
+bb7:                                              ; preds = %bb3
+  br i1 %arg2, label %bb10, label %bb8
+
+bb8:                                              ; preds = %bb7
+  %tmp9 = add nsw i32 %tmp, 1
+  ret void
+
+bb10:                                             ; preds = %bb7
+  br label %bb11
+
+bb11:                                             ; preds = %bb10, %bb3
+  %tmp12 = phi i32 [ 0, %bb3 ], [ %tmp4, %bb10 ]
+  br label %bb13
+
+bb13:                                             ; preds = %bb13, %bb11
+  %tmp14 = phi i32 [ %tmp15, %bb13 ], [ 0, %bb11 ]
+  %tmp15 = add nuw nsw i32 %tmp14, 1
+  %tmp16 = icmp slt i32 %tmp15, %tmp12
+  br i1 %tmp16, label %bb13, label %bb3
+}