[LoopFuse] Drop loop dispositions before reassigning blocks to other loop

This bug was found by recent improvement in SCEV verifier. The code in LoopFuse
directly reassigns blocks to be a part of a different loop, which should automatically
invalidate all related cached loop dispositions.

Differential Revision: https://reviews.llvm.org/D134173
Reviewed By: nikic

llvm/lib/Transforms/Scalar/LoopFuse.cpp

@@ -1696,6 +1696,7 @@ private:
     // mergeLatch may remove the only block in FC1.
     SE.forgetLoop(FC1.L);
     SE.forgetLoop(FC0.L);
+    SE.forgetLoopDispositions();
 
     // Move instructions from FC0.Latch to FC1.Latch.
     // Note: mergeLatch requires an updated DT.
@@ -1988,6 +1989,7 @@ private:
     // mergeLatch may remove the only block in FC1.
     SE.forgetLoop(FC1.L);
     SE.forgetLoop(FC0.L);
+    SE.forgetLoopDispositions();
 
     // Move instructions from FC0.Latch to FC1.Latch.
     // Note: mergeLatch requires an updated DT.

llvm/test/Transforms/LoopFusion/double_loop_nest_inner_guard.ll

@@ -1,7 +1,4 @@
 ; RUN: opt -S -loop-fusion < %s 2>&1 | FileCheck %s
-; XFAIL: *
-; REQUIRES: asserts
-; Fails due to incorrect cached loop disposition.
 
 ; Verify that LoopFusion can fuse two double-loop nests with guarded inner
 ; loops. Loops are in canonical form.

llvm/test/Transforms/LoopFusion/loop_nest.ll

@@ -1,7 +1,4 @@
 ; RUN: opt -S -loop-fusion < %s | FileCheck %s
-; XFAIL: *
-; REQUIRES: asserts
-; Fails due to incorrect cached loop disposition.
 ;
 ;    int A[1024][1024];
 ;    int B[1024][1024];

llvm/test/Transforms/LoopFusion/triple_loop_nest_inner_guard.ll

@@ -1,7 +1,4 @@
 ; RUN: opt -S -loop-fusion < %s 2>&1 | FileCheck %s
-; XFAIL: *
-; REQUIRES: asserts
-; Fails due to incorrect cached loop disposition.
 
 ; Verify that LoopFusion can fuse two triple-loop nests with guarded inner
 ; loops. Loops are in canonical form.