[Reassociate] Invalidate analysis passes after canonicalizeOperands

When ranking operands for an expression tree the reassociate pass
also perform canonicalization, putting constants on the right
hand side. Such transforms was however not registered as modifying
the IR. So at the end of the pass, if not having made any other
changes, the pass returned that all analyses should be kept.

With this patch we make sure to set MadeChange to true when
modifying the IR via canonicalizeOperands. This is to make sure
analyses such as DemandedBits are properly invalidated when
instructions are modified.

Author: bjope

llvm/lib/Transforms/Scalar/Reassociate.cpp

@@ -241,8 +241,10 @@ void ReassociatePass::canonicalizeOperands(Instruction *I) {
   Value *RHS = I->getOperand(1);
   if (LHS == RHS || isa<Constant>(RHS))
     return;
-  if (isa<Constant>(LHS) || getRank(RHS) < getRank(LHS))
+  if (isa<Constant>(LHS) || getRank(RHS) < getRank(LHS)) {
     cast<BinaryOperator>(I)->swapOperands();
+    MadeChange = true;
+  }
 }
 
 static BinaryOperator *CreateAdd(Value *S1, Value *S2, const Twine &Name,

llvm/test/Transforms/Reassociate/canonicalize-made-change.ll

@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes="print<demanded-bits>,reassociate,bdce" -S < %s | FileCheck %s
+
+; We want to verify that demanded-bits analysis is invalidated when
+; reassociate is canonicalizing expressions (e.g. putting the constant on the
+; RHS of an OR).
+;
+; Printing demanded-bits will make sure a demanded-bits analysis is cached.
+; Then we run reassociate, followed by bdce. When not invalidating demanded-bits
+; while doing reassociation of the OR, we got this kind of error:
+;
+;   Running pass: BDCEPass on foo (4 instructions)
+;   While deleting: i1 %cmp1
+;   Use still stuck around after Def is destroyed:  %or = or i1 %cmp1, true
+;   UNREACHABLE executed at ../lib/IR/Value.cpp:102!
+;
+; Check that we get the expected result without failing on assert/unreachable.
+
+define i1 @foo(i1 %c) {
+; CHECK-LABEL: define i1 @foo(
+; CHECK-SAME: i1 [[C:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[OR:%.*]] = or i1 false, true
+; CHECK-NEXT:    [[AND:%.*]] = and i1 [[OR]], [[C]]
+; CHECK-NEXT:    ret i1 [[AND]]
+;
+entry:
+  %cmp = icmp ne i16 0, 1
+  %or = or i1 true, %cmp
+  %and = and i1 %c, %or
+  ret i1 %and
+}