[InstCombine] Disable branch predicate canonicalization by default

[yrouban]

Summary

Disabling the branch predicate canonicalization in InstCombine might affect many users. This transform is expected to be done by SimplifyCFG (D84492, D84491).
This one line patch allows a simple revert and further investigation for any found issues.
In future this transformation with its flag should be removed from InstCombine.

[lebedev.ri]

Abandon now that D84763 has resolved the base problem?

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

 // for their entire lifetime. However, passes like DSE and instcombine can
 // delete stores to the alloca, leading to misleading and inaccurate debug
 // information. This flag can be removed when those passes are fixed.
 static cl::opt<unsigned> ShouldLowerDbgDeclare("instcombine-lower-dbg-declare",
                                                cl::Hidden, cl::init(true));
 
 static cl::opt<bool>
     CanonicalizeBranchPredicates("instcombine-canonicalize-branch-predicates",
-                                 cl::Hidden, cl::init(true),
+                                 cl::Hidden, cl::init(false),
                                  cl::desc("Canonicalize branch predicates"));
 
 Optional<Instruction *>
 InstCombiner::targetInstCombineIntrinsic(IntrinsicInst &II) {
   // Handle target specific intrinsics
   if (II.getCalledFunction()->isTargetIntrinsic()) {
     return TTI.instCombineIntrinsic(*this, II);
   }