[JumpThreading] Remove cast's constraint

[aqjune]

Summary

As discussed in D84949, this removes the constraint to cast since it does not
cause compile time degradation.

[lebedev.ri]

lg

llvm/lib/Transforms/Scalar/JumpThreading.cpp

for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
         if (Constant *KC = getKnownConstant(CI, Preference))
           Result.emplace_back(KC, PN->getIncomingBlock(i));
       }
     }
 
     return !Result.empty();
   }
 
-  // Handle Cast instructions.  Only see through Cast when the source operand is
-  // PHI, Cmp, or Freeze to save the compilation time.
+  // Handle Cast instructions.
   if (CastInst *CI = dyn_cast<CastInst>(I)) {
     Value *Source = CI->getOperand(0);
-    if (!isa<PHINode>(Source) && !isa<CmpInst>(Source) &&
-        !isa<FreezeInst>(Source))
-      return false;
     ComputeValueKnownInPredecessorsImpl(Source, BB, Result, Preference,
                                         RecursionSet, CxtI);
     if (Result.empty())
       return false;
 
     // Convert the known values.
     for (auto &R : Result)
       R.first = ConstantExpr::getCast(CI->getOpcode(), R.first, CI->getType());

llvm/test/Transforms/JumpThreading/threadable-edge-cast.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -jump-threading -S < %s | FileCheck %s
 
 declare i32 @f1()
 declare i32 @f2()
 declare void @f3()
 
 ; trunc(and) should be simplified
 define i32 @test(i1 %cond0) {
 ; CHECK-LABEL: @test(
 ; CHECK-NEXT:    br i1 [[COND0:%.*]], label [[T1:%.*]], label [[F1:%.*]]
 ; CHECK:       T1:
 ; CHECK-NEXT:    [[V1:%.*]] = call i32 @f1()
-; CHECK-NEXT:    br label [[MERGE:%.*]]
+; CHECK-NEXT:    br label [[F2:%.*]]
 ; CHECK:       F1:
 ; CHECK-NEXT:    [[V2:%.*]] = call i32 @f2()
-; CHECK-NEXT:    br label [[MERGE]]
-; CHECK:       Merge:
+; CHECK-NEXT:    br label [[F2]]
+; CHECK:       F2:
 ; CHECK-NEXT:    [[A:%.*]] = phi i32 [ 10, [[T1]] ], [ 0, [[F1]] ]
 ; CHECK-NEXT:    [[B:%.*]] = phi i32 [ [[V1]], [[T1]] ], [ [[V2]], [[F1]] ]
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 [[A]], 1
-; CHECK-NEXT:    [[COND:%.*]] = trunc i32 [[AND]] to i1
-; CHECK-NEXT:    br i1 [[COND]], label [[T2:%.*]], label [[F2:%.*]]
-; CHECK:       T2:
-; CHECK-NEXT:    call void @f3()
-; CHECK-NEXT:    ret i32 [[B]]
-; CHECK:       F2:
 ; CHECK-NEXT:    ret i32 [[B]]
 ;
   br i1 %cond0, label %T1, label %F1
 T1:
   %v1 = call i32 @f1()
   br label %Merge
 
 F1:

 }
 
 ; trunc(select) should be simplified
 define i32 @test2(i1 %cond0) {
 ; CHECK-LABEL: @test2(
 ; CHECK-NEXT:    br i1 [[COND0:%.*]], label [[T1:%.*]], label [[F1:%.*]]
 ; CHECK:       T1:
 ; CHECK-NEXT:    [[V1:%.*]] = call i32 @f1()
-; CHECK-NEXT:    br label [[MERGE:%.*]]
+; CHECK-NEXT:    br label [[F2:%.*]]
 ; CHECK:       F1:
 ; CHECK-NEXT:    [[V2:%.*]] = call i32 @f2()
-; CHECK-NEXT:    br label [[MERGE]]
-; CHECK:       Merge:
+; CHECK-NEXT:    br label [[F2]]
+; CHECK:       F2:
 ; CHECK-NEXT:    [[A:%.*]] = phi i1 [ true, [[T1]] ], [ false, [[F1]] ]
 ; CHECK-NEXT:    [[B:%.*]] = phi i32 [ [[V1]], [[T1]] ], [ [[V2]], [[F1]] ]
 ; CHECK-NEXT:    [[A2:%.*]] = xor i1 [[A]], true
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[A2]], i32 10, i32 0
-; CHECK-NEXT:    [[COND:%.*]] = trunc i32 [[SEL]] to i1
-; CHECK-NEXT:    br i1 [[COND]], label [[T2:%.*]], label [[F2:%.*]]
-; CHECK:       T2:
-; CHECK-NEXT:    call void @f3()
-; CHECK-NEXT:    ret i32 [[B]]
-; CHECK:       F2:
 ; CHECK-NEXT:    ret i32 [[B]]
 ;
   br i1 %cond0, label %T1, label %F1
 T1:
   %v1 = call i32 @f1()
   br label %Merge
 
 F1: