[NFC][Sink] Change runtime checks to asserts (#137354)

Candidate block for sinking must be dominated by current location. This
is true based on how the candidate block was selected. Runtime checks
are not necessary and has been changed to an assertion.

---------

Signed-off-by: John Lu <[email protected]>

Author: LU-JOHN

llvm/lib/Transforms/Scalar/Sink.cpp

@@ -82,11 +82,6 @@ static bool IsAcceptableTarget(Instruction *Inst, BasicBlock *SuccToSinkTo,
         !Inst->hasMetadata(LLVMContext::MD_invariant_load))
       return false;
 
-    // We don't want to sink across a critical edge if we don't dominate the
-    // successor. We could be introducing calculations to new code paths.
-    if (!DT.dominates(Inst->getParent(), SuccToSinkTo))
-      return false;
-
     // Don't sink instructions into a loop.
     Loop *succ = LI.getLoopFor(SuccToSinkTo);
     Loop *cur = LI.getLoopFor(Inst->getParent());
@@ -144,9 +139,6 @@ static bool SinkInstruction(Instruction *Inst,
       SuccToSinkTo = DT.findNearestCommonDominator(SuccToSinkTo, UseBlock);
     else
       SuccToSinkTo = UseBlock;
-    // The current basic block needs to dominate the candidate.
-    if (!DT.dominates(BB, SuccToSinkTo))
-      return false;
   }
 
   if (SuccToSinkTo) {
@@ -167,6 +159,12 @@ static bool SinkInstruction(Instruction *Inst,
              Inst->getParent()->printAsOperand(dbgs(), false); dbgs() << " -> ";
              SuccToSinkTo->printAsOperand(dbgs(), false); dbgs() << ")\n");
 
+  // The current location of Inst dominates all uses, thus it must dominate
+  // SuccToSinkTo, which is on the IDom chain between the nearest common
+  // dominator to all uses and the current location.
+  assert(DT.dominates(BB, SuccToSinkTo) &&
+         "SuccToSinkTo must be dominated by current Inst location!");
+
   // Move the instruction.
   Inst->moveBefore(SuccToSinkTo->getFirstInsertionPt());
   return true;