Revert "[InstCombine] Remove side effect of replaced constrained intrinsics"

This reverts commit 83914ee.
The change caused discussion: https://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20220502/1034841.html

Author: spavloff

llvm/include/llvm/Analysis/InstructionSimplify.h

@@ -299,10 +299,6 @@ Value *SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS, FastMathFlags FMF,
                      const SimplifyQuery &Q);
 
 /// Given a callsite, fold the result or return null.
-///
-/// \note A call with declared side effect may be simplified into a value
-/// without such. It happens if simplification code deduces that side effect
-/// is actually absent.
 Value *SimplifyCall(CallBase *Call, const SimplifyQuery &Q);
 
 /// Given an operand for a Freeze, see if we can fold the result.

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -1237,16 +1237,6 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       return NewCall;
   }
 
-  // Unused constrained FP intrinsic calls may have declared side effect, which
-  // actually absent. If SimplifyCall returns a replacement for such call,
-  // assume side effect is absent and the call may be removed.
-  if (CI.use_empty() && isa<ConstrainedFPIntrinsic>(CI)) {
-    if (SimplifyCall(&CI, SQ.getWithInstruction(&CI))) {
-      eraseInstFromFunction(CI);
-      return nullptr;
-    }
-  }
-
   Intrinsic::ID IID = II->getIntrinsicID();
   switch (IID) {
   case Intrinsic::objectsize: