LoopRotate: remove the replace-arg-with-struct peephole optimization

This does not belong to loop-rotate and does not work with OSSA.
This peephole is covered by other optimizations.

Author: eeckstein

include/swift/SILOptimizer/Utils/SILSSAUpdater.h

@@ -35,10 +35,6 @@ class SILBasicBlock;
 class SILType;
 class SILUndef;
 
-/// Independent utility that canonicalizes BB arguments by reusing structurally
-/// equivalent arguments and replacing the original arguments with casts.
-SILValue replaceBBArgWithCast(SILPhiArgument *arg);
-
 /// This class updates SSA for a set of SIL instructions defined in multiple
 /// blocks.
 class SILSSAUpdater {

lib/SILOptimizer/LoopTransforms/LoopRotate.cpp

@@ -187,17 +187,6 @@ static void updateSSAForUseOfValue(
     updater.rewriteUse(*use);
   }
 
-  // Canonicalize inserted phis to avoid extra BB Args and if we find an address
-  // phi, stash it so we can handle it after we are done rewriting.
-  for (SILPhiArgument *arg : insertedPhis) {
-    if (SILValue inst = replaceBBArgWithCast(arg)) {
-      arg->replaceAllUsesWith(inst);
-      // DCE+SimplifyCFG runs as a post-pass cleanup.
-      // DCE replaces dead arg values with undef.
-      // SimplifyCFG deletes the dead BB arg.
-      continue;
-    }
-  }
 }
 
 static void

lib/SILOptimizer/Utils/SILSSAUpdater.cpp

@@ -494,82 +494,6 @@ Operand *UseWrapper::getOperand() {
   llvm_unreachable("uninitialize use type");
 }
 
-/// At least one value feeding the specified SILArgument is a Struct. Attempt to
-/// replace the Argument with a new Struct in the same block.
-///
-/// When we handle more types of casts, this can become a template.
-///
-/// ArgValues are the values feeding the specified Argument from each
-/// predecessor. They must be listed in order of Arg->getParent()->getPreds().
-static StructInst *
-replaceBBArgWithStruct(SILPhiArgument *phiArg,
-                       SmallVectorImpl<SILValue> &argValues) {
-
-  SILBasicBlock *phiBlock = phiArg->getParent();
-  auto *firstSI = dyn_cast<StructInst>(argValues[0]);
-  if (!firstSI)
-    return nullptr;
-
-  // Collect the BBArg index of each struct oper.
-  // e.g.
-  //   struct(A, B)
-  //   br (B, A)
-  // : ArgIdxForOper => {1, 0}
-  SmallVector<unsigned, 4> argIdxForOper;
-  for (unsigned operIdx : indices(firstSI->getElements())) {
-    bool foundMatchingArgIdx = false;
-    for (unsigned argIdx : indices(phiBlock->getArguments())) {
-      auto avIter = argValues.begin();
-      bool tryNextArgIdx = false;
-      for (SILBasicBlock *predBlock : phiBlock->getPredecessorBlocks()) {
-        // All argument values must be StructInst.
-        auto *predSI = dyn_cast<StructInst>(*avIter++);
-        if (!predSI)
-          return nullptr;
-        OperandValueArrayRef edgeValues =
-            getEdgeValuesForTerminator(predBlock->getTerminator(), phiBlock);
-        if (edgeValues[argIdx] != predSI->getElements()[operIdx]) {
-          tryNextArgIdx = true;
-          break;
-        }
-      }
-      if (!tryNextArgIdx) {
-        assert(avIter == argValues.end() &&
-               "# ArgValues does not match # BB preds");
-        foundMatchingArgIdx = true;
-        argIdxForOper.push_back(argIdx);
-        break;
-      }
-    }
-    if (!foundMatchingArgIdx)
-      return nullptr;
-  }
-
-  SmallVector<SILValue, 4> structArgs;
-  for (auto argIdx : argIdxForOper)
-    structArgs.push_back(phiBlock->getArgument(argIdx));
-
-  // TODO: We probably want to use a SILBuilderWithScope here. What should we
-  // use?
-  SILBuilder builder(phiBlock, phiBlock->begin());
-  return builder.createStruct(cast<StructInst>(argValues[0])->getLoc(),
-                              phiArg->getType(), structArgs);
-}
-
-/// Canonicalize BB arguments, replacing argument-of-casts with
-/// cast-of-arguments. This only eliminates existing arguments, replacing them
-/// with casts. No new arguments are created. This allows downstream pattern
-/// detection like induction variable analysis to succeed.
-///
-/// If Arg is replaced, return the cast instruction. Otherwise return nullptr.
-SILValue swift::replaceBBArgWithCast(SILPhiArgument *arg) {
-  SmallVector<SILValue, 4> argValues;
-  arg->getIncomingPhiValues(argValues);
-  if (isa<StructInst>(argValues[0]))
-    return replaceBBArgWithStruct(arg, argValues);
-  return nullptr;
-}
-
 namespace swift::test {
 // Arguments:
 // * the first arguments are values, which are added as "available values" to the SSA-updater

test/SILOptimizer/looprotate.sil

@@ -336,48 +336,6 @@ bb0(%a0 : $Int32):
   return %t1 : $()
 }
 
-// Test the SSA Updater utility: replaceBBArgWithCast().
-//
-// CHECK-LABEL: struct_arg
-// CHECK: bb0:
-// CHECK:  cond_br
-// CHECK: bb1:
-// CHECK:  br bb3
-// CHECK: bb3({{%.*}} : $Builtin.Int32, [[WORD:%.*]] : $Builtin.Int32
-// CHECK:  [[STRUCT:%[0-9]+]] = struct $Int32 ([[WORD]]
-// CHECK:  apply {{.*}}([[STRUCT]])
-// CHECK:  cond_br
-// CHECK: bb6({{.*}}):
-// CHECK:  return
-sil @struct_arg : $@convention(thin) () -> () {
-bb0:
-  %c0 = integer_literal $Builtin.Int32, 0
-  %c100 = integer_literal $Builtin.Int32, 100
-  br bb1(%c0 : $Builtin.Int32, %c0 : $Builtin.Int32)
-
-bb1(%a1 : $Builtin.Int32, %a0 : $Builtin.Int32):
-  %s0 = struct $Int32 (%a0 : $Builtin.Int32)
-  %z1 = builtin "cmp_eq_Word"(%a0 : $Builtin.Int32, %c100 : $Builtin.Int32) : $Builtin.Int1
-  cond_br %z1, bb2, bb3
-
-bb3:
-  %c1 = integer_literal $Builtin.Int32, 1
-  %z2 = integer_literal $Builtin.Int1, 0
-  %d1 = builtin "sadd_with_overflow_Word"(%a0 : $Builtin.Int32, %c1 : $Builtin.Int32, %z2 : $Builtin.Int1) : $(Builtin.Int32, Builtin.Int1)
-  %t1 = tuple_extract %d1 : $(Builtin.Int32, Builtin.Int1), 0
-  %d2 = builtin "sadd_with_overflow_Word"(%a1 : $Builtin.Int32, %c1 : $Builtin.Int32, %z2 : $Builtin.Int1) : $(Builtin.Int32, Builtin.Int1)
-  %t2 = tuple_extract %d2 : $(Builtin.Int32, Builtin.Int1), 0
-  %f1 = function_ref @readInt : $@convention(thin) (Int32) -> ()
-  %l1 = apply %f1(%s0) : $@convention(thin) (Int32) -> ()
-  br bb1(%t2 : $Builtin.Int32, %t1 : $Builtin.Int32)
-
-bb2:
-  %14 = struct $Int32 (%a1 : $Builtin.Int32)
-  %t3 = tuple ()
-  return %t3 : $()
-
-}
-
 // Test LoopRotate insertBackedgeBlock.
 //
 // CHECK-LABEL: insert_backedge_block

test/SILOptimizer/looprotate_ossa.sil

@@ -404,49 +404,6 @@ bb0(%a0 : $Int32):
   return %t1 : $()
 }
 
-// Test the SSA Updater utility: replaceBBArgWithCast().
-//
-// CHECK-LABEL: sil [ossa] @struct_arg :
-// CHECK: bb0:
-// CHECK:  cond_br
-// CHECK: bb1:
-// CHECK:  br bb3
-// CHECK: bb3({{%.*}} : $Builtin.Int32, [[WORD:%.*]] : $Builtin.Int32
-// CHECK:  [[STRUCT:%[0-9]+]] = struct $Int32 ([[WORD]]
-// CHECK:  apply {{.*}}([[STRUCT]])
-// CHECK:  cond_br
-// CHECK: bb6({{.*}}):
-// CHECK:  return
-// CHECK-LABEL: } // end sil function 'struct_arg'
-sil [ossa] @struct_arg : $@convention(thin) () -> () {
-bb0:
-  %c0 = integer_literal $Builtin.Int32, 0
-  %c100 = integer_literal $Builtin.Int32, 100
-  br bb1(%c0 : $Builtin.Int32, %c0 : $Builtin.Int32)
-
-bb1(%a1 : $Builtin.Int32, %a0 : $Builtin.Int32):
-  %s0 = struct $Int32 (%a0 : $Builtin.Int32)
-  %z1 = builtin "cmp_eq_Word"(%a0 : $Builtin.Int32, %c100 : $Builtin.Int32) : $Builtin.Int1
-  cond_br %z1, bb2, bb3
-
-bb3:
-  %c1 = integer_literal $Builtin.Int32, 1
-  %z2 = integer_literal $Builtin.Int1, 0
-  %d1 = builtin "sadd_with_overflow_Word"(%a0 : $Builtin.Int32, %c1 : $Builtin.Int32, %z2 : $Builtin.Int1) : $(Builtin.Int32, Builtin.Int1)
-  %t1 = tuple_extract %d1 : $(Builtin.Int32, Builtin.Int1), 0
-  %d2 = builtin "sadd_with_overflow_Word"(%a1 : $Builtin.Int32, %c1 : $Builtin.Int32, %z2 : $Builtin.Int1) : $(Builtin.Int32, Builtin.Int1)
-  %t2 = tuple_extract %d2 : $(Builtin.Int32, Builtin.Int1), 0
-  %f1 = function_ref @readInt : $@convention(thin) (Int32) -> ()
-  %l1 = apply %f1(%s0) : $@convention(thin) (Int32) -> ()
-  br bb1(%t2 : $Builtin.Int32, %t1 : $Builtin.Int32)
-
-bb2:
-  %14 = struct $Int32 (%a1 : $Builtin.Int32)
-  %t3 = tuple ()
-  return %t3 : $()
-
-}
-
 // Test LoopRotate insertBackedgeBlock.
 //
 // CHECK-LABEL: sil [ossa] @insert_backedge_block :