[llvm] bb39372 - [Indvars][NFCI] Remove meaningless restrictive code in IndVars

[Max Kazantsev via llvm-commits]

Author: Max Kazantsev
Date: 2020-10-16T18:04:31+07:00
New Revision: bb39372e5e66e8d36735fa205d48e06c06a8fa00

URL: https://github.com/llvm/llvm-project/commit/bb39372e5e66e8d36735fa205d48e06c06a8fa00
DIFF: https://github.com/llvm/llvm-project/commit/bb39372e5e66e8d36735fa205d48e06c06a8fa00.diff

LOG: [Indvars][NFCI] Remove meaningless restrictive code in IndVars

Variable ExtendOperExpr only exists to check whether it is a SCEV ext.
We create it as SCEV ext right here, so semantically this check is
trivially true. In theory, it may fail if SCEV is smart enough and can
simplify the expression. However, no matter whether it is an ext or not,
we never use this fact for further reasoning. So this code is currently
useless and in theory may become harmful with SCEV's development.

We do not expect any behavior changes with removing it. If it caused
negative changes, the patch should be reverted.

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index bd609344af87..23001abf1d75 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1119,17 +1119,12 @@ bool WidenIV::widenWithVariantUse(NarrowIVDefUse DU) {
   assert(DU.NarrowUse->getOperand(1 - ExtendOperIdx) == DU.NarrowDef &&
          "bad DU");
 
-  const SCEV *ExtendOperExpr = nullptr;
   const OverflowingBinaryOperator *OBO =
     cast<OverflowingBinaryOperator>(NarrowUse);
   ExtendKind ExtKind = getExtendKind(NarrowDef);
-  if (ExtKind == SignExtended && OBO->hasNoSignedWrap())
-    ExtendOperExpr = SE->getSignExtendExpr(
-      SE->getSCEV(NarrowUse->getOperand(ExtendOperIdx)), WideType);
-  else if (ExtKind == ZeroExtended && OBO->hasNoUnsignedWrap())
-    ExtendOperExpr = SE->getZeroExtendExpr(
-      SE->getSCEV(NarrowUse->getOperand(ExtendOperIdx)), WideType);
-  else
+  bool CanSignExtend = ExtKind == SignExtended && OBO->hasNoSignedWrap();
+  bool CanZeroExtend = ExtKind == ZeroExtended && OBO->hasNoUnsignedWrap();
+  if (!CanSignExtend && !CanZeroExtend)
     return false;
 
   // Verifying that Defining operand is an AddRec
@@ -1137,14 +1132,6 @@ bool WidenIV::widenWithVariantUse(NarrowIVDefUse DU) {
   const SCEVAddRecExpr *AddRecOp1 = dyn_cast<SCEVAddRecExpr>(Op1);
   if (!AddRecOp1 || AddRecOp1->getLoop() != L)
     return false;
-  // Verifying that other operand is an Extend.
-  if (ExtKind == SignExtended) {
-    if (!isa<SCEVSignExtendExpr>(ExtendOperExpr))
-      return false;
-  } else {
-    if (!isa<SCEVZeroExtendExpr>(ExtendOperExpr))
-      return false;
-  }
 
   if (ExtKind == SignExtended) {
     for (Use &U : NarrowUse->uses()) {