[llvm] d374001 - [ValueTracking] computeKnownBitsFromShiftOperator - remove non-zero shift amount handling.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2021-02-24T13:49:13Z
New Revision: d37400168ce2f1f9ccc91847431f5b8c020a7d67

URL: https://github.com/llvm/llvm-project/commit/d37400168ce2f1f9ccc91847431f5b8c020a7d67
DIFF: https://github.com/llvm/llvm-project/commit/d37400168ce2f1f9ccc91847431f5b8c020a7d67.diff

LOG: [ValueTracking] computeKnownBitsFromShiftOperator - remove non-zero shift amount handling.

This no longer affects any tests after the improvements to the KnownBits shift helpers.

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 9e5c8b49767e..a979a7d8cbf2 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1018,15 +1018,10 @@ static void computeKnownBitsFromShiftOperator(
   // If we know the shifter operand is nonzero, we can sometimes infer more
   // known bits. However this is expensive to compute, so be lazy about it and
   // only compute it when absolutely necessary.
-  Optional<bool> ShifterOperandIsNonZero;
-
   // Early exit if we can't constrain any well-defined shift amount.
   if (!(ShiftAmtKZ & (PowerOf2Ceil(BitWidth) - 1)) &&
       !(ShiftAmtKO & (PowerOf2Ceil(BitWidth) - 1))) {
-    ShifterOperandIsNonZero =
-        isKnownNonZero(I->getOperand(1), DemandedElts, Depth + 1, Q);
-    if (!*ShifterOperandIsNonZero)
-      return;
+    return;
   }
 
   Known.Zero.setAllBits();
@@ -1038,17 +1033,6 @@ static void computeKnownBitsFromShiftOperator(
       continue;
     if ((ShiftAmt | ShiftAmtKO) != ShiftAmt)
       continue;
-    // If we know the shifter is nonzero, we may be able to infer more known
-    // bits. This check is sunk down as far as possible to avoid the expensive
-    // call to isKnownNonZero if the cheaper checks above fail.
-    if (ShiftAmt == 0) {
-      if (!ShifterOperandIsNonZero.hasValue())
-        ShifterOperandIsNonZero =
-            isKnownNonZero(I->getOperand(1), DemandedElts, Depth + 1, Q);
-      if (*ShifterOperandIsNonZero)
-        continue;
-    }
-
     Known = KnownBits::commonBits(
         Known, KF(Known2, KnownBits::makeConstant(APInt(32, ShiftAmt))));
   }