[llvm] 49623fa - [ValueTracking] computeKnownBitsFromShiftOperator use KnownBits direct for constant shift amounts.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-11-13T10:54:35Z
New Revision: 49623fa77a35de343e89ea2d8159ce719473ce71

URL: https://github.com/llvm/llvm-project/commit/49623fa77a35de343e89ea2d8159ce719473ce71
DIFF: https://github.com/llvm/llvm-project/commit/49623fa77a35de343e89ea2d8159ce719473ce71.diff

LOG: [ValueTracking] computeKnownBitsFromShiftOperator use KnownBits direct for constant shift amounts.

Let KnownBits shift handlers deal with out-of-range shift amounts.

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp

Removed: 
    


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diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index b369f2697e5c..0a18718fd9b5 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -993,8 +993,7 @@ static void computeKnownBitsFromShiftOperator(
   computeKnownBits(I->getOperand(1), DemandedElts, Known, Depth + 1, Q);
 
   if (Known.isConstant()) {
-    unsigned ShiftAmt = Known.getConstant().getLimitedValue(BitWidth - 1);
-    Known = KF(Known2, KnownBits::makeConstant(APInt(32, ShiftAmt)));
+    Known = KF(Known2, Known);
 
     // If the known bits conflict, this must be an overflowing left shift, so
     // the shift result is poison. We can return anything we want. Choose 0 for