[llvm] 9abc593 - [TargetLowering][InstCombine] Simplify BSwap demanded bits code a little. NFC

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2022-01-20T10:45:17-08:00
New Revision: 9abc593e98891b4cd8ffd2ca308cabe6ea5d142f

URL: https://github.com/llvm/llvm-project/commit/9abc593e98891b4cd8ffd2ca308cabe6ea5d142f
DIFF: https://github.com/llvm/llvm-project/commit/9abc593e98891b4cd8ffd2ca308cabe6ea5d142f.diff

LOG: [TargetLowering][InstCombine] Simplify BSwap demanded bits code a little. NFC

Use alignDown instead of &= ~7.

Replace ResultBit with NLZ. (BitWidth - NLZ - NTZ == 8) so
(BitWidth - NTZ - 8 == NLZ).

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D117804

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
    llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 6af5609993795..3b53a5b8b7532 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1815,20 +1815,16 @@ bool TargetLowering::SimplifyDemandedBits(
     // Round NTZ down to the next byte.  If we have 11 trailing zeros, then
     // we need all the bits down to bit 8.  Likewise, round NLZ.  If we
     // have 14 leading zeros, round to 8.
-    NLZ &= ~7;
-    NTZ &= ~7;
+    NLZ = alignDown(NLZ, 8);
+    NTZ = alignDown(NTZ, 8);
     // If we need exactly one byte, we can do this transformation.
     if (BitWidth - NLZ - NTZ == 8) {
-      unsigned ResultBit = NTZ;
-      unsigned InputBit = BitWidth - NTZ - 8;
-
       // Replace this with either a left or right shift to get the byte into
       // the right place.
-      unsigned ShiftOpcode = InputBit > ResultBit ? ISD::SRL : ISD::SHL;
+      unsigned ShiftOpcode = NLZ > NTZ ? ISD::SRL : ISD::SHL;
       if (!TLO.LegalOperations() || isOperationLegal(ShiftOpcode, VT)) {
         EVT ShiftAmtTy = getShiftAmountTy(VT, DL);
-        unsigned ShiftAmount =
-            InputBit > ResultBit ? InputBit - ResultBit : ResultBit - InputBit;
+        unsigned ShiftAmount = NLZ > NTZ ? NLZ - NTZ : NTZ - NLZ;
         SDValue ShAmt = TLO.DAG.getConstant(ShiftAmount, dl, ShiftAmtTy);
         SDValue NewOp = TLO.DAG.getNode(ShiftOpcode, dl, VT, Src, ShAmt);
         return TLO.CombineTo(Op, NewOp);

diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 4dc712f325362..71a5ae24eead9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -800,22 +800,21 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
         // Round NTZ down to the next byte.  If we have 11 trailing zeros, then
         // we need all the bits down to bit 8.  Likewise, round NLZ.  If we
         // have 14 leading zeros, round to 8.
-        NLZ &= ~7;
-        NTZ &= ~7;
+        NLZ = alignDown(NLZ, 8);
+        NTZ = alignDown(NTZ, 8);
         // If we need exactly one byte, we can do this transformation.
-        if (BitWidth-NLZ-NTZ == 8) {
-          unsigned ResultBit = NTZ;
-          unsigned InputBit = BitWidth-NTZ-8;
-
+        if (BitWidth - NLZ - NTZ == 8) {
           // Replace this with either a left or right shift to get the byte into
           // the right place.
           Instruction *NewVal;
-          if (InputBit > ResultBit)
-            NewVal = BinaryOperator::CreateLShr(II->getArgOperand(0),
-                    ConstantInt::get(I->getType(), InputBit-ResultBit));
+          if (NLZ > NTZ)
+            NewVal = BinaryOperator::CreateLShr(
+                II->getArgOperand(0),
+                ConstantInt::get(I->getType(), NLZ - NTZ));
           else
-            NewVal = BinaryOperator::CreateShl(II->getArgOperand(0),
-                    ConstantInt::get(I->getType(), ResultBit-InputBit));
+            NewVal = BinaryOperator::CreateShl(
+                II->getArgOperand(0),
+                ConstantInt::get(I->getType(), NTZ - NLZ));
           NewVal->takeName(I);
           return InsertNewInstWith(NewVal, *I);
         }