[PATCH] D50432: [DAGCombiner] Reduce load widths of shifted masks

[Sam Parker via Phabricator via llvm-commits]

samparker updated this revision to Diff 181768.
samparker added a comment.

Changed the method of creating the final shl.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D50432/new/

https://reviews.llvm.org/D50432

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/ARM/and-load-combine.ll


Index: test/CodeGen/ARM/and-load-combine.ll
===================================================================
--- test/CodeGen/ARM/and-load-combine.ll
+++ test/CodeGen/ARM/and-load-combine.ll
@@ -1549,3 +1549,39 @@
   %and = and i64 %1, -281474976710656
   ret i64 %and
 }
+
+; ARM-LABEL: test27:
+; ARM:       @ %bb.0:
+; ARM-NEXT:    ldrb r1, [r0, #1]
+; ARM-NEXT:    lsl r1, r1, #16
+; ARM-NEXT:    str r1, [r0]
+; ARM-NEXT:    bx lr
+;
+; ARMEB-LABEL: test27:
+; ARMEB:     @ %bb.0:
+; ARMEB-NEXT:  ldrb r1, [r0, #2]
+; ARMEB-NEXT:  lsl r1, r1, #16
+; ARMEB-NEXT:  str r1, [r0]
+; ARMEB-NEXT:  bx lr
+;
+; THUMB1-LABEL: test27:
+; THUMB1:     @ %bb.0:
+; THUMB1-NEXT:  ldrb r1, [r0, #1]
+; THUMB1-NEXT:  lsls r1, r1, #16
+; THUMB1-NEXT:  str r1, [r0]
+; THUMB1-NEXT:  bx lr
+;
+; THUMB2-LABEL: test27:
+; THUMB2:       @ %bb.0:
+; THUMB2-NEXT:    ldrb r1, [r0, #1]
+; THUMB2-NEXT:    lsls r1, r1, #16
+; THUMB2-NEXT:    str r1, [r0]
+; THUMB2-NEXT:    bx lr
+define void @test27(i32* nocapture %ptr) {
+entry:
+  %0 = load i32, i32* %ptr, align 4
+  %and = and i32 %0, 65280
+  %shl = shl i32 %and, 8
+  store i32 %shl, i32* %ptr, align 4
+  ret void
+}
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4724,9 +4724,8 @@
     if (SDValue Res = ReduceLoadWidth(N)) {
       LoadSDNode *LN0 = N0->getOpcode() == ISD::ANY_EXTEND
         ? cast<LoadSDNode>(N0.getOperand(0)) : cast<LoadSDNode>(N0);
-
       AddToWorklist(N);
-      CombineTo(LN0, Res, Res.getValue(1));
+      DAG.ReplaceAllUsesOfValueWith(SDValue(LN0, 0), Res);
       return SDValue(N, 0);
     }
   }
@@ -9486,18 +9485,15 @@
     if (DAG.getDataLayout().isBigEndian())
       ShAmt = AdjustBigEndianShift(ShAmt);
 
-    // We're using a shifted mask, so the load now has an offset. This means we
-    // now need to shift right the mask to match the new load and then shift
-    // right the result of the AND.
-    const APInt &Mask = cast<ConstantSDNode>(N->getOperand(1))->getAPIntValue();
-    APInt ShiftedMask = Mask.lshr(ShAmt);
-    DAG.UpdateNodeOperands(N, Result, DAG.getConstant(ShiftedMask, DL, VT));
+    // We're using a shifted mask, so the load now has an offset. This means
+    // that data has been loaded into the lower bytes than it would have been
+    // before, so we need to shl the loaded data into the correct position in the
+    // register.
     SDValue ShiftC = DAG.getConstant(ShAmt, DL, VT);
-    SDValue Shifted = DAG.getNode(ISD::SHL, DL, VT, SDValue(N, 0),
-                                  ShiftC);
-    DAG.ReplaceAllUsesOfValueWith(SDValue(N, 0), Shifted);
-    DAG.UpdateNodeOperands(Shifted.getNode(), SDValue(N, 0), ShiftC);
+    Result = DAG.getNode(ISD::SHL, DL, VT, Result, ShiftC);
+    DAG.ReplaceAllUsesOfValueWith(SDValue(N, 0), Result);
   }
+
   // Return the new loaded value.
   return Result;
 }


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D50432.181768.patch
Type: text/x-patch
Size: 2987 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190115/f6eb559d/attachment.bin>