[TargetLowering] SimplifyDemandedBits ISD::SRA multi-use handling

RKSimon · RKSimon · commit f04284cf1d49 · 2020-01-21T15:12:07.000Z
Call SimplifyMultipleUseDemandedBits to peek through extended source args with multiple uses
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1534,6 +1534,16 @@ bool TargetLowering::SimplifyDemandedBits(
       if (Known.One[BitWidth - ShAmt - 1])
         // New bits are known one.
         Known.One.setHighBits(ShAmt);
+
+      // Attempt to avoid multi-use ops if we don't need anything from them.
+      if (!InDemandedMask.isAllOnesValue() || !DemandedElts.isAllOnesValue()) {
+        SDValue DemandedOp0 = SimplifyMultipleUseDemandedBits(
+            Op0, InDemandedMask, DemandedElts, TLO.DAG, Depth + 1);
+        if (DemandedOp0) {
+          SDValue NewOp = TLO.DAG.getNode(ISD::SRA, dl, VT, DemandedOp0, Op1);
+          return TLO.CombineTo(Op, NewOp);
+        }
+      }
     }
     break;
   }
diff --git a/llvm/test/CodeGen/X86/const-shift-of-constmasked.ll b/llvm/test/CodeGen/X86/const-shift-of-constmasked.ll
@@ -1870,9 +1870,9 @@ define i64 @test_i64_18446744065119617024_mask_ashr_1(i64 %a0) {
 define i64 @test_i64_18446744065119617024_mask_ashr_32(i64 %a0) {
 ; X32-LABEL: test_i64_18446744065119617024_mask_ashr_32:
 ; X32:       # %bb.0:
-; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X32-NEXT:    movl {{[0-9]+}}(%esp), %edx
+; X32-NEXT:    movl %edx, %eax
 ; X32-NEXT:    andl $-2, %eax
-; X32-NEXT:    movl %eax, %edx
 ; X32-NEXT:    sarl $31, %edx
 ; X32-NEXT:    retl
 ;
