[llvm] 025a2f7 - [InstCombine] add tests for umax with sub; NFC

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2021-11-06T08:32:52-04:00
New Revision: 025a2f73a31955cfd9b1e097533b9c6ef15dc6d3

URL: https://github.com/llvm/llvm-project/commit/025a2f73a31955cfd9b1e097533b9c6ef15dc6d3
DIFF: https://github.com/llvm/llvm-project/commit/025a2f73a31955cfd9b1e097533b9c6ef15dc6d3.diff

LOG: [InstCombine] add tests for umax with sub; NFC

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    llvm/test/Transforms/InstCombine/minmax-intrinsics.ll

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 07a2ac8db5112..7888712d5107e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9575,6 +9575,23 @@ static SDValue foldVSelectToSignBitSplatMask(SDNode *N, SelectionDAG &DAG) {
     return DAG.getNode(ISD::OR, DL, VT, Sra, N2);
   }
 
+  // If the comparison is testing for a positive value, we have to invert
+  // the sign bit mask, so only do that transform if the target has a bitwise
+  // 'and not' instruction (the invert is free).
+  // (Cond0 s> -1) ? N1 : 0 --> ~(Cond0 s>> BW-1) & N1
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+  if (CC == ISD::SETGT && isAllOnesOrAllOnesSplat(Cond1) &&
+      isNullOrNullSplat(N2) && TLI.hasAndNot(N2)) {
+    SDLoc DL(N);
+    SDValue ShiftAmt = DAG.getConstant(VT.getScalarSizeInBits() - 1, DL, VT);
+    SDValue Sra = DAG.getNode(ISD::SRA, DL, VT, Cond0, ShiftAmt);
+    SDValue Not = DAG.getNOT(DL, Sra, VT);
+    return DAG.getNode(ISD::AND, DL, VT, Not, N1);
+  }
+  // (X >  0) ? X : 0 <-- This is canonical signed max.
+//    if (!(isAllOnesConstant(N1) || (isNullConstant(N1) && N0 == N2)))
+//      return SDValue();
+
   return SDValue();
 }
 

diff  --git a/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll b/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
index 7b76c3ad74226..573ed8eb12110 100644
--- a/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
+++ b/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
@@ -2129,3 +2129,27 @@ define <3 x i8> @umax_vector_splat_undef(<3 x i8> %x) {
   %r = call <3 x i8> @llvm.umax.v3i8(<3 x i8> %a, <3 x i8> <i8 13, i8 130, i8 130>)
   ret <3 x i8> %r
 }
+
+define <3 x i8> @umax_sub_vec(<3 x i8> %x, <3 x i8> %y) {
+; CHECK-LABEL: @umax_sub_vec(
+; CHECK-NEXT:    [[U:%.*]] = call <3 x i8> @llvm.umax.v3i8(<3 x i8> [[X:%.*]], <3 x i8> [[Y:%.*]])
+; CHECK-NEXT:    [[R:%.*]] = sub <3 x i8> [[U]], [[Y]]
+; CHECK-NEXT:    ret <3 x i8> [[R]]
+;
+  %u = call <3 x i8> @llvm.umax.v3i8(<3 x i8> %x, <3 x i8> %y)
+  %r = sub <3 x i8> %u, %y
+  ret <3 x i8> %r
+}
+
+define i8 @umax_sub_use(i8 %x, i8 %y) {
+; CHECK-LABEL: @umax_sub_use(
+; CHECK-NEXT:    [[U:%.*]] = call i8 @llvm.umax.i8(i8 [[X:%.*]], i8 [[Y:%.*]])
+; CHECK-NEXT:    call void @use(i8 [[U]])
+; CHECK-NEXT:    [[R:%.*]] = sub i8 [[U]], [[Y]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %u = call i8 @llvm.umax.i8(i8 %x, i8 %y)
+  call void @use(i8 %u)
+  %r = sub i8 %u, %y
+  ret i8 %r
+}