[llvm] 7cbfb4e - [RISCV] Select (srl (and X, C2) as (slli (srliw X, C3), C3-C).

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2022-06-29T09:15:09-07:00
New Revision: 7cbfb4eb7a9e24ede4a59e9c08d91747d8475e03

URL: https://github.com/llvm/llvm-project/commit/7cbfb4eb7a9e24ede4a59e9c08d91747d8475e03
DIFF: https://github.com/llvm/llvm-project/commit/7cbfb4eb7a9e24ede4a59e9c08d91747d8475e03.diff

LOG: [RISCV] Select (srl (and X, C2) as (slli (srliw X, C3), C3-C).

If C2 has 32 leading zeros and C3 trailing zeros.

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
    llvm/test/CodeGen/RISCV/copysign-casts.ll
    llvm/test/CodeGen/RISCV/selectcc-to-shiftand.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp b/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
index 3c3412e82a171..74dda1fe6e91c 100644
--- a/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
@@ -712,13 +712,6 @@ void RISCVDAGToDAGISel::Select(SDNode *Node) {
     return;
   }
   case ISD::SRL: {
-    // Optimize (srl (and X, C2), C) ->
-    //          (srli (slli X, (XLen-C3), (XLen-C3) + C)
-    // Where C2 is a mask with C3 trailing ones.
-    // Taking into account that the C2 may have had lower bits unset by
-    // SimplifyDemandedBits. This avoids materializing the C2 immediate.
-    // This pattern occurs when type legalizing right shifts for types with
-    // less than XLen bits.
     auto *N1C = dyn_cast<ConstantSDNode>(Node->getOperand(1));
     if (!N1C)
       break;
@@ -728,6 +721,32 @@ void RISCVDAGToDAGISel::Select(SDNode *Node) {
       break;
     unsigned ShAmt = N1C->getZExtValue();
     uint64_t Mask = N0.getConstantOperandVal(1);
+
+    // Optimize (srl (and X, C2), C) -> (slli (srliw X, C3), C3-C) where C2 has
+    // 32 leading zeros and C3 trailing zeros.
+    if (isShiftedMask_64(Mask)) {
+      unsigned XLen = Subtarget->getXLen();
+      unsigned LeadingZeros = XLen - (64 - countLeadingZeros(Mask));
+      unsigned TrailingZeros = countTrailingZeros(Mask);
+      if (LeadingZeros == 32 && TrailingZeros > ShAmt) {
+        SDNode *SRLIW = CurDAG->getMachineNode(
+            RISCV::SRLIW, DL, VT, N0->getOperand(0),
+            CurDAG->getTargetConstant(TrailingZeros, DL, VT));
+        SDNode *SLLI = CurDAG->getMachineNode(
+            RISCV::SLLI, DL, VT, SDValue(SRLIW, 0),
+            CurDAG->getTargetConstant(TrailingZeros - ShAmt, DL, VT));
+        ReplaceNode(Node, SLLI);
+        return;
+      }
+    }
+
+    // Optimize (srl (and X, C2), C) ->
+    //          (srli (slli X, (XLen-C3), (XLen-C3) + C)
+    // Where C2 is a mask with C3 trailing ones.
+    // Taking into account that the C2 may have had lower bits unset by
+    // SimplifyDemandedBits. This avoids materializing the C2 immediate.
+    // This pattern occurs when type legalizing right shifts for types with
+    // less than XLen bits.
     Mask |= maskTrailingOnes<uint64_t>(ShAmt);
     if (!isMask_64(Mask))
       break;

diff  --git a/llvm/test/CodeGen/RISCV/copysign-casts.ll b/llvm/test/CodeGen/RISCV/copysign-casts.ll
index 42ea6958a9d1b..8d44178437807 100644
--- a/llvm/test/CodeGen/RISCV/copysign-casts.ll
+++ b/llvm/test/CodeGen/RISCV/copysign-casts.ll
@@ -341,10 +341,8 @@ define half @fold_demote_h_s(half %a, float %b) nounwind {
 ;
 ; RV64I-LABEL: fold_demote_h_s:
 ; RV64I:       # %bb.0:
-; RV64I-NEXT:    li a2, 1
-; RV64I-NEXT:    slli a2, a2, 31
-; RV64I-NEXT:    and a1, a1, a2
-; RV64I-NEXT:    srli a1, a1, 16
+; RV64I-NEXT:    srliw a1, a1, 31
+; RV64I-NEXT:    slli a1, a1, 15
 ; RV64I-NEXT:    slli a0, a0, 49
 ; RV64I-NEXT:    srli a0, a0, 49
 ; RV64I-NEXT:    or a0, a0, a1

diff  --git a/llvm/test/CodeGen/RISCV/selectcc-to-shiftand.ll b/llvm/test/CodeGen/RISCV/selectcc-to-shiftand.ll
index a10c6945b7d0b..94366071849ac 100644
--- a/llvm/test/CodeGen/RISCV/selectcc-to-shiftand.ll
+++ b/llvm/test/CodeGen/RISCV/selectcc-to-shiftand.ll
@@ -37,10 +37,8 @@ define i32 @neg_sel_special_constant(i32 signext %a) {
 ;
 ; RV64-LABEL: neg_sel_special_constant:
 ; RV64:       # %bb.0:
-; RV64-NEXT:    li a1, 1
-; RV64-NEXT:    slli a1, a1, 31
-; RV64-NEXT:    and a0, a0, a1
-; RV64-NEXT:    srli a0, a0, 22
+; RV64-NEXT:    srliw a0, a0, 31
+; RV64-NEXT:    slli a0, a0, 9
 ; RV64-NEXT:    ret
   %tmp.1 = icmp slt i32 %a, 0
   %retval = select i1 %tmp.1, i32 512, i32 0