[SelectionDAG] Handle NSW for ADD/SUB in computeKnownBits()

This patch is a continuation of D150110. It separates the cases for
ADD and SUB into their own cases so that computeForAddSub can be
directly called and the NSW flag passed. This allows better
optimization when the NSW flag is enabled, and allows fixing up the
TODO that was there previously in SimplifyDemandedBits.

Differential Revision: https://reviews.llvm.org/D150769

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index ffa9998..11f8734 100644 (file)
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3631,6 +3631,15 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
     // All bits are zero except the low bit.
     Known.Zero.setBitsFrom(1);
     break;
+  case ISD::ADD:
+  case ISD::SUB: {
+    SDNodeFlags Flags = Op.getNode()->getFlags();
+    Known = computeKnownBits(Op.getOperand(0), DemandedElts, Depth + 1);
+    Known2 = computeKnownBits(Op.getOperand(1), DemandedElts, Depth + 1);
+    Known = KnownBits::computeForAddSub(Op.getOpcode() == ISD::ADD,
+                                        Flags.hasNoSignedWrap(), Known, Known2);
+    break;
+  }
   case ISD::USUBO:
   case ISD::SSUBO:
   case ISD::USUBO_CARRY:
@@ -3644,7 +3653,6 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
       break;
     }
     [[fallthrough]];
-  case ISD::SUB:
   case ISD::SUBC: {
     assert(Op.getResNo() == 0 &&
            "We only compute knownbits for the difference here.");
@@ -3672,7 +3680,6 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
       break;
     }
     [[fallthrough]];
-  case ISD::ADD:
   case ISD::ADDC:
   case ISD::ADDE: {
     assert(Op.getResNo() == 0 && "We only compute knownbits for the sum here.");

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 35197dc..58f6e2a 100644 (file)
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -2694,11 +2694,9 @@ bool TargetLowering::SimplifyDemandedBits(
     if (Op.getOpcode() == ISD::MUL) {
       Known = KnownBits::mul(KnownOp0, KnownOp1);
     } else { // Op.getOpcode() is either ISD::ADD or ISD::SUB.
-      // TODO: Update `computeForAddCarry` to handle the NSW flag as well so
-      //       that `Flags.hasNoSignedWrap()` can be passed through here
-      //       instead of false.
-      Known = KnownBits::computeForAddSub(Op.getOpcode() == ISD::ADD, false,
-                                          KnownOp0, KnownOp1);
+      Known = KnownBits::computeForAddSub(Op.getOpcode() == ISD::ADD,
+                                          Flags.hasNoSignedWrap(), KnownOp0,
+                                          KnownOp1);
     }
     break;
   }

diff --git a/llvm/test/CodeGen/Thumb2/mve-blockplacement.ll b/llvm/test/CodeGen/Thumb2/mve-blockplacement.ll
index 2d7126d..41fd74d 100644 (file)
--- a/llvm/test/CodeGen/Thumb2/mve-blockplacement.ll
+++ b/llvm/test/CodeGen/Thumb2/mve-blockplacement.ll
@@ -366,18 +366,16 @@ define i32 @d(i64 %e, i32 %f, i64 %g, i32 %h) {
 ; CHECK-NEXT:    str r0, [sp, #12] @ 4-byte Spill
 ; CHECK-NEXT:    movs r1, #4
 ; CHECK-NEXT:    strd r2, r12, [sp, #4] @ 8-byte Folded Spill
-; CHECK-NEXT:    add.w r3, r3, r4, lsr #1
 ; CHECK-NEXT:    add.w r1, r1, r4, lsr #1
-; CHECK-NEXT:    movw r4, #65532
-; CHECK-NEXT:    vdup.32 q6, r3
-; CHECK-NEXT:    movt r4, #32767
-; CHECK-NEXT:    and.w r7, r1, r4
+; CHECK-NEXT:    add.w r3, r3, r4, lsr #1
+; CHECK-NEXT:    bic r7, r1, #3
 ; CHECK-NEXT:    adr r1, .LCPI1_0
-; CHECK-NEXT:    vdup.32 q7, r3
 ; CHECK-NEXT:    vldrw.u32 q0, [r1]
 ; CHECK-NEXT:    adr r1, .LCPI1_1
 ; CHECK-NEXT:    vldrw.u32 q5, [r1]
+; CHECK-NEXT:    vdup.32 q6, r3
 ; CHECK-NEXT:    vadd.i32 q4, q0, lr
+; CHECK-NEXT:    vdup.32 q7, r3
 ; CHECK-NEXT:    b .LBB1_4
 ; CHECK-NEXT:  .LBB1_2: @ %for.body6.preheader
 ; CHECK-NEXT:    @ in Loop: Header=BB1_4 Depth=1