[llvm] b665513 - [SelectionDAG] Handle NSW for ADD/SUB in computeKnownBits()

[Nikita Popov via llvm-commits]

Author: Dhruv Chawla
Date: 2023-05-17T15:15:05+02:00
New Revision: b66551370fdfc6f357ae0d77237119d2b1077b62

URL: https://github.com/llvm/llvm-project/commit/b66551370fdfc6f357ae0d77237119d2b1077b62
DIFF: https://github.com/llvm/llvm-project/commit/b66551370fdfc6f357ae0d77237119d2b1077b62.diff

LOG: [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

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
    llvm/test/CodeGen/Thumb2/mve-blockplacement.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index ffa9998949b40..11f873400fc0d 100644
--- 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 
diff erence 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 35197dc199f60..58f6e2a36b212 100644
--- 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 2d7126db12fab..41fd74d99356a 100644
--- 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