[llvm] [X86] Fold C1 * C2 + Z --> C3 + Z for vpmadd52l/vpmadd52h (PR #156293)

[Simon Pilgrim via llvm-commits]

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@@ -44954,26 +44954,39 @@ bool X86TargetLowering::SimplifyDemandedBitsForTargetNode(
   }
   case X86ISD::VPMADD52L:
   case X86ISD::VPMADD52H: {
-    KnownBits KnownOp0, KnownOp1;
+    KnownBits Known52BitsOfOp0, Known52BitsOfOp1;
     SDValue Op0 = Op.getOperand(0);
     SDValue Op1 = Op.getOperand(1);
     SDValue Op2 = Op.getOperand(2);
     //  Only demand the lower 52-bits of operands 0 / 1 (and all 64-bits of
     //  operand 2).
     APInt Low52Bits = APInt::getLowBitsSet(BitWidth, 52);
-    if (SimplifyDemandedBits(Op0, Low52Bits, OriginalDemandedElts, KnownOp0,
-                             TLO, Depth + 1))
+    if (SimplifyDemandedBits(Op0, Low52Bits, OriginalDemandedElts,
+                             Known52BitsOfOp0, TLO, Depth + 1))
       return true;
 
-    if (SimplifyDemandedBits(Op1, Low52Bits, OriginalDemandedElts, KnownOp1,
-                             TLO, Depth + 1))
+    if (SimplifyDemandedBits(Op1, Low52Bits, OriginalDemandedElts,
+                             Known52BitsOfOp1, TLO, Depth + 1))
       return true;
 
-    // X * 0 + Y --> Y
-    // TODO: Handle cases where lower/higher 52 of bits of Op0 * Op1 are known
-    // zeroes.
-    if (KnownOp0.trunc(52).isZero() || KnownOp1.trunc(52).isZero())
-      return TLO.CombineTo(Op, Op2);
+    KnownBits KnownMul;
+    Known52BitsOfOp0 = Known52BitsOfOp0.trunc(52);
+    Known52BitsOfOp1 = Known52BitsOfOp1.trunc(52);
+    if (Opc == X86ISD::VPMADD52L) {
+      KnownMul =
+          KnownBits::mul(Known52BitsOfOp0.zext(104), Known52BitsOfOp1.zext(104))
+              .trunc(52);
+    } else {
+      KnownMul = KnownBits::mulhu(Known52BitsOfOp0, Known52BitsOfOp1);
+    }
+    KnownMul = KnownMul.zext(64);
+
+    // C1 * C2 + Z --> C3 + Z
+    if (KnownMul.isConstant()) {
+      SDValue C = TLO.DAG.getConstant(KnownMul.getConstant(), SDLoc(Op0), VT);
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RKSimon wrote:

Pull out repeated SDLoc()

https://github.com/llvm/llvm-project/pull/156293