[PATCH] D55355: [X86] Directly create ADC/SBB nodes instead of using ADD/SUB with (and SETCC_CARRY, 1)

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: RKSimon, spatel.

This addresses a FIXME and avoids depending on an isel pattern match I think.

I'm trying to decide if we need SETCC_CARRY. This removes one of its usages.


Repository:
  rL LLVM

https://reviews.llvm.org/D55355

Files:
  lib/Target/X86/X86ISelLowering.cpp


Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -39992,18 +39992,6 @@
   return SDValue();
 }
 
-/// Materialize "setb reg" as "sbb reg,reg", since it produces an all-ones bit
-/// which is more useful than 0/1 in some cases.
-static SDValue materializeSBB(SDNode *N, SDValue EFLAGS, SelectionDAG &DAG) {
-  SDLoc DL(N);
-  // "Condition code B" is also known as "the carry flag" (CF).
-  SDValue CF = DAG.getConstant(X86::COND_B, DL, MVT::i8);
-  SDValue SBB = DAG.getNode(X86ISD::SETCC_CARRY, DL, MVT::i8, CF, EFLAGS);
-  MVT VT = N->getSimpleValueType(0);
-  assert(VT == MVT::i8 && "Unexpected type for SETCC node");
-  return DAG.getNode(ISD::AND, DL, VT, SBB, DAG.getConstant(1, DL, VT));
-}
-
 /// If this is an add or subtract where one operand is produced by a cmp+setcc,
 /// then try to convert it to an ADC or SBB. This replaces TEST+SET+{ADD/SUB}
 /// with CMP+{ADC, SBB}.
@@ -40074,13 +40062,11 @@
   }
 
   if (CC == X86::COND_B) {
-    // X + SETB Z --> X + (mask SBB Z, Z)
-    // X - SETB Z --> X - (mask SBB Z, Z)
-    // TODO: Produce ADC/SBB here directly and avoid SETCC_CARRY?
-    SDValue SBB = materializeSBB(Y.getNode(), Y.getOperand(1), DAG);
-    if (SBB.getValueSizeInBits() != VT.getSizeInBits())
-      SBB = DAG.getZExtOrTrunc(SBB, DL, VT);
-    return DAG.getNode(IsSub ? ISD::SUB : ISD::ADD, DL, VT, X, SBB);
+    // X + SETB Z --> adc X, 0
+    // X - SETB Z --> sbb X, 0
+    return DAG.getNode(IsSub ? X86ISD::SBB : X86ISD::ADC, DL,
+                       DAG.getVTList(VT, MVT::i32), X,
+                       DAG.getConstant(0, DL, VT), Y.getOperand(1));
   }
 
   if (CC == X86::COND_A) {
@@ -40098,10 +40084,9 @@
                                    EFLAGS.getNode()->getVTList(),
                                    EFLAGS.getOperand(1), EFLAGS.getOperand(0));
       SDValue NewEFLAGS = SDValue(NewSub.getNode(), EFLAGS.getResNo());
-      SDValue SBB = materializeSBB(Y.getNode(), NewEFLAGS, DAG);
-      if (SBB.getValueSizeInBits() != VT.getSizeInBits())
-        SBB = DAG.getZExtOrTrunc(SBB, DL, VT);
-      return DAG.getNode(IsSub ? ISD::SUB : ISD::ADD, DL, VT, X, SBB);
+      return DAG.getNode(IsSub ? X86ISD::SBB : X86ISD::ADC, DL,
+                         DAG.getVTList(VT, MVT::i32), X,
+                         DAG.getConstant(0, DL, VT), NewEFLAGS);
     }
   }
 


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