[llvm] 058964d - [X86] LowerSELECTWithCmpZero - move "select (X != 0), -1, Y --> 0 - X; or (sbb), Y" fold

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2024-09-08T12:24:28+01:00
New Revision: 058964d3dacdc1321dcf2fdf82bebd3a37fcbc9c

URL: https://github.com/llvm/llvm-project/commit/058964d3dacdc1321dcf2fdf82bebd3a37fcbc9c
DIFF: https://github.com/llvm/llvm-project/commit/058964d3dacdc1321dcf2fdf82bebd3a37fcbc9c.diff

LOG: [X86] LowerSELECTWithCmpZero - move "select (X != 0), -1, Y --> 0 - X; or (sbb), Y" fold

Move fold into LowerSELECTWithCmpZero so it can be used with (AND X,1) ==/!= 0 select cases

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp
    llvm/test/CodeGen/X86/cmov-promotion.ll

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index b8a6f10cab623d..b9a6eb26fc9fcd 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -24139,6 +24139,32 @@ static SDValue LowerSELECTWithCmpZero(SDValue CmpVal, SDValue LHS, SDValue RHS,
     }
   }
 
+  if ((X86CC == X86::COND_E || X86CC == X86::COND_NE) &&
+      (isAllOnesConstant(LHS) || isAllOnesConstant(RHS))) {
+    SDValue Y = isAllOnesConstant(RHS) ? LHS : RHS;
+    SDVTList CmpVTs = DAG.getVTList(CmpVT, MVT::i32);
+
+    // 'X - 1' sets the carry flag if X == 0.
+    // '0 - X' sets the carry flag if X != 0.
+    // Convert the carry flag to a -1/0 mask with sbb:
+    // select (X != 0), -1, Y --> 0 - X; or (sbb), Y
+    // select (X == 0), Y, -1 --> 0 - X; or (sbb), Y
+    // select (X != 0), Y, -1 --> X - 1; or (sbb), Y
+    // select (X == 0), -1, Y --> X - 1; or (sbb), Y
+    SDValue Sub;
+    if (isAllOnesConstant(LHS) == (X86CC == X86::COND_NE)) {
+      SDValue Zero = DAG.getConstant(0, DL, CmpVT);
+      Sub = DAG.getNode(X86ISD::SUB, DL, CmpVTs, Zero, CmpVal);
+    } else {
+      SDValue One = DAG.getConstant(1, DL, CmpVT);
+      Sub = DAG.getNode(X86ISD::SUB, DL, CmpVTs, CmpVal, One);
+    }
+    SDValue SBB = DAG.getNode(X86ISD::SETCC_CARRY, DL, VT,
+                              DAG.getTargetConstant(X86::COND_B, DL, MVT::i8),
+                              Sub.getValue(1));
+    return DAG.getNode(ISD::OR, DL, VT, SBB, Y);
+  }
+
   return SDValue();
 }
 
@@ -24262,30 +24288,6 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) const {
         ((CondCode == X86::COND_NE && MatchFFSMinus1(Op1, Op2)) ||
          (CondCode == X86::COND_E && MatchFFSMinus1(Op2, Op1)))) {
       // Keep Cmp.
-    } else if ((isAllOnesConstant(Op1) || isAllOnesConstant(Op2)) &&
-        (CondCode == X86::COND_E || CondCode == X86::COND_NE)) {
-      SDValue Y = isAllOnesConstant(Op2) ? Op1 : Op2;
-      SDVTList CmpVTs = DAG.getVTList(CmpOp0.getValueType(), MVT::i32);
-
-      // 'X - 1' sets the carry flag if X == 0.
-      // '0 - X' sets the carry flag if X != 0.
-      // Convert the carry flag to a -1/0 mask with sbb:
-      // select (X != 0), -1, Y --> 0 - X; or (sbb), Y
-      // select (X == 0), Y, -1 --> 0 - X; or (sbb), Y
-      // select (X != 0), Y, -1 --> X - 1; or (sbb), Y
-      // select (X == 0), -1, Y --> X - 1; or (sbb), Y
-      SDValue Sub;
-      if (isAllOnesConstant(Op1) == (CondCode == X86::COND_NE)) {
-        SDValue Zero = DAG.getConstant(0, DL, CmpOp0.getValueType());
-        Sub = DAG.getNode(X86ISD::SUB, DL, CmpVTs, Zero, CmpOp0);
-      } else {
-        SDValue One = DAG.getConstant(1, DL, CmpOp0.getValueType());
-        Sub = DAG.getNode(X86ISD::SUB, DL, CmpVTs, CmpOp0, One);
-      }
-      SDValue SBB = DAG.getNode(X86ISD::SETCC_CARRY, DL, VT,
-                                DAG.getTargetConstant(X86::COND_B, DL, MVT::i8),
-                                Sub.getValue(1));
-      return DAG.getNode(ISD::OR, DL, VT, SBB, Y);
     } else if (SDValue R = LowerSELECTWithCmpZero(CmpOp0, Op1, Op2, CondCode,
                                                   DL, DAG, Subtarget)) {
       return R;

diff  --git a/llvm/test/CodeGen/X86/cmov-promotion.ll b/llvm/test/CodeGen/X86/cmov-promotion.ll
index e96faa7fbb7e7e..ff84fa4606ea0d 100644
--- a/llvm/test/CodeGen/X86/cmov-promotion.ll
+++ b/llvm/test/CodeGen/X86/cmov-promotion.ll
@@ -251,19 +251,16 @@ define i64 @cmov_spromotion_16_to_64(i1 %c) {
 ;
 ; NO_CMOV-LABEL: cmov_spromotion_16_to_64:
 ; NO_CMOV:       # %bb.0:
-; NO_CMOV-NEXT:    xorl %edx, %edx
-; NO_CMOV-NEXT:    testb $1, {{[0-9]+}}(%esp)
+; NO_CMOV-NEXT:    movzbl {{[0-9]+}}(%esp), %ecx
+; NO_CMOV-NEXT:    andb $1, %cl
 ; NO_CMOV-NEXT:    movl $12414, %eax # imm = 0x307E
-; NO_CMOV-NEXT:    je .LBB10_1
-; NO_CMOV-NEXT:  # %bb.2:
-; NO_CMOV-NEXT:    je .LBB10_3
-; NO_CMOV-NEXT:  .LBB10_4:
-; NO_CMOV-NEXT:    retl
-; NO_CMOV-NEXT:  .LBB10_1:
+; NO_CMOV-NEXT:    jne .LBB10_2
+; NO_CMOV-NEXT:  # %bb.1:
 ; NO_CMOV-NEXT:    movl $-22429, %eax # imm = 0xA863
-; NO_CMOV-NEXT:    jne .LBB10_4
-; NO_CMOV-NEXT:  .LBB10_3:
-; NO_CMOV-NEXT:    movl $-1, %edx
+; NO_CMOV-NEXT:  .LBB10_2:
+; NO_CMOV-NEXT:    xorl %edx, %edx
+; NO_CMOV-NEXT:    cmpb $1, %cl
+; NO_CMOV-NEXT:    sbbl %edx, %edx
 ; NO_CMOV-NEXT:    retl
   %t0 = select i1 %c, i16 12414, i16 43107
   %ret = sext i16 %t0 to i64