[X86] Use custom isel for (X86sbb_flag 0, 0) so we can use 32-bit SBB for i8/i16.

We were using MOV32r0 and an extract_subreg as an input. By using
custom isel we can move the extract_subreg to after the SBB instead
of on the input.

Author: topperc

llvm/lib/Target/X86/X86ISelDAGToDAG.cpp

@@ -5343,12 +5343,11 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
     // We have to do this manually because tblgen will put the eflags copy in
     // the wrong place if we use an extract_subreg in the pattern.
     MVT VT = Node->getSimpleValueType(0);
-    SDValue Chain = CurDAG->getEntryNode();
 
     // Copy flags to the EFLAGS register and glue it to next node.
-    SDValue EFLAGS = CurDAG->getCopyToReg(Chain, dl, X86::EFLAGS,
-                                          Node->getOperand(1), SDValue());
-    Chain = EFLAGS;
+    SDValue EFLAGS =
+        CurDAG->getCopyToReg(CurDAG->getEntryNode(), dl, X86::EFLAGS,
+                             Node->getOperand(1), SDValue());
 
     // Create a 64-bit instruction if the result is 64-bits otherwise use the
     // 32-bit version.
@@ -5367,6 +5366,56 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
     CurDAG->RemoveDeadNode(Node);
     return;
   }
+  case X86ISD::SBB: {
+    if (isNullConstant(Node->getOperand(0)) &&
+        isNullConstant(Node->getOperand(1))) {
+      MVT VT = Node->getSimpleValueType(0);
+
+      // Create zero.
+      SDVTList VTs = CurDAG->getVTList(MVT::i32, MVT::i32);
+      SDValue Zero =
+          SDValue(CurDAG->getMachineNode(X86::MOV32r0, dl, VTs, None), 0);
+      if (VT == MVT::i64) {
+        Zero = SDValue(
+            CurDAG->getMachineNode(
+                TargetOpcode::SUBREG_TO_REG, dl, MVT::i64,
+                CurDAG->getTargetConstant(0, dl, MVT::i64), Zero,
+                CurDAG->getTargetConstant(X86::sub_32bit, dl, MVT::i32)),
+            0);
+      }
+
+      // Copy flags to the EFLAGS register and glue it to next node.
+      SDValue EFLAGS =
+          CurDAG->getCopyToReg(CurDAG->getEntryNode(), dl, X86::EFLAGS,
+                               Node->getOperand(2), SDValue());
+
+      // Create a 64-bit instruction if the result is 64-bits otherwise use the
+      // 32-bit version.
+      unsigned Opc = VT == MVT::i64 ? X86::SBB64rr : X86::SBB32rr;
+      MVT SBBVT = VT == MVT::i64 ? MVT::i64 : MVT::i32;
+      VTs = CurDAG->getVTList(SBBVT, MVT::i32);
+      SDValue Result =
+          SDValue(CurDAG->getMachineNode(Opc, dl, VTs, {Zero, Zero, EFLAGS,
+                                         EFLAGS.getValue(1)}),
+                  0);
+
+      // Replace the flag use.
+      ReplaceUses(SDValue(Node, 1), Result.getValue(1));
+
+      // Replace the result use.
+      if (!SDValue(Node, 0).use_empty()) {
+        // For less than 32-bits we need to extract from the 32-bit node.
+        if (VT == MVT::i8 || VT == MVT::i16) {
+          int SubIndex = VT == MVT::i16 ? X86::sub_16bit : X86::sub_8bit;
+          Result = CurDAG->getTargetExtractSubreg(SubIndex, dl, VT, Result);
+        }
+        ReplaceUses(SDValue(Node, 0), Result);
+      }
+
+      CurDAG->RemoveDeadNode(Node);
+      return;
+    }
+  }
   }
 
   SelectCode(Node);

llvm/lib/Target/X86/X86InstrCompiler.td

@@ -334,22 +334,6 @@ def SETB_C32r : I<0, Pseudo, (outs GR32:$dst), (ins), "", []>;
 def SETB_C64r : I<0, Pseudo, (outs GR64:$dst), (ins), "", []>;
 } // isCodeGenOnly
 
-
-// Patterns to give priority when both inputs are zero so that we don't use
-// an immediate for the RHS.
-// TODO: Should we use a 32-bit sbb for 8/16 to push the extract_subreg out?
-def : Pat<(X86sbb_flag (i8 0), (i8 0), EFLAGS),
-          (SBB8rr (EXTRACT_SUBREG (MOV32r0), sub_8bit),
-                  (EXTRACT_SUBREG (MOV32r0), sub_8bit))>;
-def : Pat<(X86sbb_flag (i16 0), (i16 0), EFLAGS),
-          (SBB16rr (EXTRACT_SUBREG (MOV32r0), sub_16bit),
-                   (EXTRACT_SUBREG (MOV32r0), sub_16bit))>;
-def : Pat<(X86sbb_flag (i32 0), (i32 0), EFLAGS),
-          (SBB32rr (MOV32r0), (MOV32r0))>;
-def : Pat<(X86sbb_flag (i64 0), (i64 0), EFLAGS),
-          (SBB64rr (SUBREG_TO_REG (i64 0), (MOV32r0), sub_32bit),
-                   (SUBREG_TO_REG (i64 0), (MOV32r0), sub_32bit))>;
-
 //===----------------------------------------------------------------------===//
 // String Pseudo Instructions
 //

llvm/test/CodeGen/X86/shl-crash-on-legalize.ll

@@ -17,7 +17,7 @@ define i32 @PR29058(i8 %x, i32 %y) {
 ; CHECK-NEXT:    cmovnel %esi, %eax
 ; CHECK-NEXT:    xorl %edx, %edx
 ; CHECK-NEXT:    cmpb $1, %dil
-; CHECK-NEXT:    sbbb %dl, %dl
+; CHECK-NEXT:    sbbl %edx, %edx
 ; CHECK-NEXT:    orb %dl, %cl
 ; CHECK-NEXT:    # kill: def $cl killed $cl killed $ecx
 ; CHECK-NEXT:    shll %cl, %eax