[Clang][LoongArch] Support inline asm constraint 'J'

'J' is defined in GCC [1] but not documented [2] while Linux [3] has
already used it in LoongArch port.

[1]: https://github.com/gcc-mirror/gcc/blob/master/gcc/config/loongarch/constraints.md#L61
[2]: https://gcc.gnu.org/onlinedocs/gccint/Machine-Constraints.html
[3]: https://github.com/torvalds/linux/blob/master/arch/loongarch/include/asm/cmpxchg.h#L19

Differential Revision: https://reviews.llvm.org/D136835

Author: SixWeining

clang/lib/Basic/Targets/LoongArch.cpp

@@ -88,6 +88,10 @@ bool LoongArchTargetInfo::validateAsmConstraint(
     // A signed 12-bit constant (for arithmetic instructions).
     Info.setRequiresImmediate(-2048, 2047);
     return true;
+  case 'J':
+    // Integer zero.
+    Info.setRequiresImmediate(0);
+    return true;
   case 'K':
     // An unsigned 12-bit constant (for logic instructions).
     Info.setRequiresImmediate(0, 4095);

clang/test/CodeGen/LoongArch/inline-asm-constraints.c

@@ -43,6 +43,12 @@ void test_I(void) {
   asm volatile ("" :: "I"(-2048));
 }
 
+void test_J(void) {
+// CHECK-LABEL: define{{.*}} void @test_J()
+// CHECK: call void asm sideeffect "", "J"(i32 0)
+  asm volatile ("" :: "J"(0));
+}
+
 void test_K(void) {
 // CHECK-LABEL: define{{.*}} void @test_K()
 // CHECK: call void asm sideeffect "", "K"(i32 4095)

llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp

@@ -2184,6 +2184,7 @@ LoongArchTargetLowering::getConstraintType(StringRef Constraint) const {
   //       offset that is suitable for use in instructions with the same
   //       addressing mode as st.w and ld.w.
   // 'I':  A signed 12-bit constant (for arithmetic instructions).
+  // 'J':  Integer zero.
   // 'K':  An unsigned 12-bit constant (for logic instructions).
   // "ZB": An address that is held in a general-purpose register. The offset is
   //       zero.
@@ -2198,6 +2199,7 @@ LoongArchTargetLowering::getConstraintType(StringRef Constraint) const {
       return C_RegisterClass;
     case 'l':
     case 'I':
+    case 'J':
     case 'K':
       return C_Immediate;
     case 'k':
@@ -2301,6 +2303,13 @@ void LoongArchTargetLowering::LowerAsmOperandForConstraint(
               DAG.getTargetConstant(CVal, SDLoc(Op), Subtarget.getGRLenVT()));
       }
       return;
+    case 'J':
+      // Validate & create an integer zero operand.
+      if (auto *C = dyn_cast<ConstantSDNode>(Op))
+        if (C->getZExtValue() == 0)
+          Ops.push_back(
+              DAG.getTargetConstant(0, SDLoc(Op), Subtarget.getGRLenVT()));
+      return;
     case 'K':
       // Validate & create a 12-bit unsigned immediate operand.
       if (auto *C = dyn_cast<ConstantSDNode>(Op)) {

llvm/test/CodeGen/LoongArch/inline-asm-constraint-error.ll

@@ -17,6 +17,12 @@ define void @constraint_I() {
   ret void
 }
 
+define void @constraint_J() {
+; CHECK: error: value out of range for constraint 'J'
+  tail call void asm sideeffect "addi.w $$a0, $$a0, $$0", "J"(i32 1)
+  ret void
+}
+
 define void @constraint_K() {
 ; CHECK: error: value out of range for constraint 'K'
   tail call void asm sideeffect "andi.w $$a0, $$a0, $0", "K"(i32 4096)

llvm/test/CodeGen/LoongArch/inline-asm-constraint.ll

@@ -58,6 +58,17 @@ define void @constraint_I() nounwind {
   ret void
 }
 
+define void @constraint_J() nounwind {
+; CHECK-LABEL: constraint_J:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    addi.w $a0, $a0, 0
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    ret
+  tail call void asm sideeffect "addi.w $$a0, $$a0, $0", "J"(i32 0)
+  ret void
+}
+
 define void @constraint_K() nounwind {
 ; CHECK-LABEL: constraint_K:
 ; CHECK:       # %bb.0: