[mips] Add support for 'ZC' inline assembly memory constraint.

[dsanders]

Summary

Also add tests for 'R' and 'm'.

[atanasyan]

lib/Basic/Targets.cpp

5941

What does return this function if 'Z' is not followed by 'C'?

case 'Z':
  if (Name[1] != 'C')
    return false;
  Info.setAllowsMemory();
  Name++; // Skip over 'Z'.
  return true;

[dsanders]

lib/Basic/Targets.cpp

5941

It's supposed to return false. I'll fix it shortly.

[dsanders]

Fix missing return.

[atanasyan]

LGTM

lib/Basic/Targets.cpp

bool validateAsmConstraint(const char *&Name,
     case 'M': // Constants not loadable via lui, addiu, or ori
     case 'N': // Constant -1 to -65535
     case 'O': // A signed 15-bit constant
     case 'P': // A constant between 1 go 65535
       return true;
     case 'R': // An address that can be used in a non-macro load or store
       Info.setAllowsMemory();
       return true;
+    case 'Z':
+      if (Name[1] == 'C') { // An address usable by ll, and sc.
+        Info.setAllowsMemory();
+        Name++; // Skip over 'Z'.
+        return true;
+      }
+      return false;
+    }
+  }
+
+  std::string convertConstraint(const char *&Constraint) const override {
+    std::string R;
+    switch (*Constraint) {
+    case 'Z': // Two-character constraint; add "^" hint for later parsing.
+      if (Constraint[1] == 'C') {
+        R = std::string("^") + std::string(Constraint, 2);
+        Constraint++;
+        return R;
+      }
+      break;
     }
+    return TargetInfo::convertConstraint(Constraint);
   }
 
   const char *getClobbers() const override {
     // In GCC, $1 is not widely used in generated code (it's used only in a few
     // specific situations), so there is no real need for users to add it to
     // the clobbers list if they want to use it in their inline assembly code.
     //
     // In LLVM, $1 is treated as a normal GPR and is always allocatable during

test/CodeGen/mips-inline-asm.c

+// REQUIRES: mips-registered-target
+// RUN: %clang_cc1 -triple mips-linux-gnu -emit-llvm -o - %s | FileCheck %s
+
+int data;
+
+void m () {
+  asm("lw $1, %0" :: "m"(data));
+  // CHECK: call void asm sideeffect "lw $$1, $0", "*m,~{$1}"(i32* @data)
+}
+
+void ZC () {
+  asm("ll $1, %0" :: "ZC"(data));
+  // CHECK: call void asm sideeffect "ll $$1, $0", "*^ZC,~{$1}"(i32* @data)
+}
+
+void R () {
+  asm("lw $1, %0" :: "R"(data));
+  // CHECK: call void asm sideeffect "lw $$1, $0", "*R,~{$1}"(i32* @data)
+}