[RISCV] Add inline asm constraints I, J & K for RISC-V

This allows the constraints I, J & K to be used in inline asm for
RISC-V, with the following semantics (equivalent to GCC):

I: Any 12-bit signed immediate.
J: Integer zero only.
K: Any 5-bit unsigned immediate.

See the GCC definitions here:
https://gcc.gnu.org/onlinedocs/gccint/Machine-Constraints.html

Differential Revision: https://reviews.llvm.org/D54091

llvm-svn: 363055

Author: lewis-revill

clang/lib/Basic/Targets/RISCV.cpp

@@ -39,6 +39,26 @@ ArrayRef<TargetInfo::GCCRegAlias> RISCVTargetInfo::getGCCRegAliases() const {
   return llvm::makeArrayRef(GCCRegAliases);
 }
 
+bool RISCVTargetInfo::validateAsmConstraint(
+    const char *&Name, TargetInfo::ConstraintInfo &Info) const {
+  switch (*Name) {
+  default:
+    return false;
+  case 'I':
+    // A 12-bit signed immediate.
+    Info.setRequiresImmediate(-2048, 2047);
+    return true;
+  case 'J':
+    // Integer zero.
+    Info.setRequiresImmediate(0);
+    return true;
+  case 'K':
+    // A 5-bit unsigned immediate for CSR access instructions.
+    Info.setRequiresImmediate(0, 31);
+    return true;
+  }
+}
+
 void RISCVTargetInfo::getTargetDefines(const LangOptions &Opts,
                                        MacroBuilder &Builder) const {
   Builder.defineMacro("__ELF__");

clang/lib/Basic/Targets/RISCV.h

@@ -61,9 +61,7 @@ class RISCVTargetInfo : public TargetInfo {
   ArrayRef<TargetInfo::GCCRegAlias> getGCCRegAliases() const override;
 
   bool validateAsmConstraint(const char *&Name,
-                             TargetInfo::ConstraintInfo &Info) const override {
-    return false;
-  }
+                             TargetInfo::ConstraintInfo &Info) const override;
 
   bool hasFeature(StringRef Feature) const override;