MIPS/clang: Disallow constraint f for softfloat

Currently, clang accpets contraint f for softfloat, then
LLVM meet an internal error.

See: #64241

Author: wzssyqa

clang/lib/Basic/Targets/Mips.h

@@ -238,6 +238,9 @@ class LLVM_LIBRARY_VISIBILITY MipsTargetInfo : public TargetInfo {
     case 'd': // Equivalent to "r" unless generating MIPS16 code.
     case 'y': // Equivalent to "r", backward compatibility only.
     case 'f': // floating-point registers.
+      if (*Name == 'f' && FloatABI == SoftFloat)
+        return false;
+      LLVM_FALLTHROUGH;
     case 'c': // $25 for indirect jumps
     case 'l': // lo register
     case 'x': // hilo register pair

clang/test/Driver/mips-float.c

@@ -102,3 +102,17 @@
 // CHECK-ABI-SOFT-MIPS16: "-target-feature" "+mips16"
 // CHECK-ABI-SOFT-MIPS16: "-msoft-float"
 // CHECK-ABI-SOFT-MIPS16: "-mfloat-abi" "soft"
+
+/// On MIPS, don't accept constraint "f" for soft-float.
+// RUN: not %clang -S %s -o %t.s 2>&1 \
+// RUN:     -target mips-linux-gnu -msoft-float \
+// RUN:     -DSOFT_FLOAT_NO_CONSTRAINT_F \
+// RUN:   | FileCheck --check-prefix=CHECK-SOFTFLOAT-ASM-NO-F %s
+// CHECK-SOFTFLOAT-ASM-NO-F: error: invalid input constraint 'f' in asm
+
+#ifdef SOFT_FLOAT_NO_CONSTRAINT_F
+void read_float(float* p) {
+    float result = *p;
+    __asm__("" ::"f"(result));
+}
+#endif // SOFT_FLOAT_NO_CONSTRAINT_F