[AArch64]: Add support for parsing rN registers.

Summary:
Allow rN registers to be simply parsed as correspoing xN registers.
The "register ... asm("rN")" is an command to the
compiler's register allocator, not an operand to any individual assembly
instruction. GCC documents this syntax as "...the name of the register
that should be used."

This is needed to support the changes in Linux kernel (see
https://lkml.org/lkml/2018/3/1/268 )

Note: This will add support only for the limited use case of
register ... asm("rN"). Any other uses that make rN leak into assembly
are not supported.

Reviewers: kristof.beyls, rengolin, peter.smith, t.p.northover

Reviewed By: peter.smith

Subscribers: javed.absar, eraman, cfe-commits, srhines

Differential Revision: https://reviews.llvm.org/D44815

llvm-svn: 328829

clang/lib/Basic/Targets/AArch64.cpp

@@ -308,7 +308,40 @@ ArrayRef<const char *> AArch64TargetInfo::getGCCRegNames() const {
 }
 
 const TargetInfo::GCCRegAlias AArch64TargetInfo::GCCRegAliases[] = {
-    {{"w31"}, "wsp"}, {{"x29"}, "fp"}, {{"x30"}, "lr"}, {{"x31"}, "sp"},
+    {{"w31"}, "wsp"},
+    {{"x31"}, "sp"},
+    // GCC rN registers are aliases of xN registers.
+    {{"r0"}, "x0"},
+    {{"r1"}, "x1"},
+    {{"r2"}, "x2"},
+    {{"r3"}, "x3"},
+    {{"r4"}, "x4"},
+    {{"r5"}, "x5"},
+    {{"r6"}, "x6"},
+    {{"r7"}, "x7"},
+    {{"r8"}, "x8"},
+    {{"r9"}, "x9"},
+    {{"r10"}, "x10"},
+    {{"r11"}, "x11"},
+    {{"r12"}, "x12"},
+    {{"r13"}, "x13"},
+    {{"r14"}, "x14"},
+    {{"r15"}, "x15"},
+    {{"r16"}, "x16"},
+    {{"r17"}, "x17"},
+    {{"r18"}, "x18"},
+    {{"r19"}, "x19"},
+    {{"r20"}, "x20"},
+    {{"r21"}, "x21"},
+    {{"r22"}, "x22"},
+    {{"r23"}, "x23"},
+    {{"r24"}, "x24"},
+    {{"r25"}, "x25"},
+    {{"r26"}, "x26"},
+    {{"r27"}, "x27"},
+    {{"r28"}, "x28"},
+    {{"r29", "x29"}, "fp"},
+    {{"r30", "x30"}, "lr"},
     // The S/D/Q and W/X registers overlap, but aren't really aliases; we
     // don't want to substitute one of these for a different-sized one.
 };

clang/test/CodeGen/aarch64-inline-asm.c

@@ -54,3 +54,23 @@ void test_constraint_Q(void) {
     asm("ldxr %0, %1" : "=r"(val) : "Q"(var));
 // CHECK: call i32 asm "ldxr $0, $1", "=r,*Q"(i64* @var)
 }
+
+void test_gcc_registers(void) {
+    register unsigned long reg0 asm("r0") = 0;
+    register unsigned long reg1 asm("r1") = 1;
+    register unsigned int  reg29 asm("r29") = 2;
+    register unsigned int  reg30 asm("r30") = 3;
+
+    // Test remapping register names in register ... asm("rN") statments.
+    // rN register operands in these two inline assembly lines
+    // should get renamed to valid AArch64 registers.
+    asm volatile("hvc #0" : : "r" (reg0), "r" (reg1));
+    // CHECK: call void asm sideeffect "hvc #0", "{x0},{x1}"
+    asm volatile("hvc #0" : : "r" (reg29), "r" (reg30));
+    // CHECK: call void asm sideeffect "hvc #0", "{fp},{lr}"
+
+    // rN registers when used without register ... asm("rN") syntax
+    // should not be remapped.
+    asm volatile("mov r0, r1\n");
+    // CHECK: call void asm sideeffect "mov r0, r1\0A", ""()
+}