1 files changed, 46 insertions, 0 deletions
diff --git a/llvm/lib/Target/X86/X86InstrCompiler.td b/llvm/lib/Target/X86/X86InstrCompiler.td
index 6ed62a00451..2c92cc370b5 100644
--- a/llvm/lib/Target/X86/X86InstrCompiler.td
+++ b/llvm/lib/Target/X86/X86InstrCompiler.td
@@ -737,6 +737,38 @@ defm LCMPXCHG8B : LCMPXCHG_UnOp<0xC7, MRM1m, "cmpxchg8b",
                                 IIC_CMPX_LOCK_8B>;
 }
 
+// This pseudo must be used when the frame uses RBX as
+// the base pointer. Indeed, in such situation RBX is a reserved
+// register and the register allocator will ignore any use/def of
+// it. In other words, the register will not fix the clobbering of
+// RBX that will happen when setting the arguments for the instrucion.
+// 
+// Unlike the actual related instuction, we mark that this one
+// defines EBX (instead of using EBX).
+// The rationale is that we will define RBX during the expansion of
+// the pseudo. The argument feeding EBX is ebx_input.
+//
+// The additional argument, $ebx_save, is a temporary register used to
+// save the value of RBX accross the actual instruction.
+//
+// To make sure the register assigned to $ebx_save does not interfere with
+// the definition of the actual instruction, we use a definition $dst which
+// is tied to $rbx_save. That way, the live-range of $rbx_save spans accross
+// the instruction and we are sure we will have a valid register to restore
+// the value of RBX.
+let Defs = [EAX, EDX, EBX, EFLAGS], Uses = [EAX, ECX, EDX],
+    SchedRW = [WriteALULd, WriteRMW], isCodeGenOnly = 1, isPseudo = 1,
+    Constraints = "$ebx_save = $dst", usesCustomInserter = 1 in {
+def LCMPXCHG8B_SAVE_EBX :
+    I<0, Pseudo, (outs GR32:$dst),
+      (ins i64mem:$ptr, GR32:$ebx_input, GR32:$ebx_save),
+      !strconcat("cmpxchg8b", "\t$ptr"),
+      [(set GR32:$dst, (X86cas8save_ebx addr:$ptr, GR32:$ebx_input,
+                                        GR32:$ebx_save))],
+      IIC_CMPX_LOCK_8B>;
+}
+
+
 let Defs = [RAX, RDX, EFLAGS], Uses = [RAX, RBX, RCX, RDX],
     Predicates = [HasCmpxchg16b], SchedRW = [WriteALULd, WriteRMW] in {
 defm LCMPXCHG16B : LCMPXCHG_UnOp<0xC7, MRM1m, "cmpxchg16b",
@@ -744,6 +776,20 @@ defm LCMPXCHG16B : LCMPXCHG_UnOp<0xC7, MRM1m, "cmpxchg16b",
                                  IIC_CMPX_LOCK_16B>, REX_W;
 }
 
+// Same as LCMPXCHG8B_SAVE_RBX but for the 16 Bytes variant.
+let Defs = [RAX, RDX, RBX, EFLAGS], Uses = [RAX, RCX, RDX],
+    Predicates = [HasCmpxchg16b], SchedRW = [WriteALULd, WriteRMW],
+    isCodeGenOnly = 1, isPseudo = 1, Constraints = "$rbx_save = $dst",
+    usesCustomInserter = 1 in {
+def LCMPXCHG16B_SAVE_RBX :
+    I<0, Pseudo, (outs GR64:$dst),
+      (ins i128mem:$ptr, GR64:$rbx_input, GR64:$rbx_save),
+      !strconcat("cmpxchg16b", "\t$ptr"),
+      [(set GR64:$dst, (X86cas16save_rbx addr:$ptr, GR64:$rbx_input,
+                                                    GR64:$rbx_save))],
+      IIC_CMPX_LOCK_16B>;
+}
+
 defm LCMPXCHG : LCMPXCHG_BinOp<0xB0, 0xB1, MRMDestMem, "cmpxchg",
                                X86cas, IIC_CMPX_LOCK_8, IIC_CMPX_LOCK>;