[PATCH, i386]: Fix PR55929, unable to generate reloads for xbegin insn

[PATCH, i386]: Fix PR55929, unable to generate reloads for xbegin insn

[Uros Bizjak]

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Hello!

As mentioned by Andrew is PR, reload can't handle jump_insns. Expand
with %eax hard register temporary to avoid this limitation.

2012-01-10  Uros Bizjak  <ubizjak@gmail.com>

	PR target/55929
	* config/i386/i386.md (xbegin): Use %eax as a temporary register.

Bootstrapped and regression tested on x86_64-pc-linux-gnu {,-m32} and
by compiling libitm/beginend.cc preprocessed source with -Os mrtm
-std=gnu++0x. Committed to mainline SVN.

Uros.

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Index: config/i386/i386.md
===================================================================
--- config/i386/i386.md	(revision 195091)
+++ config/i386/i386.md	(working copy)
@@ -18013,19 +18013,22 @@
 
 (define_expand "xbegin"
   [(set (match_operand:SI 0 "register_operand")
-	(unspec_volatile:SI [(match_dup 1)] UNSPECV_XBEGIN))]
+	(unspec_volatile:SI [(const_int 0)] UNSPECV_XBEGIN))]
   "TARGET_RTM"
 {
   rtx label = gen_label_rtx ();
 
-  operands[1] = force_reg (SImode, constm1_rtx);
+  /* xbegin is emitted as jump_insn, so reload won't be able
+     to reload its operand.  Force the value into AX hard register.  */
+  rtx ax_reg = gen_rtx_REG (SImode, AX_REG);
+  emit_move_insn (ax_reg, constm1_rtx);
 
-  emit_jump_insn (gen_xbegin_1 (operands[1], label));
+  emit_jump_insn (gen_xbegin_1 (ax_reg, label));
 
   emit_label (label);
   LABEL_NUSES (label) = 1;
 
-  emit_move_insn (operands[0], operands[1]);
+  emit_move_insn (operands[0], ax_reg);
 
   DONE;
 })