[PATCH] rs6000: Add "cannot_copy" attribute, use it (PR67788, PR67789)

[Segher Boessenkool <segher at kernel dot crashing dot org>]

After the shrink-wrapping patches the prologue will often be pushed
"deeper" into the function, which in turn means the software trace cache
pass will more often want to duplicate the basic block containing the
prologue.  This caused failures for 32-bit SVR4 with -msecure-plt PIC.

This configuration uses the load_toc_v4_PIC_1 instruction, which creates
assembler labels without using the normal machinery for that.  If now
the compiler decides to duplicate the insn, it will emit the same label
twice.  Boom.

It isn't so easy to fix this to use labels the compiler knows about (let
alone test that properly).  Instead, this patch wires up a "cannot_copy"
attribute to be used by TARGET_CANNOT_COPY_P, and sets that attribute on
these insns we do not want copied.

Bootstrapped and tested on powerpc64-linux, with the usual configurations
(-m32,-m32/-mpowerpc64,-m64,-m64/-mlra); new testcase fails before, works
after (on 32-bit).

Is this okay for mainline?


Segher


2015-09-30  Segher Boessenkool  <segher@kernel.crashing.org>

	PR target/67788
	PR target/67789
	* config/rs6000/rs6000.c (TARGET_CANNOT_COPY_INSN_P): New.
	(rs6000_cannot_copy_insn_p): New function.
	* config/rs6000/rs6000.md (cannot_copy): New attribute.
	(load_toc_v4_PIC_1_normal): Set cannot_copy.
	(load_toc_v4_PIC_1_476): Ditto.

gcc/testsuite/
	PR target/67788
	PR target/67789
	* gcc.target/powerpc/pr67789.c: New testcase.

---
 gcc/config/rs6000/rs6000.c                 | 11 +++++++++
 gcc/config/rs6000/rs6000.md                |  9 +++++--
 gcc/testsuite/gcc.target/powerpc/pr67789.c | 39 ++++++++++++++++++++++++++++++
 3 files changed, 57 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/powerpc/pr67789.c

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 93bb725..29fd198 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -1513,6 +1513,8 @@ static const struct attribute_spec rs6000_attribute_table[] =
 #define TARGET_REGISTER_MOVE_COST rs6000_register_move_cost
 #undef TARGET_MEMORY_MOVE_COST
 #define TARGET_MEMORY_MOVE_COST rs6000_memory_move_cost
+#undef TARGET_CANNOT_COPY_INSN_P
+#define TARGET_CANNOT_COPY_INSN_P rs6000_cannot_copy_insn_p
 #undef TARGET_RTX_COSTS
 #define TARGET_RTX_COSTS rs6000_rtx_costs
 #undef TARGET_ADDRESS_COST
@@ -31226,6 +31228,15 @@ rs6000_xcoff_encode_section_info (tree decl, rtx rtl, int first)
 #endif /* HAVE_AS_TLS */
 #endif /* TARGET_XCOFF */
 
+/* Return true if INSN should not be copied.  */
+
+static bool
+rs6000_cannot_copy_insn_p (rtx_insn *insn)
+{
+  return recog_memoized (insn) >= 0
+	 && get_attr_cannot_copy (insn);
+}
+
 /* Compute a (partial) cost for rtx X.  Return true if the complete
    cost has been computed, and false if subexpressions should be
    scanned.  In either case, *TOTAL contains the cost result.  */
diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
index cfdb286..8c53c40 100644
--- a/gcc/config/rs6000/rs6000.md
+++ b/gcc/config/rs6000/rs6000.md
@@ -226,6 +226,9 @@ (define_attr "var_shift" "no,yes"
 			      (const_string "no"))
 		(const_string "no")))
 
+;; Is copying of this instruction disallowed?
+(define_attr "cannot_copy" "no,yes" (const_string "no"))
+
 ;; Define floating point instruction sub-types for use with Xfpu.md
 (define_attr "fp_type" "fp_default,fp_addsub_s,fp_addsub_d,fp_mul_s,fp_mul_d,fp_div_s,fp_div_d,fp_maddsub_s,fp_maddsub_d,fp_sqrt_s,fp_sqrt_d" (const_string "fp_default"))
 
@@ -9130,7 +9133,8 @@ (define_insn "load_toc_v4_PIC_1_normal"
    && (flag_pic == 2 || (flag_pic && TARGET_SECURE_PLT))"
   "bcl 20,31,%0\\n%0:"
   [(set_attr "type" "branch")
-   (set_attr "length" "4")])
+   (set_attr "length" "4")
+   (set_attr "cannot_copy" "yes")])
 
 (define_insn "load_toc_v4_PIC_1_476"
   [(set (reg:SI LR_REGNO)
@@ -9148,7 +9152,8 @@ (define_insn "load_toc_v4_PIC_1_476"
   return templ;
 }"
   [(set_attr "type" "branch")
-   (set_attr "length" "4")])
+   (set_attr "length" "4")
+   (set_attr "cannot_copy" "yes")])
 
 (define_expand "load_toc_v4_PIC_1b"
   [(parallel [(set (reg:SI LR_REGNO)
diff --git a/gcc/testsuite/gcc.target/powerpc/pr67789.c b/gcc/testsuite/gcc.target/powerpc/pr67789.c
new file mode 100644
index 0000000..d1bd047
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr67789.c
@@ -0,0 +1,39 @@
+/* { dg-do assemble } */
+/* { dg-options "-O2 -msecure-plt -fPIC" } */
+
+#define FE_TONEAREST 0
+#define FE_UPWARD 1
+#define FE_DOWNWARD 2
+#define FE_TOWARDZERO 3
+
+extern int fesetround(int);
+
+void
+set_fpu_rounding_mode (int mode)
+{
+  int rnd_mode;
+
+  switch (mode)
+    {
+      case 2:
+       rnd_mode = FE_TONEAREST;
+       break;
+
+      case 4:
+        rnd_mode = FE_UPWARD;
+        break;
+
+      case 1:
+        rnd_mode = FE_DOWNWARD;
+        break;
+
+      case 3:
+        rnd_mode = FE_TOWARDZERO; 
+        break;
+
+      default:
+        return;
+    }
+
+  fesetround (rnd_mode);
+}
-- 
1.8.1.4