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RFA: Tighten checking for 'X' constraints
- From: Richard Sandiford <rdsandiford at googlemail dot com>
- To: gcc-patches at gcc dot gnu dot org
- Cc: Robert Suchanek <Robert dot Suchanek at imgtec dot com>
- Date: Tue, 15 Apr 2014 21:53:16 +0100
- Subject: RFA: Tighten checking for 'X' constraints
- Authentication-results: sourceware.org; auth=none
As Robert pointed out here:
http://gcc.gnu.org/ml/gcc-patches/2014-04/msg00416.html
we're a bit too eager when folding stuff into an 'X' constraint.
The value at expand time is sensible, but after that asm_operand_ok
allows arbitrary rtx expressions, including any number of registers
as well as MEMs with unchecked addresses.
This is a target-independent problem, as shown by the testcase below.
Reload would give bogus "impossible constraint in asm" errors
while LRA ICEs.
Tested on x86_64-linux-gnu. OK to install?
Thanks,
Richard
gcc/
* recog.c (asm_operand_ok): Tighten MEM validity for 'X'.
gcc/testsuite/
* gcc.dg/torture/asm-x-constraint-1.c: New test.
Index: gcc/recog.c
===================================================================
--- gcc/recog.c 2014-04-12 22:43:54.729854903 +0100
+++ gcc/recog.c 2014-04-15 21:47:32.139873570 +0100
@@ -1840,7 +1840,17 @@ asm_operand_ok (rtx op, const char *cons
break;
case 'X':
- result = 1;
+ /* Although the asm itself doesn't impose any restrictions on
+ the operand, we still need to restrict it to something that
+ can be reloaded and printed.
+
+ MEM operands are always reloaded to make them legitimate,
+ regardless of the constraint, so we need to handle them
+ in the same way as for 'm' and 'g'. Since 'X' is not treated
+ as an address constraint, the only other valid operand types
+ are constants and registers. */
+ result = (CONSTANT_P (op)
+ || general_operand (op, VOIDmode));
break;
case 'g':
Index: gcc/testsuite/gcc.dg/torture/asm-x-constraint-1.c
===================================================================
--- /dev/null 2014-04-15 08:10:27.294524132 +0100
+++ gcc/testsuite/gcc.dg/torture/asm-x-constraint-1.c 2014-04-15 19:11:29.830962008 +0100
@@ -0,0 +1,27 @@
+void
+noprop1 (int **x, int y, int z)
+{
+ int *ptr = *x + y * z / 11;
+ __asm__ __volatile__ ("noprop1 %0" : : "X" (*ptr));
+}
+
+void
+noprop2 (int **x, int y, int z)
+{
+ int *ptr = *x + y * z / 11;
+ __asm__ __volatile__ ("noprop2 %0" : : "X" (ptr));
+}
+
+int *global_var;
+
+void
+const1 (void)
+{
+ __asm__ __volatile__ ("const1 %0" : : "X" (global_var));
+}
+
+void
+const2 (void)
+{
+ __asm__ __volatile__ ("const2 %0" : : "X" (*global_var));
+}