Attached is a patch that adds a new parameter to limit the number
of SSA_NAME assignments for GCC to follow in iterative or recursive
algorithms. Purely as a proof of concept the patch introduces
the parameter into -Warray-bounds where the warning follows
POINTER_PLUS (and ASSERT_EXPR) assignments to get at the DECL
the final pointer points to.
With this "infrastructure" in place the parameter can start to be
introduced wherever else it might be necessary. I don't know of
any pathological cases where it actually is necessary (i.e., one
the 512 default keeps from going off the rails) so the test I have
put together for it is artificial. A better test case involving
one of the known recursive algorithms would be helpful.
Martin
gcc/ChangeLog:
* doc/invoke.texi (ssa-name-def-chain-limit): Document new --param.
* params.def (PARAM_SSA_NAME_DEF_CHAIN_LIMIT): Add new --param.
* tree-vrp.c (vrp_prop::check_mem_ref): Use
PARAM_SSA_NAME_DEF_CHAIN_LIMIT.
gcc/testsuite/ChangeLog:
* gcc.dg/Warray-bounds-43.c: New test.
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi (revision 273357)
+++ gcc/doc/invoke.texi (working copy)
@@ -12225,6 +12225,13 @@ before the loop versioning pass considers it too b
discounting any instructions in inner loops that directly benefit
from versioning.
+@item ssa-name-def-chain-limit
+The maximum number of SSA_NAME assignments to follow in determining
+a property of a variable such as its value. This limits the number
+of iterations or recursive calls GCC performs when optimizing certain
+statements or when determining their validity prior to issuing
+diagnostics.
+
@end table
@end table
Index: gcc/params.def
===================================================================
--- gcc/params.def (revision 273357)
+++ gcc/params.def (working copy)
@@ -1437,6 +1437,12 @@ DEFPARAM(PARAM_HASH_TABLE_VERIFICATION_LIMIT,
"each searched element.",
10, 0, 0)
+DEFPARAM(PARAM_SSA_NAME_DEF_CHAIN_LIMIT,
+ "ssa-name-def-chain-limit",
+ "The maximum number of SSA_NAME assignments to follow in determining "
+ "a value.",
+ 512, 0, 0)
+
/*
Local variables:
Index: gcc/tree-vrp.c
===================================================================
--- gcc/tree-vrp.c (revision 273357)
+++ gcc/tree-vrp.c (working copy)
@@ -4492,7 +4492,8 @@ vrp_prop::check_mem_ref (location_t location, tree
The loop computes the range of the final offset for expressions such
as (A + i0 + ... + iN)[CSTOFF] where i0 through iN are SSA_NAMEs in
some range. */
- while (TREE_CODE (arg) == SSA_NAME)
+ const unsigned limit = PARAM_VALUE (PARAM_SSA_NAME_DEF_CHAIN_LIMIT);
+ for (unsigned n = 0; TREE_CODE (arg) == SSA_NAME && n < limit; ++n)
{
gimple *def = SSA_NAME_DEF_STMT (arg);
if (!is_gimple_assign (def))
Index: gcc/testsuite/gcc.dg/Warray-bounds-43.c
===================================================================
--- gcc/testsuite/gcc.dg/Warray-bounds-43.c (nonexistent)
+++ gcc/testsuite/gcc.dg/Warray-bounds-43.c (working copy)
@@ -0,0 +1,133 @@
+/* Test to verify that --param ssa_name_def_chain_limit can be used to
+ limit the maximum number of SSA_NAME assignments the warning follows.
+ { dg-do compile }
+ { dg-options "-O2 -Wall --param ssa-name-def-chain-limit=4" } */
+
+#define NOIPA __attribute__ ((noipa))
+
+const char a0[] = "";
+const char a1[] = "1";
+const char a2[] = "12";
+const char a3[] = "123";
+const char a4[] = "1234";
+const char a5[] = "12345";
+const char a6[] = "123456";
+const char a7[] = "1234567";
+const char a8[] = "12345678";
+const char a9[] = "123456789";
+
+void f (const char*, ...);
+
+int i0, i1, i2, i3, i4, i5, i6, i7, i8;
+
+NOIPA int g2 (int i)
+{
+ if (i < 1) i = 1;
+
+ const char *p0 = a9;
+ const char *p1 = p0 + i;
+ const char *p2 = p1 + i;
+
+ f (p0, p1, p2);
+
+ return p2[8]; // { dg-warning "\\\[-Warray-bounds]" }
+}
+
+NOIPA int g3 (int i)
+{
+ if (i < 1) i = 1;
+
+ const char *p0 = a9;
+ const char *p1 = p0 + i;
+ const char *p2 = p1 + i;
+ const char *p3 = p2 + i;
+
+ f (p0, p1, p2, p3);
+
+ return p3[7]; // { dg-warning "\\\[-Warray-bounds]" }
+}
+
+NOIPA int g4 (int i)
+{
+ if (i < 1) i = 1;
+
+ const char *p0 = a9;
+ const char *p1 = p0 + i;
+ const char *p2 = p1 + i;
+ const char *p3 = p2 + i;
+ const char *p4 = p3 + i;
+
+ f (p0, p1, p2, p3, p4);
+
+ return p4[6]; // { dg-warning "\\\[-Warray-bounds]" }
+}
+
+NOIPA int g5 (int i)
+{
+ if (i < 1) i = 1;
+
+ const char *p0 = a9;
+ const char *p1 = p0 + i;
+ const char *p2 = p1 + i;
+ const char *p3 = p2 + i;
+ const char *p4 = p3 + i;
+ const char *p5 = p4 + i;
+
+ f (p0, p1, p2, p3, p4, p5);
+
+ return p5[5];
+}
+
+NOIPA int g6 (int i)
+{
+ if (i < 1) i = 1;
+
+ const char *p0 = a9;
+ const char *p1 = p0 + i;
+ const char *p2 = p1 + i;
+ const char *p3 = p2 + i;
+ const char *p4 = p3 + i;
+ const char *p5 = p4 + i;
+ const char *p6 = p5 + i;
+
+ f (p0, p1, p2, p3, p4, p5, p6);
+
+ return p6[4];
+}
+
+NOIPA int g7 (int i)
+{
+ if (i < 1) i = 1;
+
+ const char *p0 = a9;
+ const char *p1 = p0 + i;
+ const char *p2 = p1 + i;
+ const char *p3 = p2 + i;
+ const char *p4 = p3 + i;
+ const char *p5 = p4 + i;
+ const char *p6 = p5 + i;
+ const char *p7 = p6 + i;
+
+ f (p0, p1, p2, p3, p4, p5, p6, p7);
+
+ return p7[3];
+}
+
+NOIPA int g8 (int i)
+{
+ if (i < 1) i = 1;
+
+ const char *p0 = a9;
+ const char *p1 = p0 + i;
+ const char *p2 = p1 + i;
+ const char *p3 = p2 + i;
+ const char *p4 = p3 + i;
+ const char *p5 = p4 + i;
+ const char *p6 = p5 + i;
+ const char *p7 = p6 + i;
+ const char *p8 = p7 + i;
+
+ f (p0, p1, p2, p3, p4, p5, p6, p7, p8);
+
+ return p8[2];
+}
