llvm-gcc fails to infer a constant expr involving static ptr is also constant

[llvmbot]

Bugzilla Link	115
Resolution	FIXED
Resolved on	Feb 22, 2010 12:50
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor

Extended Description

I think both "xend"s, below, should compile to the same thing (except, of
course, for the fact that they refer to different "x"s), which is what happens
in native gcc 3.3. Instead, the 2nd one, in "bar", gives us an error, as shown.
bar() is reduced from a function in f2c.

194 gally>
/home/vadve/lattner/local/x86/llvm-gcc/libexec/gcc/i686-pc-linux-gnu/3.4-llvm/cc1
-quiet foo.i
foo.i: In function `bar':

foo.i:8: error: initializer element is not constant
195 gally> cat foo.i
void foo () {
static char x[10];
static char *xend = &x[10];
}

void bar () {
static char x[10];
static char *xend = x + 10;
}

[llvmbot]

assigned to @lattner

[lattner]

You're right, this is a bug. This was caused by some of the type-safety fixes I
put in. I'll fix it tommorow. This is a regression from 1.0.

-Chris

[lattner]

This bug was caused by the fix to Bug 84, so it was not present in 1.0.

The test is: test/Regression/CFrontend/2003-11-16-StaticArrayInit.c
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20031110/009563.html

Fixed like this:

$ diff -u c-common.c~ c-common.c
--- c-common.c~ Thu Nov 13 01:08:20 2003
+++ c-common.c Sun Nov 16 14:45:22 2003
@@ -2528,7 +2528,8 @@
intop = convert (c_common_type_for_size (TYPE_PRECISION (sizetype),
TREE_UNSIGNED (sizetype)), intop);

• if (EMIT_LLVM) {

• /* Don't create an ARRAY_REF if this is a potentially a static initializer. */
• if (EMIT_LLVM && (!TREE_CONSTANT (ptrop) || !TREE_CONSTANT(intop))) {
  /* In LLVM we really want to represent this as &P[i], not as P+i*sizeof(*P)
  */
  tree arrayref;

-Chris