[cfe-dev] Patch to correctly determine when the address of a compound expression is constant

[Eli Friedman]

>From http://llvm.org/bugs/show_bug.cgi?id=1891; patch at
http://llvm.org/bugs/attachment.cgi?id=1318, and also attached (I
don't know if GMail will mangle it...).

Patch fixes testcases like:
static int *p = (int []){2, 4};

and

typedef struct Test {int a;int b;} Test;
static Test* ll = &(Test) {0,0};

so that they get through sema correctly.

This patch fixes a few underlying issues:

1. It was previously not possible to determine (AFAIK) whether a
CompoundLiteralExpr was file scope or not, so this patch propagates
that information from the parser.  This is the biggest change, but is
mostly mechanical.
2. It makes Expr::hasStaticStorage use that information when necessary.
3. It makes Expr::isConstantExpr deal with arrays that aren't
declarations (currently, that's just compound literals).
4. It changes the order of the checks in Sema::CheckSingleInitializer
so that any necessary implicit casts get added before checking for
whether an initializer is constant.

Expr::isConstantExpr definitely needs more work; it is currently
letting through some expressions that aren't constant, like:
static int r[2] = {1,2};
static int ss[2] = {3,4};
static int t = r-ss; // Wrong: Illegal per C99, and impossible to emit to LLVM
static int* zz = &r[t]; // Wrong: Obviously not constant

Expr::hasStaticStorage and Expr::isConstantExpr probably need to be
restructured to deal with cases like &r[t];

-Eli Friedman
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