Fix stack address builtin for negative numbers

[zoecarver]

Summary

This patch checks that an argument passed to either of the builtins __builtin_frame_address or __builtin_return_address is at least 0. This patch resolves the issue where these builtins would cause an infinite loop ( 25497 ).

[zoecarver]

clang/test/Sema/builtin-stackaddress.c

10

For some reason lit was still erroring here.

[efriedma]

We usually prefer to generate error messages for incorrect parameters to builtins in SemaChecking.cpp.

I don't think there's really an infinite loop here. The parameter to __builtin_frame_address is an unsigned integer; values greater than 0x7FFFFFFU aren't special. The reason it takes a very long time is that we try to unroll the implied loop; generating an object file with four billion load instructions takes essentially forever. We could impose a smaller limit, but it would be sort of arbitrary.

[zoecarver]

Thanks for the explanation. Should I then not try to "fix" the issue? Or should I update sema checking?

[efriedma]

In the context of __builtin_frame_address, an arbitrary limit is probably okay. Maybe something like 0xFFFF, which is larger than anyone would realistically use, but doesn't take a crazy amount of time to compile.

[Jim]

I think this checking should be implemented in lib/Sema/SemaChecking.cpp.

[zoecarver]

@Jim Thanks, I'll move it.

[zoecarver]

• move verification to SemaChecking

[efriedma]

LGTM

[zoecarver]

Resolved by c93112dc4f745b0455addb54bfe1c2f79b827c6d

[zoecarver]

Reverted: 698078257285a044110620d7dab2fb4451a3fa29

[zoecarver]

• Error if SemaBuiltinConstantArgRange returns true, not false

[zoecarver]

I was using SemaBuiltinConstantArgRange incorrectly. I was returning an error for !SemaBuiltinConstantArgRange instead of SemaBuiltinConstantArgRange. Also, I only modified the fail tests so I wasn't able to catch the error. Updated and am running both the Sema and CodeGen tests now. Should fix the error.

[zoecarver]

• diff from master (arg phab...)

clang/test/Sema/builtin-stackaddress.c

 // RUN: %clang_cc1 -fsyntax-only -verify %s
 
-void a(unsigned x) {
+void* a(unsigned x) {
 return __builtin_return_address(0);
 }
 
 void b(unsigned x) {
 return __builtin_return_address(x); // expected-error{{argument to '__builtin_return_address' must be a constant integer}}
 }
 
 void* c(unsigned x) {
 // expected-error@+1 {{argument value 4294967295 is outside the valid range [0, 65535]}}
 return __builtin_return_address(-1);
 }
 
 void* d(unsigned x) {
 // expected-error@+1 {{argument value 1048575 is outside the valid range [0, 65535]}}
 return __builtin_return_address(0xFFFFF);