clang rejects valid character constants beginning with three backslashes

[efriedma-quic]

Bugzilla Link	4499
Resolution	FIXED
Resolved on	Jul 07, 2010 18:24
Version	unspecified
OS	Linux

Extended Description

Testcase:
int t1 = '\'';
int t2 = '\\';
int t3 = '\
';

All of these should be accepted (the first two are multi-character character constants).

Additional testcase:
int t4 = '\'; // Invalid, but currently prints a random
// large number of diagnostics

Issue found by code inspection.

[llvmbot]

The character constant lexer, Lexer::LexCharConstant, had a special case to handle the common case of a character constant like 'x' or '\y' efficiently.

But this shortcut broke the handling of multi-character constants starting with '\'.

Better to copy the code from Lexer::LexStringLiteral. The common case is just about as efficient as in the broken code.

In the case of 'x' and '\y' character literals, there is just one extra (unnecessary) char comparison. You could avoid this by using a do-while loop, but then you'd lose the symmetry with LexStringLiteral.

[llvmbot]

Test case and fix

[lattner]

Applied in r107836, thanks Kyle!