Trunk miscompiles libjava

[Andrew Haley]

Boehm, Hans writes:
 > On Linux/IA64, and probably other platforms, the trunk gcc miscompiles the isWhiteSpace() method in libjava/java/lang/Character.  Apparently the bit-wise & in a return is the problem.  This is a regression from 3.1.  It fails with the current CVS and failed with the one from a few days ago.
 > 
 > Reduced test case (only isWhitespace is miscompiled, the rest is scaffolding):
 > 
 > class mychar {
 >   public static boolean isWhitespace(char ch)
 >   {
 >     int attr = readChar(ch);
 >     return (((1 << attr) & 0x7000) != 0);
 >   }
 > 
 > 
 >   private static char readChar(char ch) {
 >     if (ch < 128) return (char) 9;
 >     return 9999;
 >   }
 > 
 >   public static void main(String[] argv) {
 >     if (isWhitespace('4'))
 >       System.out.println("FAIL 1");
 >     if (isWhitespace('a'))
 >       System.out.println("FAIL 2");
 >   }
 > }
 > 
 > Offending RTL instruction (partial diff of trunk (-) against 3.1 output (+)):
 > 
 >  (insn 57 56 59 (set (reg:DI 359)
 > -        (zero_extend:DI (subreg:QI (reg:SI 355) 0))) -1 (nil)
 > +        (and:DI (subreg:DI (reg:SI 355) 0)
 > +            (const_int 1 [0x1]))) -1 (nil)
 >      (nil))
 >  
 > In both 3.1 and the trunk, the code in the return is compiled as a
 > variable right shift of 0x7000.  In the 3.1 version, this is anded
 > against 0x1.  In the trunk version the and is dropped.

It's the old problem that bites us all the time.  fold() is doing
conversions that are legal C but not legal java.

It's caused by this patch:

revision 1.195
date: 2002/04/18 10:39:20;  author: jakub;  state: Exp;  lines: +43 -0
	* fold-const.c (fold) [NOP_EXPR]: Convert (T)(x&c) into ((T)x&(T)c)
	for integer constant c (if x has unsigned type or sign bit is not
	set in c).  This folds the zero/sign extension into the bit-wise and
	operation.

	* gcc.c-torture/compile/20020415-1.c: New.

I don't think there's anything wrong with this patch, but it causes
breakage on systems that have a boolean type smaller than int.

I intend to dig deeper tomorrow.

Andrew.