llvm-as mis-reads some negative integers

[asl]

Bugzilla Link	1245
Resolution	FIXED
Resolved on	Feb 22, 2010 12:46
Version	trunk
OS	Linux
Blocks	llvm/llvm-bugzilla-archive#1246
Attachments	failed .ll

Extended Description

Consider the attached .ll file.

Do:
llvm-as foo.ll -o - | ./llvm-dif -o foo-cmp.ll

I have (x86-linux):

....

•   %ov35 = add i32 %ov16, -29              ; <i32> [#uses=1]
  

•   %ov35 = add i32 %ov16, -93              ; <i32> [#uses=1]
    store i32 %ov35, i32* %state
    %pcc8 = add i32 %pcv7, 1                ; <i32> [#uses=1]
    store i32 %tmp20, i32* %tmp20_c
  

@@ -321,7 +321,7 @@
%ov7 = xor i32 %ov18_cc, 251 ; [#uses=3]
%ov41 = xor i32 %ov7, 116 ; [#uses=1]
%ov63 = sub i32 139, %ov7 ; [#uses=2]

•   %hvar68 = add i32 %ov63, -1             ; <i32> [#uses=1]
  

•   %hvar68 = add i32 %ov63, -9             ; <i32> [#uses=1]
  

and so on. Valgrind is quite. It's definitely an assembler bug, since output
binary code is broken.

[asl]

Note, that -93 is 0xFFF...FE3 and -29 is 0xFFFF...FA3. APInt issues?

[asl]

Err. Vice-versa. A3 and E3

[asl]

Well. The problem is definitely APInt issue. Let's look into {NInteger} rule in
the Lexer.l file. It correctly receives "-93" as yytext. But we have minBits = 6
and numBits = 7. After trunc we have "-29" as a value...

[asl]

One more addition. In any of such bad cases executing getSExtValue() before
trunc will result positive number. E.g.: +35 for "-93", "7 for "-9", +58 for
"-70". Funny, eh? :)

[llvmbot]

This is definitely a bug in APInt::getMinSignedBits(). For some values it is
off-by-one. I will fix this shortly.

[llvmbot]

This problem only affected negative integers whose "next to last" significant
bit was set. In such cases the number of bits computed as needed by the value
was off-by-one as it did not account for the sign bit. Consequently, the number
was parsed correctly by the "fromString" constructor but truncated to the wrong
length which changed the value.

This simple patch fixes it:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070305/045759.html

[asl]

mentioned in issue llvm/llvm-bugzilla-archive#1246