assigned to @nlewycky

I have verified that reverting back to 1.24 does not fix the bug.  It does, however, change the failure mode.

Hm. My problem is, I just did an llvm-gcc bootstrap build last night. It works
for me.

Of course, I'm running x86/linux, which is probably the major difference. What I
need here is a testcase. Do you have any other examples of code being
miscompiled by predsimplify? It would be much easier than trying to debug GCC.

Otherwise, someone's going to have to isolate the testcase out of gcc; compile
half the code with LLVM, half the code with GCC and link. See if the bug is
there, rinse & repeat. Getting it down to the .c file being miscompiled is good
enough for me.

Alternately, you could try narrowing down the optzns in predsimplify instead.
The major change from 1.23 and 1.24 was the workings of resolve. Try removing
the call to "resolve" from "addImpliedProperties". If the bug goes away, then
one of the transforms in resolve() is the culprit, otherwise it's either
addImpliedProperties or one of the Forwards::visit* methods.

If you can narrow it down for me, I can take it from there...

To be specific, when following the instructions, I get:

$ make install RC_OS=macos RC_ARCHS='i386 ppc' TARGETS='i386 ppc' SRCROOT=pwd
OBJROOT=pwd/build/obj DSTROOT=pwd/build/dst SYMROOT=pwd/build/sym
GNUmakefile:16: /CoreOS/Standard/Standard.make: No such file or directory
make: *** No rule to make target `/CoreOS/Standard/Standard.make'. Stop.

I reverted the predsimplifier back to 1.21.  Something in r1.22 broke it.  I don't follow the logic well
enough to understand what is going on.

-Chris

Chris, could you start with r1.24 and #if 0 away the code in case
Instruction:Xor and replace it with just "break;" ? Does that remove the problem?

Ok, I can reproduce this bug on x86/linux by running "make cleanstrap" (thanks
Chris for the clue). I'll try disabling parts of predsimplify until it works.

I've found and fixed a couple of miscompile bugs, but this bug remains.

It goes away if I remove the "case Instruction::Or" from addImpliedProperties. I
can further say that it's not caused by the bool type. What I'm doing now is
printing out a message when this optimization occurs. I'm going to use that to
narrow down the list of .c files that I need to binary search on.

Regardless, this is going to take a few days.

I have a predicate simplifier partial rewrite which fixes this problem. I'm
hoping to land the change this upcoming week.

Thanks for your patience...

New code has been checked in. I can bootstrap with predsimplify enabled. If you
can't, please reopen this bug.