assigned to @lattner

This testcase may work better:

bool %nada(sbyte %X) {
%Y = cast sbyte %X to uint
%C = setgt uint %Y, 255
ret bool %C
}

Otherwise, instcombine will just delete all of the code. :)

In this case, it should be optimized to:

bool %nada(sbyte %X) {
%C = setlt sbyte %X, 0
ret bool %C
}

-Chris

Test Case Is Here:
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20041122/021393.html

Potential Patch
I've run through this numerous times and can't see anything wrong with it even
though it is substantially the same as the original.

Test Case
More rigorous test case

The "Potential Patch" produces the following xform from the "Test Case". I'd
appreciate it if you could review this and let me know if its okay to commit or
what I did wrong.

bool %lt_signed_to_large_unsigned(sbyte %SB) {
ret bool true
}
bool %lt_signed_to_large_signed(sbyte %SB) {
ret bool true
}
bool %lt_signed_to_large_negative(sbyte %SB) {
ret bool false
}
bool %lt_signed_to_small_unsigned(sbyte %SB) {
%C = setlt sbyte %SB, 17 ; [#uses=1]
ret bool %C
}
bool %lt_signed_to_small_signed(sbyte %SB) {
%C = setlt sbyte %SB, 17 ; [#uses=1]
ret bool %C
}
bool %lt_signed_to_small_negative(sbyte %SB) {
%C = setlt sbyte %SB, -17 ; [#uses=1]
ret bool %C
}
bool %lt_unsigned_to_large_unsigned(ubyte %SB) {
ret bool true
}
bool %lt_unsigned_to_large_signed(ubyte %SB) {
ret bool true
}
bool %lt_unsigned_to_large_negative(ubyte %SB) {
ret bool false
}
bool %lt_unsigned_to_small_unsigned(ubyte %SB) {
%C = setlt ubyte %SB, 17 ; [#uses=1]
ret bool %C
}
bool %lt_unsigned_to_small_signed(ubyte %SB) {
%C = setlt ubyte %SB, 17 ; [#uses=1]
ret bool %C
}
bool %lt_unsigned_to_small_negative(ubyte %SB) {
ret bool false
}
bool %gt_signed_to_large_unsigned(sbyte %SB) {
%C = setgt sbyte %SB, -127 ; [#uses=1]
ret bool %C
}
bool %gt_signed_to_large_signed(sbyte %SB) {
ret bool false
}
bool %gt_signed_to_large_negative(sbyte %SB) {
ret bool true
}
bool %gt_signed_to_small_unsigned(sbyte %SB) {
%C = setgt sbyte %SB, 17 ; [#uses=1]
ret bool %C
}
bool %gt_signed_to_small_signed(sbyte %SB) {
%C = setgt sbyte %SB, 17 ; [#uses=1]
ret bool %C
}
bool %gt_signed_to_small_negative(sbyte %SB) {
%C = setgt sbyte %SB, -17 ; [#uses=1]
ret bool %C
}
bool %gt_unsigned_to_large_unsigned(ubyte %SB) {
ret bool false
}
bool %gt_unsigned_to_large_signed(ubyte %SB) {
ret bool false
}
bool %gt_unsigned_to_large_negative(ubyte %SB) {
ret bool true
}
bool %gt_unsigned_to_small_unsigned(ubyte %SB) {
%C = setgt ubyte %SB, 17 ; [#uses=1]
ret bool %C
}
bool %gt_unsigned_to_small_signed(ubyte %SB) {
%C = setgt ubyte %SB, 17 ; [#uses=1]
ret bool %C
}
bool %gt_unsigned_to_small_negative(ubyte %SB) {
ret bool true
}

Second Potential Patch

Okay, the new patch now delivers:

bool %lt_signed_to_large_unsigned(sbyte %SB) {
ret bool true
}

bool %lt_signed_to_large_signed(sbyte %SB) {
ret bool true
}

bool %lt_signed_to_large_negative(sbyte %SB) {
ret bool false
}

bool %lt_signed_to_small_unsigned(sbyte %SB) {
%Y = cast sbyte %SB to ubyte ; [#uses=1]
%C = setlt ubyte %Y, 17 ; [#uses=1]
ret bool %C
}

bool %lt_signed_to_small_signed(sbyte %SB) {
%C = setlt sbyte %SB, 17 ; [#uses=1]
ret bool %C
}

bool %lt_signed_to_small_negative(sbyte %SB) {
%C = setlt sbyte %SB, -17 ; [#uses=1]
ret bool %C
}

bool %lt_unsigned_to_large_unsigned(ubyte %SB) {
ret bool true
}

bool %lt_unsigned_to_large_signed(ubyte %SB) {
ret bool true
}

bool %lt_unsigned_to_large_negative(ubyte %SB) {
ret bool false
}

bool %lt_unsigned_to_small_unsigned(ubyte %SB) {
%C = setlt ubyte %SB, 17 ; [#uses=1]
ret bool %C
}

bool %lt_unsigned_to_small_signed(ubyte %SB) {
%C = setlt ubyte %SB, 17 ; [#uses=1]
ret bool %C
}

bool %lt_unsigned_to_small_negative(ubyte %SB) {
ret bool false
}

bool %gt_signed_to_large_unsigned(sbyte %SB) {
%Y = cast sbyte %SB to ubyte ; [#uses=1]
%C = setgt ubyte %Y, 129 ; [#uses=1]
ret bool %C
}

bool %gt_signed_to_large_signed(sbyte %SB) {
ret bool false
}

bool %gt_signed_to_large_negative(sbyte %SB) {
ret bool true
}

bool %gt_signed_to_small_unsigned(sbyte %SB) {
%Y = cast sbyte %SB to ubyte ; [#uses=1]
%C = setgt ubyte %Y, 17 ; [#uses=1]
ret bool %C
}

bool %gt_signed_to_small_signed(sbyte %SB) {
%C = setgt sbyte %SB, 17 ; [#uses=1]
ret bool %C
}

bool %gt_signed_to_small_negative(sbyte %SB) {
%C = setgt sbyte %SB, -17 ; [#uses=1]
ret bool %C
}

bool %gt_unsigned_to_large_unsigned(ubyte %SB) {
ret bool false
}

bool %gt_unsigned_to_large_signed(ubyte %SB) {
ret bool false
}

bool %gt_unsigned_to_large_negative(ubyte %SB) {
ret bool true
}

bool %gt_unsigned_to_small_unsigned(ubyte %SB) {
%C = setgt ubyte %SB, 17 ; [#uses=1]
ret bool %C
}

bool %gt_unsigned_to_small_signed(ubyte %SB) {
%C = setgt ubyte %SB, 17 ; [#uses=1]
ret bool %C
}

bool %gt_unsigned_to_small_negative(ubyte %SB) {
ret bool true
}

Third Potential Patch
This is the same as the last one but it puts the guts of the Instruction::Cast
case of visitSetCondInst into visitSetCondInstWithCastAndConstant

The last patch is currently awaiting results of nightly testing. It will be
committed if it passes.

Resolution Patch Is Here:

http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20041122/021408.html

Part of this patch was disabled here:
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20050110/023419.html

It miscompiles the testcase in the commit.

-Chris

This transform was reimplemented and reenabled here:
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20050418/025735.html

-Chris

I just want to add a short note that the code contains several shifts in the
form "(1ULL << C2->getType()->getPrimitiveSizeInBits())-1;" which might cause
shift overflows.

Maybe it would be a good idea to implement some "uint64_t getHighBit(unsigned
bits)" and "uint64_t generateMask(unsigned bits)" helper functions that
correctly deal with bits == 64. Or these could also made member functions of Type.

Excellent point, I'll audit these.

Thanks!

-Chris

Yup, there were bugs. Fixed here:
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20050418/025751.html

Thanks!

-Chris