https://bugs.llvm.org/show_bug.cgi?id=33165
Bug ID: 33165
Summary: NewGVN miscompiles select undef
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Keywords: miscompilation
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
$ cat a.ll
define i2 @f(i2, i1) {
%a = xor i2 %0, -1
%b = select i1 %1, i2 %a, i2 undef
%c = and i2 %a, %b
ret i2 %c
}
$ opt -S a.ll -newgvn
define i2 @f(i2, i1) {
%a = xor i2 %0, -1
%b = select i1 %1, i2 %a, i2 undef
ret i2 %b
}
This is incorrect. Alive report:
ERROR: Mismatch in values of i2 ret_
Example:
%0 i2 = 0x2 (2, -2)
%1 i1 = 0x0 (0)
%a i2 = 0x1 (1)
%b i2 = 0x0 (0)
%c i2 = 0x0 (0)
Source value: 0x0 (0)
Target value: 0x2 (2, -2)
http://rise4fun.com/Alive/dKH
GVN gets this right (http://rise4fun.com/Alive/n6D):
$ opt -S a.ll -gvn
define i2 @f(i2, i1) {
%a = xor i2 %0, -1
ret i2 %a
}
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