https://llvm.org/bugs/show_bug.cgi?id=27506
Bug ID: 27506
Summary: GVN's propagateEquality propagates wrong equality
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: kyoo...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Created attachment 16264
--> https://llvm.org/bugs/attachment.cgi?id=16264&action=edit
llvm code that exposes error
GVN's `propagateEquality` propagates wrong equality related to icmp
instructions.
When it propagates such as "(icmp eq A B) == true", it also propagates "A ==
B". However, this may cause an incorrect behavior if either A or B is an
undefined value.
When the source code like below is given, GVN transforms the "b1" block as
shown. Suppose %x has a normal value and %u has the undef value. In the source,
"%aa" is always defined. However, in the target, "%aa" is replaced with "%u",
which is undef.
We attach an input llvm file of "opt -gvn" and a C example code that exposes
the same problem when compiled using "clang -O2". We tested this in both clang
3.7.1 and the trunk.
b0:
%a = add i32 %x, 1
%c = icmp eq i32 %a, %u
br i1 %c, label %b1, label %b2
b1:
%aa = add i32 %x, 1
%d = call i32 @bar(i32 %aa)
->
b1:
%d = call i32 @bar(i32 %u)
--
You are receiving this mail because:
You are on the CC list for the bug.
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
