https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79594
Bug ID: 79594
Summary: -Waggressive-loop-optimizations incomplete and/or
inconsistentt
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vincenzo.innocente at cern dot ch
Target Milestone: ---
given
cat aggressiveLoop.cc
#include <cmath>
#include<limits>
float x[1024];
float y[1024];
float w[512];
float z[128];
float c,q;
void foo() {
for (int i=0; i<1024; ++i) {
auto zz=z[i];
auto yy = y[i];
if(x[i] > q) yy = zz;
y[i]=yy;
}
}
void foo2() {
for (int i=0; i<1024; ++i) {
auto zz=z[i];
auto yy = w[i];
if(x[i] > q) yy = zz;
x[i]=yy;
}
}
void foo3() {
for (int i=0; i<1024; ++i) {
auto zz=z[i];
auto yy = w[i];
if(x[i] > q) yy = zz;
w[i]=yy;
}
}
gcc version 7.0.1 20170205 (experimental) [trunk revision 245191] (GCC)
reports
c++ -Wall -O2 aggressiveLoop.cc -S
aggressiveLoop.cc: In function 'void foo()':
aggressiveLoop.cc:13:9: warning: iteration 128 invokes undefined behavior
[-Waggressive-loop-optimizations]
auto zz=z[i];
^~
aggressiveLoop.cc:12:18: note: within this loop
for (int i=0; i<1024; ++i) {
~^~~~~
aggressiveLoop.cc: In function 'void foo2()':
aggressiveLoop.cc:22:9: warning: iteration 128 invokes undefined behavior
[-Waggressive-loop-optimizations]
auto zz=z[i];
^~
aggressiveLoop.cc:21:18: note: within this loop
for (int i=0; i<1024; ++i) {
~^~~~~
aggressiveLoop.cc: In function 'void foo3()':
aggressiveLoop.cc:34:8: warning: iteration 512 invokes undefined behavior
[-Waggressive-loop-optimizations]
w[i]=yy;
~~~~^~~
aggressiveLoop.cc:30:18: note: within this loop
for (int i=0; i<1024; ++i) {
~^~~~~
while in foo2 there is also "auto yy = w[i];"
and in foo3 both assignments
auto zz=z[i];
auto yy = w[i];
will "invokes undefined behavior" at iterations 128 and 512...
