LLVM vs NCG: floating point numbers close to zero have different sign

Compiling HEAD with perf-llvm, (3.4.2) and running the nofib suite fails at the wave4main case. It is not clear to me whether wave4main should always produce the same output (and so the test fails because it does not do so) or whether the numbers generated depend on some feature of the build settings, or OS.

HC = /Users/xxx/Projects/ghc/inplace/bin/ghc-stage2
HC_OPTS = -O2 -Rghc-timing -H32m -hisuf hi -cpp -fglasgow-exts -rtsopts
RUNTEST_OPTS = -ghc-timing
==nofib== wave4main: size of wave4main follows...
__TEXT	__DATA	__OBJC	others	dec	hex
4091904	450560	0	4295947176	4300489640	1005443a8
==nofib== wave4main: time to run wave4main follows...
../../../runstdtest/runstdtest ./wave4main  -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3 -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3  -ghc-timing     4000;   ../../../runstdtest/runstdtest ./wave4main  -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3 -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3  -ghc-timing     4000;   ../../../runstdtest/runstdtest ./wave4main  -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3 -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3  -ghc-timing     4000;   ../../../runstdtest/runstdtest ./wave4main  -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3 -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3  -ghc-timing     4000;   ../../../runstdtest/runstdtest ./wave4main  -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3 -o1 wave4main.stdout -o1 wave4main.stdout2 -o1 wave4main.stdout3  -ghc-timing     4000;

real	0m0.217s
user	0m0.191s
sys	0m0.011s
././wave4main 4000 < /dev/null
expected stdout not matched by reality
--- wave4main.stdout	2014-07-08 20:57:14.000000000 +0100
+++ /var/folders/d9/94xh7l810mz3_skcsfh68khh0000gn/T//runtest16932.1	2014-07-13 13:43:22.000000000 +0100
@@ -1 +1 @@
-69923/1465
+69096/1465

real	0m0.197s
user	0m0.186s
sys	0m0.008s
././wave4main 4000 < /dev/null
expected stdout not matched by reality
--- wave4main.stdout	2014-07-08 20:57:14.000000000 +0100
+++ /var/folders/d9/94xh7l810mz3_skcsfh68khh0000gn/T//runtest16961.1	2014-07-13 13:43:22.000000000 +0100
@@ -1 +1 @@
-69923/1465
+69096/1465

real	0m0.201s
user	0m0.189s
sys	0m0.009s
././wave4main 4000 < /dev/null
expected stdout not matched by reality
--- wave4main.stdout	2014-07-08 20:57:14.000000000 +0100
+++ /var/folders/d9/94xh7l810mz3_skcsfh68khh0000gn/T//runtest17011.1	2014-07-13 13:43:22.000000000 +0100
@@ -1 +1 @@
-69923/1465
+69096/1465

real	0m0.201s
user	0m0.190s
sys	0m0.008s
././wave4main 4000 < /dev/null
expected stdout not matched by reality
--- wave4main.stdout	2014-07-08 20:57:14.000000000 +0100
+++ /var/folders/d9/94xh7l810mz3_skcsfh68khh0000gn/T//runtest17051.1	2014-07-13 13:43:23.000000000 +0100
@@ -1 +1 @@
-69923/1465
+69096/1465

real	0m0.200s
user	0m0.189s
sys	0m0.009s
././wave4main 4000 < /dev/null
expected stdout not matched by reality
--- wave4main.stdout	2014-07-08 20:57:14.000000000 +0100
+++ /var/folders/d9/94xh7l810mz3_skcsfh68khh0000gn/T//runtest17080.1	2014-07-13 13:43:23.000000000 +0100
@@ -1 +1 @@
-69923/1465
+69096/1465
make: *** [runtests] Error 1

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	NoFib benchmark suite
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed milestone to %7.10.1

changed weight to 5

added Tbug Trac import nofib labels

changed weight to 3

I'm pretty sure I know why this is happening. Basically this program's output is very sensitive to whether certain floating-point numbers that are very close to zero wind up being positive or negative. It might be worth tracking down exactly why the behavior differs when GHC is built with LLVM at some point though.

Trac metadata

Trac field	Value
Priority	normal → low

changed title from wave4main in nofib fails to LLVM vs NCG: floating point numbers close to zero have different sign

Trac metadata

Trac field	Value
Component	NoFib benchmark suite → Compiler (NCG)

added NCG backend label and removed nofib label

removed milestone

Moving to 7.12.1 milestone; if you feel this is an error and should be addressed sooner, please move it back to the 7.10.1 milestone.

changed milestone to %8.0.1

Milestone renamed

Is this reproducible on 8.4.1 with llvm 5.0?

added incorrect runtime result nofib labels

added Plow label