Successfully identified regression in *gcc* in CI configuration tcwg_gcc_bootstrap/master-arm-bootstrap_debug. So far, this commit has regressed CI configurations: - tcwg_gcc_bootstrap/master-arm-bootstrap_debug
Culprit: <cut> commit 1d244020246cb155e4de62ca3b302b920a1f513f Author: Roger Sayle roger@nextmovesoftware.com Date: Mon Aug 23 12:37:04 2021 +0100
Fold sign of LSHIFT_EXPR to eliminate no-op conversions.
This short patch teaches fold that it is "safe" to change the sign of a left shift, to reduce the number of type conversions in gimple. As an example:
unsigned int foo(unsigned int i) { return (int)i << 8; }
is currently optimized to:
unsigned int foo (unsigned int i) { int i.0_1; int _2; unsigned int _4;
<bb 2> [local count: 1073741824]: i.0_1 = (int) i_3(D); _2 = i.0_1 << 8; _4 = (unsigned int) _2; return _4; }
with this patch, this now becomes:
unsigned int foo (unsigned int i) { unsigned int _2;
<bb 2> [local count: 1073741824]: _2 = i_1(D) << 8; return _2; }
which generates exactly the same assembly language. Aside from the reduced memory usage, the real benefit is that no-op conversions tend to interfere with many folding optimizations. For example,
unsigned int bar(unsigned char i) { return (i ^ (i<<16)) | (i<<8); }
currently gets (tangled in conversions and) optimized to:
unsigned int bar (unsigned char i) { unsigned int _1; unsigned int _2; int _3; int _4; unsigned int _6; unsigned int _8;
<bb 2> [local count: 1073741824]: _1 = (unsigned int) i_5(D); _2 = _1 * 65537; _3 = (int) i_5(D); _4 = _3 << 8; _8 = (unsigned int) _4; _6 = _2 | _8; return _6; }
but with this patch, bar now optimizes down to:
unsigned int bar(unsigned char i) { unsigned int _1; unsigned int _4;
<bb 2> [local count: 1073741824]: _1 = (unsigned int) i_3(D); _4 = _1 * 65793; return _4;
}
2021-08-23 Roger Sayle roger@nextmovesoftware.com
gcc/ChangeLog * match.pd (shift transformations): Change the sign of an LSHIFT_EXPR if it reduces the number of explicit conversions.
gcc/testsuite/ChangeLog * gcc.dg/fold-convlshift-1.c: New test case. * gcc.dg/fold-convlshift-2.c: New test case. </cut>
Results regressed to (for first_bad == 1d244020246cb155e4de62ca3b302b920a1f513f) # reset_artifacts: -10 # true: 0 # build_abe binutils: 1 # First few build errors in logs: # 00:06:26 make[3]: [armv8l-unknown-linux-gnueabihf/bits/largefile-config.h] Error 1 (ignored) # 00:25:39 make[3]: [armv8l-unknown-linux-gnueabihf/bits/largefile-config.h] Error 1 (ignored) # 00:29:38 /home/tcwg-buildslave/workspace/tcwg_gnu_8/abe/snapshots/gcc.git~master/gcc/bitmap.h:357:13: error: type mismatch in ‘lshift_expr’ # 00:29:38 /home/tcwg-buildslave/workspace/tcwg_gnu_8/abe/snapshots/gcc.git~master/gcc/bitmap.h:357:13: internal compiler error: ‘verify_gimple’ failed # 00:29:38 make[3]: *** [bitmap.o] Error 1 # 00:34:06 make[2]: *** [all-stage3-gcc] Error 2 # 00:34:06 make[1]: *** [stage3-bubble] Error 2 # 00:34:07 make: *** [all] Error 2
from (for last_good == b320edc0c29c838b0090c3c9be14187d132f73f2) # reset_artifacts: -10 # true: 0 # build_abe binutils: 1 # build_abe bootstrap_debug: 2
Artifacts of last_good build: https://ci.linaro.org/job/tcwg_gcc_bootstrap-bisect-master-arm-bootstrap_deb... Artifacts of first_bad build: https://ci.linaro.org/job/tcwg_gcc_bootstrap-bisect-master-arm-bootstrap_deb... Build top page/logs: https://ci.linaro.org/job/tcwg_gcc_bootstrap-bisect-master-arm-bootstrap_deb...
Configuration details:
Reproduce builds: <cut> mkdir investigate-gcc-1d244020246cb155e4de62ca3b302b920a1f513f cd investigate-gcc-1d244020246cb155e4de62ca3b302b920a1f513f
git clone https://git.linaro.org/toolchain/jenkins-scripts
mkdir -p artifacts/manifests curl -o artifacts/manifests/build-baseline.sh https://ci.linaro.org/job/tcwg_gcc_bootstrap-bisect-master-arm-bootstrap_deb... --fail curl -o artifacts/manifests/build-parameters.sh https://ci.linaro.org/job/tcwg_gcc_bootstrap-bisect-master-arm-bootstrap_deb... --fail curl -o artifacts/test.sh https://ci.linaro.org/job/tcwg_gcc_bootstrap-bisect-master-arm-bootstrap_deb... --fail chmod +x artifacts/test.sh
# Reproduce the baseline build (build all pre-requisites) ./jenkins-scripts/tcwg_gnu-build.sh @@ artifacts/manifests/build-baseline.sh
# Save baseline build state (which is then restored in artifacts/test.sh) mkdir -p ./bisect rsync -a --del --delete-excluded --exclude /bisect/ --exclude /artifacts/ --exclude /gcc/ ./ ./bisect/baseline/
cd gcc
# Reproduce first_bad build git checkout --detach 1d244020246cb155e4de62ca3b302b920a1f513f ../artifacts/test.sh
# Reproduce last_good build git checkout --detach b320edc0c29c838b0090c3c9be14187d132f73f2 ../artifacts/test.sh
cd .. </cut>
History of pending regressions and results: https://git.linaro.org/toolchain/ci/base-artifacts.git/log/?h=linaro-local/c...
Artifacts: https://ci.linaro.org/job/tcwg_gcc_bootstrap-bisect-master-arm-bootstrap_deb... Build log: https://ci.linaro.org/job/tcwg_gcc_bootstrap-bisect-master-arm-bootstrap_deb...
Full commit (up to 1000 lines): <cut> commit 1d244020246cb155e4de62ca3b302b920a1f513f Author: Roger Sayle roger@nextmovesoftware.com Date: Mon Aug 23 12:37:04 2021 +0100
Fold sign of LSHIFT_EXPR to eliminate no-op conversions.
This short patch teaches fold that it is "safe" to change the sign of a left shift, to reduce the number of type conversions in gimple. As an example:
unsigned int foo(unsigned int i) { return (int)i << 8; }
is currently optimized to:
unsigned int foo (unsigned int i) { int i.0_1; int _2; unsigned int _4;
<bb 2> [local count: 1073741824]: i.0_1 = (int) i_3(D); _2 = i.0_1 << 8; _4 = (unsigned int) _2; return _4; }
with this patch, this now becomes:
unsigned int foo (unsigned int i) { unsigned int _2;
<bb 2> [local count: 1073741824]: _2 = i_1(D) << 8; return _2; }
which generates exactly the same assembly language. Aside from the reduced memory usage, the real benefit is that no-op conversions tend to interfere with many folding optimizations. For example,
unsigned int bar(unsigned char i) { return (i ^ (i<<16)) | (i<<8); }
currently gets (tangled in conversions and) optimized to:
unsigned int bar (unsigned char i) { unsigned int _1; unsigned int _2; int _3; int _4; unsigned int _6; unsigned int _8;
<bb 2> [local count: 1073741824]: _1 = (unsigned int) i_5(D); _2 = _1 * 65537; _3 = (int) i_5(D); _4 = _3 << 8; _8 = (unsigned int) _4; _6 = _2 | _8; return _6; }
but with this patch, bar now optimizes down to:
unsigned int bar(unsigned char i) { unsigned int _1; unsigned int _4;
<bb 2> [local count: 1073741824]: _1 = (unsigned int) i_3(D); _4 = _1 * 65793; return _4;
}
2021-08-23 Roger Sayle roger@nextmovesoftware.com
gcc/ChangeLog * match.pd (shift transformations): Change the sign of an LSHIFT_EXPR if it reduces the number of explicit conversions.
gcc/testsuite/ChangeLog * gcc.dg/fold-convlshift-1.c: New test case. * gcc.dg/fold-convlshift-2.c: New test case. --- gcc/match.pd | 9 +++++++++ gcc/testsuite/gcc.dg/fold-convlshift-1.c | 20 ++++++++++++++++++++ gcc/testsuite/gcc.dg/fold-convlshift-2.c | 20 ++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/gcc/match.pd b/gcc/match.pd index 0fcfd0ea62c..978a1b0172e 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -3385,6 +3385,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) (if (integer_zerop (@2) || integer_all_onesp (@2)) (cmp @0 @2)))))
+/* Both signed and unsigned lshift produce the same result, so use + the form that minimizes the number of conversions. */ +(simplify + (convert (lshift:s@0 (convert:s@1 @2) INTEGER_CST@3)) + (if (tree_nop_conversion_p (type, TREE_TYPE (@0)) + && INTEGRAL_TYPE_P (TREE_TYPE (@2)) + && TYPE_PRECISION (TREE_TYPE (@2)) <= TYPE_PRECISION (type)) + (lshift (convert @2) @3))) + /* Simplifications of conversions. */
/* Basic strip-useless-type-conversions / strip_nops. */ diff --git a/gcc/testsuite/gcc.dg/fold-convlshift-1.c b/gcc/testsuite/gcc.dg/fold-convlshift-1.c new file mode 100644 index 00000000000..b6f57f81e72 --- /dev/null +++ b/gcc/testsuite/gcc.dg/fold-convlshift-1.c @@ -0,0 +1,20 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +unsigned int foo(unsigned int i) +{ + int t1 = i; + int t2 = t1 << 8; + return t2; +} + +int bar(int i) +{ + unsigned int t1 = i; + unsigned int t2 = t1 << 8; + return t2; +} + +/* { dg-final { scan-tree-dump-not "\(int\)" "optimized" } } */ +/* { dg-final { scan-tree-dump-not "\(unsigned int\)" "optimized" } } */ + diff --git a/gcc/testsuite/gcc.dg/fold-convlshift-2.c b/gcc/testsuite/gcc.dg/fold-convlshift-2.c new file mode 100644 index 00000000000..f21358c4584 --- /dev/null +++ b/gcc/testsuite/gcc.dg/fold-convlshift-2.c @@ -0,0 +1,20 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +unsigned int foo(unsigned char c) +{ + int t1 = c; + int t2 = t1 << 8; + return t2; +} + +int bar(unsigned char c) +{ + unsigned int t1 = c; + unsigned int t2 = t1 << 8; + return t2; +} + +/* { dg-final { scan-tree-dump-times "\(int\)" 1 "optimized" } } */ +/* { dg-final { scan-tree-dump-times "\(unsigned int\)" 1 "optimized" } } */ + </cut>