PR85678: Change default to -fno-common
GCC currently defaults to -fcommon. As discussed in the PR, this is an ancient
C feature which is not conforming with the latest C standards. On many targets
this means global variable accesses have a codesize and performance penalty.
This applies to C code only, C++ code is not affected by -fcommon. It is about
time to change the default.
gcc/
PR85678
* common.opt (fcommon): Change init to 1.
* invoke.texi (-fcommon): Update documentation.
testsuite/
* g++.dg/lto/odr-6_1.c: Add -fcommon.
* gcc.dg/alias-15.c: Likewise.
* gcc.dg/fdata-sections-1.c: Likewise.
* gcc.dg/ipa/pr77653.c: Likewise.
* gcc.dg/lto/20090729_0.c: Likewise.
* gcc.dg/lto/20111207-1_0.c: Likewise.
* gcc.dg/lto/c-compatible-types-1_0.c: Likewise.
* gcc.dg/lto/pr55525_0.c: Likewise.
* gcc.dg/lto/pr88077_0.c: Use long to avoid alignment warning.
* gcc.dg/lto/pr88077_1.c: Add -fcommon.
* gcc.target/aarch64/sve/peel_ind_1.c: Allow ANCHOR0.
* gcc.target/aarch64/sve/peel_ind_2.c: Likewise.
* gcc.target/aarch64/sve/peel_ind_3.c: Likewise.
* gcc.target/i386/volatile-bitfields-2.c: Allow movl or movq.
From-SVN: r278509
This commit is contained in:
Wilco Dijkstra
Wilco Dijkstra
parent
83115e9eb8
commit
6271dd984d
18 changed files with 57 additions and 38 deletions
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@ -1,3 +1,9 @@
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2019-11-20 Wilco Dijkstra <wdijkstr@arm.com>
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PR85678
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* common.opt (fcommon): Change init to 1.
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* doc/invoke.texi (-fcommon): Update documentation.
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2019-11-20 Jan Hubicka <jh@suse.cz>
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* fibonacci_heap.h (fibonacci_heap<K,V>::consolidate): Turn auto_vec
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@ -1131,7 +1131,7 @@ Common Report Var(flag_combine_stack_adjustments) Optimization
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Looks for opportunities to reduce stack adjustments and stack references.
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fcommon
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Common Report Var(flag_no_common,0)
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Common Report Var(flag_no_common,0) Init(1)
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Put uninitialized globals in the common section.
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fcompare-debug
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@ -569,7 +569,7 @@ Objective-C and Objective-C++ Dialects}.
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-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
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-fasynchronous-unwind-tables @gol
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-fno-gnu-unique @gol
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-finhibit-size-directive -fno-common -fno-ident @gol
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-finhibit-size-directive -fcommon -fno-ident @gol
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-fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol
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-fno-jump-tables @gol
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-frecord-gcc-switches @gol
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@ -14112,35 +14112,27 @@ useful for building programs to run under WINE@.
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code that is not binary compatible with code generated without that switch.
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Use it to conform to a non-default application binary interface.
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@item -fno-common
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@opindex fno-common
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@item -fcommon
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@opindex fcommon
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@opindex fno-common
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@cindex tentative definitions
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In C code, this option controls the placement of global variables
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defined without an initializer, known as @dfn{tentative definitions}
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in the C standard. Tentative definitions are distinct from declarations
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In C code, this option controls the placement of global variables
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defined without an initializer, known as @dfn{tentative definitions}
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in the C standard. Tentative definitions are distinct from declarations
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of a variable with the @code{extern} keyword, which do not allocate storage.
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Unix C compilers have traditionally allocated storage for
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uninitialized global variables in a common block. This allows the
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linker to resolve all tentative definitions of the same variable
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in different compilation units to the same object, or to a non-tentative
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definition.
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This is the behavior specified by @option{-fcommon}, and is the default for
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GCC on most targets.
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On the other hand, this behavior is not required by ISO
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C, and on some targets may carry a speed or code size penalty on
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variable references.
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The default is @option{-fno-common}, which specifies that the compiler places
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uninitialized global variables in the BSS section of the object file.
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This inhibits the merging of tentative definitions by the linker so you get a
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multiple-definition error if the same variable is accidentally defined in more
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than one compilation unit.
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The @option{-fno-common} option specifies that the compiler should instead
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place uninitialized global variables in the BSS section of the object file.
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This inhibits the merging of tentative definitions by the linker so
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you get a multiple-definition error if the same
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variable is defined in more than one compilation unit.
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Compiling with @option{-fno-common} is useful on targets for which
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it provides better performance, or if you wish to verify that the
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program will work on other systems that always treat uninitialized
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variable definitions this way.
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The @option{-fcommon} places uninitialized global variables in a common block.
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This allows the linker to resolve all tentative definitions of the same variable
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in different compilation units to the same object, or to a non-tentative
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definition. This behavior does not conform to ISO C, is inconsistent with C++,
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and on many targets implies a speed and code size penalty on global variable
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references. It is mainly useful to enable legacy code to link without errors.
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@item -fno-ident
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@opindex fno-ident
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@ -1,3 +1,21 @@
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2019-11-20 Wilco Dijkstra <wdijkstr@arm.com>
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PR85678
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* g++.dg/lto/odr-6_1.c: Add -fcommon.
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* gcc.dg/alias-15.c: Likewise.
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* gcc.dg/fdata-sections-1.c: Likewise.
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* gcc.dg/ipa/pr77653.c: Likewise.
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* gcc.dg/lto/20090729_0.c: Likewise.
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* gcc.dg/lto/20111207-1_0.c: Likewise.
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* gcc.dg/lto/c-compatible-types-1_0.c: Likewise.
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* gcc.dg/lto/pr55525_0.c: Likewise.
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* gcc.dg/lto/pr88077_0.c: Use long to avoid alignment warning.
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* gcc.dg/lto/pr88077_1.c: Add -fcommon.
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* gcc.target/aarch64/sve/peel_ind_1.c: Allow ANCHOR0.
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* gcc.target/aarch64/sve/peel_ind_2.c: Likewise.
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* gcc.target/aarch64/sve/peel_ind_3.c: Likewise.
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* gcc.target/i386/volatile-bitfields-2.c: Allow movl or movq.
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2019-11-20 Richard Biener <rguenther@suse.de>
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* gcc.dg/vect/bb-slp-42.c: Adjust.
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@ -1,3 +1,4 @@
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/* { dg-options {-fcommon} } */
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struct {} admbaserest_; // { dg-lto-message "type of " 2 }
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@ -1,5 +1,5 @@
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/* { dg-do compile } */
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/* { dg-additional-options "-O2 -fdump-ipa-cgraph" } */
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/* { dg-additional-options "-O2 -fcommon -fdump-ipa-cgraph" } */
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/* RTL-level CSE shouldn't introduce LCO (for the string) into varpool */
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char *p;
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@ -2,7 +2,7 @@
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/* Origin: Jonathan Larmour <jifl-bugzilla@jifvik.org> */
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/* { dg-do compile { target *-*-linux* *-*-gnu* *-*-uclinux* } } */
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/* { dg-options "-fdata-sections" } */
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/* { dg-options "-fcommon -fdata-sections" } */
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int x;
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@ -1,5 +1,5 @@
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/* { dg-require-alias "" } */
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/* { dg-options "-O2 -fdump-ipa-icf-details" } */
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/* { dg-options "-O2 -fcommon -fdump-ipa-icf-details" } */
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int a, b, c, d, e, h, i, j, k, l;
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const int f;
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@ -1,4 +1,4 @@
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/* { dg-lto-options "-w" } */
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/* { dg-lto-options { {-fcommon -w} {-fcommon} } } */
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double i;
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int j;
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@ -1,4 +1,4 @@
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/* { dg-lto-do run } */
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/* { dg-lto-options { { -flto } } } */
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/* { dg-lto-options { { -flto -fcommon } {-fcommon} {-fcommon} {-fcommon} } } */
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/* { dg-require-linker-plugin "" } */
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/* { dg-extra-ld-options "-fuse-linker-plugin" } */
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@ -1,5 +1,5 @@
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/* { dg-lto-do run } */
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/* { dg-lto-options "-O3" } */
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/* { dg-lto-options { {-O3 -fcommon} {-fcommon} } } */
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/* By C standard Each enumerated type shall be compatible with char, a signed
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integer, type, or an unsigned integer type. The choice of type is
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@ -1,5 +1,5 @@
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/* { dg-lto-do link } */
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/* { dg-lto-options { { -flto -w } } } */
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/* { dg-lto-options { { -fcommon -flto -w } } } */
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char s[sizeof (char *)];
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int main(void)
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@ -1,3 +1,3 @@
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/* { dg-lto-do link } */
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int HeaderStr;
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long HeaderStr;
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@ -1,3 +1,5 @@
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/* { dg-options {-fcommon} } */
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char HeaderStr[1];
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int main()
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@ -21,7 +21,7 @@ foo (void)
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}
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/* We should operate on aligned vectors. */
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/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, x\n} } } */
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/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, (x|\.LANCHOR0)\n} } } */
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/* We should use an induction that starts at -5, with only the last
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7 elements of the first iteration being active. */
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/* { dg-final { scan-assembler {\tindex\tz[0-9]+\.s, #-5, #5\n} } } */
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@ -17,7 +17,7 @@ foo (void)
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}
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/* We should operate on aligned vectors. */
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/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, x\n} } } */
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/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, (x|\.LANCHOR0)\n} } } */
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/* We should unroll the loop three times. */
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/* { dg-final { scan-assembler-times "\tst1w\t" 3 } } */
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/* { dg-final { scan-assembler {\tptrue\t(p[0-9]+)\.s, vl7\n.*\teor\tp[0-7]\.b, (p[0-7])/z, (\1\.b, \2\.b|\2\.b, \1\.b)\n} } } */
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@ -17,5 +17,5 @@ foo (int start)
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}
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/* We should operate on aligned vectors. */
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/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, x\n} } } */
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/* { dg-final { scan-assembler {\t(adrp|adr)\tx[0-9]+, (x|\.LANCHOR0)\n} } } */
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/* { dg-final { scan-assembler {\tubfx\t} } } */
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@ -14,4 +14,4 @@ int foo ()
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return bits.b;
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}
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/* { dg-final { scan-assembler "movl.*bits" } } */
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/* { dg-final { scan-assembler "mov(q|l).*bits" } } */
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