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POGCC compiler options: which set of enabled options is correct?
 

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  1. POGCC compiler options: which set of enabled options is correct?
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    <p>I am trying to figure out which compiler options are enabled for GCC (4.7.3, Macports installation on Mac OS X 10.6.8). I know of the following methods:</p> <ol> <li><p>Using the -Q option with a simple input file as suggested by <a href="https://stackoverflow.com/questions/3138335/gcc-4-3-3-compiler-options-enabled-by-default">GCC 4.3.3 compiler options enabled</a>:</p> <pre><code>gcc -Q -v -o hello hello.c </code></pre></li> <li><p>Using the -Q --help=x combination (for values of x, see <a href="http://gcc.gnu.org/onlinedocs/gcc-4.7.3/gcc/Overall-Options.html#index-help-87" rel="nofollow noreferrer">GCC documentation</a>) e.g:</p> <pre><code>gcc -Q --help=target </code></pre></li> <li><p>To see enabled defines:</p> <pre><code>echo "" | gcc -E -dM - | sort </code></pre></li> </ol> <p>However, when I run method 1 and 2 with the same set of optimization options I get two different sets of enabled/disabled options.</p> <pre><code>$ gcc -Q -v -O3 -march=native -o hello hello.c GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 options passed: -v -D__DYNAMIC__ hello.c -march=corei7-avx -mcx16 -msahf -mno-movbe -maes -mpclmul -mpopcnt -mno-abm -mno-lwp -mno-fma -mno-fma4 -mno-xop -mno-bmi -mno-bmi2 -mno-tbm -mavx -mno-avx2 -msse4.2 -msse4.1 -mno-lzcnt -mno-rdrnd -mno-f16c -mno-fsgsbase --param l1-cache-size=32 --param l1-cache-line-size=64 --param l2-cache-size=6144 -mtune=corei7-avx -fPIC -mmacosx-version-min=10.6.8 -O3 options enabled: -Wnonportable-cfstrings -fPIC -falign-labels -fasynchronous-unwind-tables -fauto-inc-dec -fbranch-count-reg -fcaller-saves -fcombine-stack-adjustments -fcommon -fcompare-elim -fcprop-registers -fcrossjumping -fcse-follow-jumps -fdebug-types-section -fdefer-pop -fdelete-null-pointer-checks -fdevirtualize -fearly-inlining ... </code></pre> <p>whereas</p> <pre><code>$ gcc -Q -O3 -march=native --help=optimizers -falign-functions [enabled] -falign-jumps [enabled] -falign-labels [enabled] -falign-loops [enabled] -fasynchronous-unwind-tables [enabled] -fbranch-count-reg [enabled] -fbranch-probabilities [disabled] -fbranch-target-load-optimize [disabled] -fbranch-target-load-optimize2 [disabled] -fbtr-bb-exclusive [disabled] -fcaller-saves [enabled] -fcombine-stack-adjustments [enabled] -fcommon [enabled] -fcompare-elim [enabled] -fconserve-stack [disabled] -fcprop-registers [enabled] -fcrossjumping [enabled] -fcse-follow-jumps [enabled] -fcx-fortran-rules [disabled] -fcx-limited-range [disabled] -fdata-sections [disabled] -fdce [enabled] -fdefer-pop [enabled] -fdelayed-branch [disabled] -fdelete-null-pointer-checks [enabled] -fdevirtualize [enabled] -fdse [enabled] -fearly-inlining [enabled] ... </code></pre> <p>Looking at options -falign-functions, -falign-jumps, -falign-labels, and -falign-loops Method 2 claims they are all enabled, while Method 1 says only -falign-labels is enabled. Also options -fdce and -fdse are enabled according to Method 2 but not according to Method 1.</p> <p><b>Question</b>: which method should I trust?</p> <p><i>Side note</i>: the list of method 2 is incomplete, because the options are grouped and only the group(s) requested with the --help= option are listed. To see <i>all</i> options in method 2 run:</p> <pre><code>$ gcc -Q -O3 -march=native --help=optimizers --help=target --help=c --help=common --help=warnings | sort </code></pre>
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