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commit: 9b342fdeb8588681bb106e072cefd481a045fb21 |
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Author: Sergei Trofimovich <slyfox <AT> gentoo <DOT> org> |
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AuthorDate: Tue Dec 1 19:16:33 2020 +0000 |
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Commit: Sergei Trofimovich <slyfox <AT> gentoo <DOT> org> |
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CommitDate: Tue Dec 1 19:16:33 2020 +0000 |
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URL: https://gitweb.gentoo.org/proj/gcc-patches.git/commit/?id=9b342fde |
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|
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10.2.0: backport strncmp() folding |
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|
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Reported-by: Matt Whitlock |
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Bug: https://bugs.gentoo.org/757792 |
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Bug: https://gcc.gnu.org/PR96758 |
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Signed-off-by: Sergei Trofimovich <slyfox <AT> gentoo.org> |
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|
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10.2.0/gentoo/41_all_strlen-PR96758.patch | 95 +++++++++++++++++++++++++++++++ |
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10.2.0/gentoo/README.history | 3 + |
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2 files changed, 98 insertions(+) |
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|
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diff --git a/10.2.0/gentoo/41_all_strlen-PR96758.patch b/10.2.0/gentoo/41_all_strlen-PR96758.patch |
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new file mode 100644 |
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index 0000000..fccf2de |
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--- /dev/null |
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+++ b/10.2.0/gentoo/41_all_strlen-PR96758.patch |
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@@ -0,0 +1,95 @@ |
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+https://bugs.gentoo.org/757792 |
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+ |
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+From 0dbfa88edafbe913a7a9099246041e0190aa3948 Mon Sep 17 00:00:00 2001 |
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+From: Jakub Jelinek <jakub@××××××.com> |
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+Date: Tue, 25 Aug 2020 13:47:10 +0200 |
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+Subject: [PATCH] strlen: Fix handle_builtin_string_cmp [PR96758] |
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+ |
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+The following testcase is miscompiled, because handle_builtin_string_cmp |
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+sees a strncmp call with constant last argument 4, where one of the strings |
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+has an upper bound of 5 bytes (due to it being an array of that size) and |
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+the other has a known string length of 1 and the result is used only in |
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+equality comparison. |
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+It is folded into __builtin_strncmp_eq (str1, str2, 4), which is |
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+incorrect, because that means reading 4 bytes from both strings and |
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+comparing that. When one of the strings has known strlen of 1, we want to |
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+compare just 2 bytes, not 4, as strncmp shouldn't compare any bytes beyond |
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+the null. |
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+So, the last argument to __builtin_strncmp_eq should be the minimum of the |
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+provided strncmp last argument and the known string length + 1 (assuming |
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+the other string has only a known upper bound due to array size). |
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+ |
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+Besides that, I've noticed the code has been written with the intent to also |
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+support the case where we know exact string length of both strings (but not |
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+the string content, so we can't compute it at compile time). In that case, |
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+both cstlen1 and cstlen2 are non-negative and both arysiz1 and arysiz2 are |
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+negative. We wouldn't optimize that, cmpsiz would be either the strncmp |
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+last argument, or for strcmp the first string length, but varsiz would be |
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+-1 and thus cmpsiz would be never < varsiz. The patch fixes it by using the |
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+correct length, in that case using the minimum of the two and for strncmp |
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+also the last argument. |
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+ |
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+2020-08-25 Jakub Jelinek <jakub@××××××.com> |
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+ |
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+ PR tree-optimization/96758 |
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+ * tree-ssa-strlen.c (handle_builtin_string_cmp): If both cstlen1 |
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+ and cstlen2 are set, set cmpsiz to their minimum, otherwise use the |
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+ one that is set. If bound is used and smaller than cmpsiz, set cmpsiz |
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+ to bound. If both cstlen1 and cstlen2 are set, perform the optimization. |
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+ |
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+ * gcc.dg/strcmpopt_12.c: New test. |
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+ |
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+(cherry picked from commit f982a6ec9b6d98f5f37114b1d7455c54ce5056b8) |
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+--- |
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+ gcc/testsuite/gcc.dg/strcmpopt_12.c | 17 +++++++++++++++++ |
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+ gcc/tree-ssa-strlen.c | 10 +++++++++- |
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+ 2 files changed, 26 insertions(+), 1 deletion(-) |
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+ create mode 100644 gcc/testsuite/gcc.dg/strcmpopt_12.c |
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+ |
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+diff --git a/gcc/testsuite/gcc.dg/strcmpopt_12.c b/gcc/testsuite/gcc.dg/strcmpopt_12.c |
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+new file mode 100644 |
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+index 00000000000..d8077b62f7f |
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+--- /dev/null |
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++++ b/gcc/testsuite/gcc.dg/strcmpopt_12.c |
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+@@ -0,0 +1,17 @@ |
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++/* PR tree-optimization/96758 */ |
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++/* { dg-do run } */ |
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++/* { dg-options "-O2" } */ |
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++ |
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++int v = 1; |
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++ |
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++int |
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++main () |
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++{ |
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++ const char *s = v ? "a" : "b"; |
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++ char x[5]; |
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++ char y[5] = "a\0a"; |
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++ __builtin_memcpy (x, y, sizeof (y)); |
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++ if (__builtin_strncmp (x, s, 4) != 0) |
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++ __builtin_abort (); |
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++ return 0; |
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++} |
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+diff --git a/gcc/tree-ssa-strlen.c b/gcc/tree-ssa-strlen.c |
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+index 93d095e1896..b0874da5d1e 100644 |
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+--- a/gcc/tree-ssa-strlen.c |
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++++ b/gcc/tree-ssa-strlen.c |
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+@@ -4485,7 +4485,15 @@ handle_builtin_string_cmp (gimple_stmt_iterator *gsi, const vr_values *rvals) |
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+ ++cstlen2; |
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+ |
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+ /* The exact number of characters to compare. */ |
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+- HOST_WIDE_INT cmpsiz = bound < 0 ? cstlen1 < 0 ? cstlen2 : cstlen1 : bound; |
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++ HOST_WIDE_INT cmpsiz; |
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++ if (cstlen1 >= 0 && cstlen2 >= 0) |
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++ cmpsiz = MIN (cstlen1, cstlen2); |
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++ else if (cstlen1 >= 0) |
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++ cmpsiz = cstlen1; |
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++ else |
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++ cmpsiz = cstlen2; |
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++ if (bound >= 0) |
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++ cmpsiz = MIN (cmpsiz, bound); |
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+ /* The size of the array in which the unknown string is stored. */ |
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+ HOST_WIDE_INT varsiz = arysiz1 < 0 ? arysiz2 : arysiz1; |
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+ |
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+-- |
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+2.29.2 |
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+ |
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|
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diff --git a/10.2.0/gentoo/README.history b/10.2.0/gentoo/README.history |
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index e0207e7..8b8c475 100644 |
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--- a/10.2.0/gentoo/README.history |
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+++ b/10.2.0/gentoo/README.history |
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@@ -1,3 +1,6 @@ |
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+5 TODO |
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+ + 41_all_strlen-PR96758.patch |
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+ |
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4 04 Nov 2020 |
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+ 40_all_ipa-to_frequency.patch |
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