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From: "roberto dot costa at st dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/29333] New: Generation of MAX_EXPRs and MIN_EXPRs missed by phiopt Date: Tue, 03 Oct 2006 16:04:00 -0000 [thread overview] Message-ID: <bug-29333-13346@http.gcc.gnu.org/bugzilla/> (raw) There are cases in which phiopt doesn't recognize MAX_EXPRs or MIN_EXPRs patterns. In particular, source codes that look very similar at first sight may induce phiopt to behave differently. Let's consider the following two functions: ----------------------------- int minmax_correct(int a) { if (a > 32767) a = 32767; else if (a < -32768) a = -32768; return a; } int minmax_wrong(int a) { if (a > 32767) a = 32767; if (a < -32768) a = -32768; return a; } ----------------------------- MIN_EXPRs and MAX_EXPRs are generated for the first function, but not for the second. Here is the contents of trace file minmax.c.042t.phicprop1: ----------------------------- ;; Function minmax_correct (minmax_correct) minmax_correct (a) { <bb 2>: if (a_2 > 32767) goto <L3>; else goto <L1>; <L1>:; if (a_2 < -32768) goto <L2>; else goto <L3>; <L2>:; # a_1 = PHI <32767(2), a_2(3), -32768(4)>; <L3>:; <retval> = a_1; return <retval>; } ;; Function minmax_wrong (minmax_wrong) Removing basic block 6 minmax_wrong (a) { <bb 2>: if (a_3 > 32767) goto <L6>; else goto <L1>; <L1>:; if (a_3 < -32768) goto <L3>; else goto <L6>; # a_9 = PHI <a_3(3), 32767(2)>; <L6>:; # a_2 = PHI <a_9(4), -32768(3)>; <L3>:; <retval> = a_2; return <retval>; } ----------------------------- And here is minmax.c.043t.phiopt1: ----------------------------- ;; Function minmax_correct (minmax_correct) Removing basic block 4 Removing basic block 3 Merging blocks 2 and 5 minmax_correct (a) { <bb 2>: a_7 = MAX_EXPR <-32768, a_2>; a_8 = MIN_EXPR <a_7, 32767>; <retval> = a_8; return <retval>; } ;; Function minmax_wrong (minmax_wrong) minmax_wrong (a) { <bb 2>: if (a_3 > 32767) goto <L6>; else goto <L1>; <L1>:; if (a_3 < -32768) goto <L3>; else goto <L6>; # a_9 = PHI <a_3(3), 32767(2)>; <L6>:; # a_2 = PHI <a_9(4), -32768(3)>; <L3>:; <retval> = a_2; return <retval>; } ----------------------------- -- Summary: Generation of MAX_EXPRs and MIN_EXPRs missed by phiopt Product: gcc Version: 4.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: roberto dot costa at st dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29333
next reply other threads:[~2006-10-03 16:04 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2006-10-03 16:04 roberto dot costa at st dot com [this message] 2006-10-03 16:05 ` [Bug tree-optimization/29333] " roberto dot costa at st dot com 2006-10-03 16:06 ` pinskia at gcc dot gnu dot org 2006-10-03 16:11 ` [Bug tree-optimization/29333] Jump threading getting in the way of PHI-OPT pinskia at gcc dot gnu dot org 2006-10-05 8:15 ` roberto dot costa at st dot com
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