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From: "sam at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug ada/37604] New: Suboptimal code generation for volatile access Date: Sat, 20 Sep 2008 20:15:00 -0000 [thread overview] Message-ID: <bug-37604-15321@http.gcc.gnu.org/bugzilla/> (raw) The following code generates suboptimal code on i686-pc-linux-gnu: with Interfaces; use Interfaces; with System.Storage_Elements; package A is Var : unsigned_8; for Var'Address use System.Storage_Elements.To_Address (1000); pragma Volatile (Var); end A; with A; with Interfaces; use Interfaces; procedure U is begin A.Var := A.Var or 1; A.Var := A.Var or 2; end U; With -O3 -fomit-frame-pointer, we get: _ada_u: movl a__var, %edx <=== indirection instead of... movzbl (%edx), %eax <=== ...direct access here orl $1, %eax movb %al, (%edx) movl a__var, %edx <=== useless reloading of a__var movzbl (%edx), %eax orl $2, %eax movb %al, (%edx) ret If the variable is declared in the same compilation unit, we get: _ada_u: movzbl 1000, %eax orl $1, %eax movb %al, 1000 movzbl 1000, %eax orl $2, %eax movb %al, 1000 ret We should probably get the same code in both cases. -- Summary: Suboptimal code generation for volatile access Product: gcc Version: 4.4.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: ada AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: sam at gcc dot gnu dot org GCC host triplet: i686-pc-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37604
next reply other threads:[~2008-09-20 20:15 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-09-20 20:15 sam at gcc dot gnu dot org [this message] 2008-09-21 12:21 ` [Bug ada/37604] " rguenth at gcc dot gnu dot org 2008-09-21 12:25 ` sam at gcc dot gnu dot org
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