The lim pass (aka loop invariant motion) can move conditional expressions with possible undefined behavior out of the if statement inside a loop which may cause the loop optimization to silently generate wrong code as PR tree-optimization/58143 and PR tree-optimization/58227 demonstrate.
This patch prevents lim from moving code that might cause undefined behavior. This triggered a minor regression in gcc.target/i386/pr53397-1.c: Here lim used to move the expression "2*step" out of the loop, but this may cause undefined behavior on case of overflow, I propose to resolve this by adding -fno-strict-overflow. The test case looks pretty constructed anyway. The patch was boot-strapped and regression tested on i686-pc-linux-gnu and X86_64-linux-gnu OK for trunk? Regards Bernd Edlinger
2013-08-28 Bernd Edlinger <bernd.edlin...@hotmail.de>
PR tree-optimization/58143
PR tree-optimization/58227
Prevent lim from moving conditional expressions
if that could trigger undefined behavior.
* gimple.h (gimple_could_trap_p_2): New function.
* gimple.c (gimple_could_trap_p_2): New function.
(gimple_could_trap_p_1): Call gimple_could_trap_p_2.
* tree-ssa-loop-im.c (movement_possibility): Likewise.
testsuite/
* gcc.dg/pr58143.c: New test.
* gcc.target/i386/pr53397-1.c: Added -fno-strict-overflow.
* gcc.target/i386/pr53397-2.c: Likewise.
patch-lim.diff
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