fwprop.c currently has a bug where a successful propagation to one operand of an instruction will prevent propagation to any remaining operands.
The cause is due to the use of loc_mentioned_in_p() to check that a reference, provided by earlier DF scan, still exist in an instruction. The test is intended to check that an earlier propagation and simplification has not removed D/U references. However, loc_mentioned_in_p(), compares addresses of rtx to determine equivalence. If an instruction has already been modified and simplified, this will longer apply - even if the def/use is still valid. This problem was already noted in Nov, but no bug report seems to have been filed. http://gcc.gnu.org/ml/gcc-patches/2007-11/msg00170.html I will attach patch, that uses reg_mentioned_p() as a substitute. The only differences I noted where: a) reg_mentioned_p() does not match physical sub registers of longer hard registers. This seems to have no consequence since fwprop entirely rejects hard_registers in latter code. Perhaps for clarity, hard registers could be ignored earlier. b) registers in asm_operands are found. Which seems beneficial if they are pseudos and again ignored if they are hard registers. I am only able to test this with AVR port. In that it was 100% successful with no regressions of torture/execute testsuite. -- Summary: fwprop only propagates one operand Product: gcc Version: 4.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: rtl-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: hutchinsonandy at aim dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35542
