Commit Graph

4 Commits

Author SHA1 Message Date
Andrew Trick e4083f9e85 Disabled subregister copy coalescing during MachineCSE.
This effectively backs out r197465 but leaves some of the general
fixes in place. Not all targets are ready to handle this feature. To
enable it, some infrastructure work is needed to better handle
register class constraints.

llvm-svn: 197514
2013-12-17 19:29:36 +00:00
Andrew Trick e339828b90 Allow MachineCSE to coalesce trivial subregister copies the same way that it coalesces normal copies.
Without this, MachineCSE is powerless to handle redundant operations with truncated source operands.

This required fixing the 2-addr pass to handle tied subregisters. It isn't clear what combinations of subregisters can legally be tied, but the simple case of truncated source operands is now safely handled:

     %vreg11<def> = COPY %vreg1:sub_32bit; GR32:%vreg11 GR64:%vreg1
     %vreg12<def> = COPY %vreg2:sub_32bit; GR32:%vreg12 GR64:%vreg2
     %vreg13<def,tied1> = ADD32rr %vreg11<tied0>, %vreg12<kill>, %EFLAGS<imp-def>

Test case: cse-add-with-overflow.ll.

This exposed an existing bug in
PPCInstrInfo::commuteInstruction. Thanks to Rafael for the test case:
PowerPC/crash.ll.

llvm-svn: 197465
2013-12-17 04:50:45 +00:00
Rafael Espindola f152836788 Revert "Allow MachineCSE to coalesce trivial subregister copies the same way that it coalesces normal copies."
This reverts commit r197414.

It broke the ppc64 bootstrap. I will post a testcase in a sec.

llvm-svn: 197424
2013-12-16 20:57:09 +00:00
Andrew Trick 88bd8629b2 Allow MachineCSE to coalesce trivial subregister copies the same way
that it coalesces normal copies.

Without this, MachineCSE is powerless to handle redundant operations
with truncated source operands.

This required fixing the 2-addr pass to handle tied subregisters. It
isn't clear what combinations of subregisters can legally be tied, but
the simple case of truncated source operands is now safely handled:

     %vreg11<def> = COPY %vreg1:sub_32bit; GR32:%vreg11 GR64:%vreg1
     %vreg12<def> = COPY %vreg2:sub_32bit; GR32:%vreg12 GR64:%vreg2
     %vreg13<def,tied1> = ADD32rr %vreg11<tied0>, %vreg12<kill>, %EFLAGS<imp-def>

llvm-svn: 197414
2013-12-16 19:36:21 +00:00