PowerPC: Simplify FADD in round-to-zero mode.

As part of the the sequence generated to implement long double -> int
conversions, we need to perform an FADD in round-to-zero mode.  This is
problematical since the FPSCR is not at all modeled at the SelectionDAG
level, and thus there is a risk of getting floating point instructions
generated out of sequence with the instructions to modify FPSCR.

The current code handles this by somewhat "special" patterns that in part
have dummy operands, and/or duplicate existing instructions, making them
awkward to handle in the asm parser.

This commit changes this by leaving the "FADD in round-to-zero mode"
as an atomic operation on the SelectionDAG level, and only split it up into
real instructions at the MI level (via custom inserter).  Since at *this*
level the FPSCR *is* modeled (via the "RM" hard register), much of the
"special" stuff can just go away, and the resulting patterns can be used by
the asm parser.

No significant change in generated code expected.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178006 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 18 deletions

diff --git a/lib/Target/PowerPC/PPCISelLowering.h b/lib/Target/PowerPC/PPCISelLowering.h
index da438a5aa7..6296400ec7 100644
--- a/lib/Target/PowerPC/PPCISelLowering.h
+++ b/lib/Target/PowerPC/PPCISelLowering.h
@@ -142,26 +142,13 @@ namespace llvm {
       /// an optional input flag argument.
       COND_BRANCH,
 
-      // The following 5 instructions are used only as part of the
-      // long double-to-int conversion sequence.
-
-      /// OUTFLAG = MFFS F8RC - This moves the FPSCR (not modelled) into the
-      /// register.
-      MFFS,
-
-      /// OUTFLAG = MTFSB0 INFLAG - This clears a bit in the FPSCR.
-      MTFSB0,
-
-      /// OUTFLAG = MTFSB1 INFLAG - This sets a bit in the FPSCR.
-      MTFSB1,
-
-      /// F8RC, OUTFLAG = FADDRTZ F8RC, F8RC, INFLAG - This is an FADD done with
-      /// rounding towards zero.  It has flags added so it won't move past the
-      /// FPSCR-setting instructions.
+      /// F8RC = FADDRTZ F8RC, F8RC - This is an FADD done with rounding
+      /// towards zero.  Used only as part of the long double-to-int
+      /// conversion sequence.
       FADDRTZ,
 
-      /// MTFSF = F8RC, INFLAG - This moves the register into the FPSCR.
-      MTFSF,
+      /// F8RC = MFFS - This moves the FPSCR (not modeled) into the register.
+      MFFS,
 
       /// LARX = This corresponds to PPC l{w|d}arx instrcution: load and
       /// reserve indexed. This is used to implement atomic operations.