From 01ef4c2c64e17f339d1ef9da992493c652be7f8e Mon Sep 17 00:00:00 2001 From: Hiroshi Inoue Date: Thu, 7 Jun 2018 13:21:14 +0000 Subject: [PowerPC] avoid unprofitable Repl32 flag in BitPermutationSelector BitPermutationSelector sets Repl32 flag for bit groups which can be (potentially) benefit from 32-bit rotate-and-mask instructions with bit replication, i.e. rlwinm/rlwimi copies lower 32 bits into upper 32 bits on 64-bit PowerPC before rotation. However, enforcing 32-bit instruction sometimes results in redundant generated code. For example, the following simple code is compiled into rotldi + rlwimi while it can be compiled into only rldimi instruction if Repl32 flag is not set on the bit group for (a & 0xFFFFFFFF). uint64_t func(uint64_t a, uint64_t b) { return (a & 0xFFFFFFFF) | (b << 32) ; } To avoid such problem, this patch checks the potential benefit of Repl32 flag before setting it. If a bit group does not require rotation (i.e. RLAmt == 0) and won't be merged into another group, we do not benefit from Repl32 flag on this group. Differential Revision: https://reviews.llvm.org/D47867 llvm-svn: 334195 --- llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'llvm/lib/Target') diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp index de2c2289251..4b0633142c1 100644 --- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp +++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp @@ -1450,6 +1450,20 @@ class BitPermutationSelector { }; for (auto &BG : BitGroups) { + // If this bit group has RLAmt of 0 and will not be merged with + // another bit group, we don't benefit from Repl32. We don't mark + // such group to give more freedom for later instruction selection. + if (BG.RLAmt == 0) { + auto PotentiallyMerged = [this](BitGroup & BG) { + for (auto &BG2 : BitGroups) + if (&BG != &BG2 && BG.V == BG2.V && + (BG2.RLAmt == 0 || BG2.RLAmt == 32)) + return true; + return false; + }; + if (!PotentiallyMerged(BG)) + continue; + } if (BG.StartIdx < 32 && BG.EndIdx < 32) { if (IsAllLow32(BG)) { if (BG.RLAmt >= 32) { -- cgit v1.2.3