[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
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index de2c228..4b06331 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -1450,6 +1450,20 @@
};
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) {