[PowerPC] Remove zexts after byte-swapping loads

lhbrx and lwbrx not only load their data with byte swapping, but also clear the
upper 32 bits (at least). As a result, they can be added to the PPCISelDAGToDAG
peephole optimization as frontier instructions for the removal of unnecessary
zero extensions.

llvm-svn: 225189

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/PowerPC/rm-zext.ll b/llvm/test/CodeGen/PowerPC/rm-zext.ll
index 8fab38ad4cf..291b7919280 100644
--- a/llvm/test/CodeGen/PowerPC/rm-zext.ll
+++ b/llvm/test/CodeGen/PowerPC/rm-zext.ll
@@ -39,5 +39,35 @@ entry:
 ; CHECK: blr
 }
 
+; Function Attrs: nounwind readnone
+declare i32 @llvm.bswap.i32(i32) #1
+
+; Function Attrs: nounwind readonly
+define zeroext i32 @bs32(i32* nocapture readonly %x) #0 {
+entry:
+  %0 = load i32* %x, align 4
+  %1 = tail call i32 @llvm.bswap.i32(i32 %0)
+  ret i32 %1
+
+; CHECK-LABEL: @bs32
+; CHECK-NOT: rldicl 3, {{[0-9]+}}, 0, 32
+; CHECK: blr
+}
+
+; Function Attrs: nounwind readonly
+define zeroext i16 @bs16(i16* nocapture readonly %x) #0 {
+entry:
+  %0 = load i16* %x, align 2
+  %1 = tail call i16 @llvm.bswap.i16(i16 %0)
+  ret i16 %1
+
+; CHECK-LABEL: @bs16
+; CHECK-NOT: rldicl 3, {{[0-9]+}}, 0, 32
+; CHECK: blr
+}
+
+; Function Attrs: nounwind readnone
+declare i16 @llvm.bswap.i16(i16) #1
+
 attributes #0 = { nounwind readnone }