[PowerPC] Sign extend sub-word values for atomic comparisons

Atomic comparison instructions use the sub-word load instruction on
Power8 and up but the value is not sign extended prior to the signed word
compare instruction. This patch adds that sign extension.

llvm-svn: 282182

Author: nemanjai

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -8507,8 +8507,17 @@ PPCTargetLowering::EmitAtomicBinary(MachineInstr &MI, MachineBasicBlock *BB,
   if (BinOpcode)
     BuildMI(BB, dl, TII->get(BinOpcode), TmpReg).addReg(incr).addReg(dest);
   if (CmpOpcode) {
-    BuildMI(BB, dl, TII->get(CmpOpcode), PPC::CR0)
-      .addReg(incr).addReg(dest);
+    // Signed comparisons of byte or halfword values must be sign-extended.
+    if (CmpOpcode == PPC::CMPW && AtomicSize < 4) {
+      unsigned ExtReg =  RegInfo.createVirtualRegister(&PPC::GPRCRegClass);
+      BuildMI(BB, dl, TII->get(AtomicSize == 1 ? PPC::EXTSB : PPC::EXTSH),
+              ExtReg).addReg(dest);
+      BuildMI(BB, dl, TII->get(CmpOpcode), PPC::CR0)
+        .addReg(incr).addReg(ExtReg);
+    } else
+      BuildMI(BB, dl, TII->get(CmpOpcode), PPC::CR0)
+        .addReg(incr).addReg(dest);
+
     BuildMI(BB, dl, TII->get(PPC::BCC))
       .addImm(CmpPred).addReg(PPC::CR0).addMBB(exitMBB);
     BB->addSuccessor(loop2MBB);

llvm/test/CodeGen/PowerPC/pr30451.ll

@@ -0,0 +1,69 @@
+; RUN: llc < %s -mcpu=pwr8 -mtriple=powerpc64le-unknown-unknown | FileCheck %s
+define i8 @atomic_min_i8() {
+    top:
+      %0 = alloca i8, align 2
+      %1 = bitcast i8* %0 to i8*
+      call void @llvm.lifetime.start(i64 2, i8* %1)
+      store i8 -1, i8* %0, align 2
+      %2 = atomicrmw min i8* %0, i8 0 acq_rel
+      %3 = load atomic i8, i8* %0 acquire, align 8
+      call void @llvm.lifetime.end(i64 2, i8* %1)
+      ret i8 %3
+; CHECK-LABEL: atomic_min_i8
+; CHECK: lbarx [[DST:[0-9]+]],
+; CHECK-NEXT: extsb [[EXT:[0-9]+]], [[DST]]
+; CHECK-NEXT: cmpw {{[0-9]+}}, [[EXT]]
+; CHECK-NEXT: bge 0
+}
+define i16 @atomic_min_i16() {
+    top:
+      %0 = alloca i16, align 2
+      %1 = bitcast i16* %0 to i8*
+      call void @llvm.lifetime.start(i64 2, i8* %1)
+      store i16 -1, i16* %0, align 2
+      %2 = atomicrmw min i16* %0, i16 0 acq_rel
+      %3 = load atomic i16, i16* %0 acquire, align 8
+      call void @llvm.lifetime.end(i64 2, i8* %1)
+      ret i16 %3
+; CHECK-LABEL: atomic_min_i16
+; CHECK: lharx [[DST:[0-9]+]],
+; CHECK-NEXT: extsh [[EXT:[0-9]+]], [[DST]]
+; CHECK-NEXT: cmpw {{[0-9]+}}, [[EXT]]
+; CHECK-NEXT: bge 0
+}
+
+define i8 @atomic_max_i8() {
+    top:
+      %0 = alloca i8, align 2
+      %1 = bitcast i8* %0 to i8*
+      call void @llvm.lifetime.start(i64 2, i8* %1)
+      store i8 -1, i8* %0, align 2
+      %2 = atomicrmw max i8* %0, i8 0 acq_rel
+      %3 = load atomic i8, i8* %0 acquire, align 8
+      call void @llvm.lifetime.end(i64 2, i8* %1)
+      ret i8 %3
+; CHECK-LABEL: atomic_max_i8
+; CHECK: lbarx [[DST:[0-9]+]],
+; CHECK-NEXT: extsb [[EXT:[0-9]+]], [[DST]]
+; CHECK-NEXT: cmpw {{[0-9]+}}, [[EXT]]
+; CHECK-NEXT: ble 0
+}
+define i16 @atomic_max_i16() {
+    top:
+      %0 = alloca i16, align 2
+      %1 = bitcast i16* %0 to i8*
+      call void @llvm.lifetime.start(i64 2, i8* %1)
+      store i16 -1, i16* %0, align 2
+      %2 = atomicrmw max i16* %0, i16 0 acq_rel
+      %3 = load atomic i16, i16* %0 acquire, align 8
+      call void @llvm.lifetime.end(i64 2, i8* %1)
+      ret i16 %3
+; CHECK-LABEL: atomic_max_i16
+; CHECK: lharx [[DST:[0-9]+]],
+; CHECK-NEXT: extsh [[EXT:[0-9]+]], [[DST]]
+; CHECK-NEXT: cmpw {{[0-9]+}}, [[EXT]]
+; CHECK-NEXT: ble 0
+}
+
+declare void @llvm.lifetime.start(i64, i8*)
+declare void @llvm.lifetime.end(i64, i8*)