Handle non-~0 lane masks on live-in registers in LivePhysRegs

[kparzysz]

Summary

When LivePhysRegs adds live-in registers, it recognizes ~0 as a special lane mask indicating the entire register. If the lane mask is not ~0, it will only add the subregisters that overlap the specified lane mask. The problem is that if a live-in register does not have subregisters, and the lane mask is not ~0, it will not be added to the live set. (The given lane mask may simply be the lane mask of its register class.)
If a register does not have subregisters, add it to the live set if the lane mask is non-zero.

[MatzeB]

LGTM.

lib/CodeGen/LivePhysRegs.cpp

151–154 ↗

(On Diff #76234)

change this to a for ( ; S.isValid(); ++S) { ... } loop?

llvm/trunk/lib/CodeGen/LivePhysRegs.cpp

if (LiveRegs.count(*R))
       return false;
   }
   return true;
 }
 
 /// Add live-in registers of basic block \p MBB to \p LiveRegs.
 void LivePhysRegs::addBlockLiveIns(const MachineBasicBlock &MBB) {
   for (const auto &LI : MBB.liveins()) {
-    if (LI.LaneMask == ~0u) {
+    MCSubRegIndexIterator S(LI.PhysReg, TRI);
+    if (LI.LaneMask == ~0u || (LI.LaneMask != 0 && !S.isValid())) {
       addReg(LI.PhysReg);
       continue;
     }
-    for (MCSubRegIndexIterator S(LI.PhysReg, TRI); S.isValid(); ++S)
+    for (; S.isValid(); ++S)
       if (LI.LaneMask & TRI->getSubRegIndexLaneMask(S.getSubRegIndex()))
         addReg(S.getSubReg());
   }
 }
 
 /// Add pristine registers to the given \p LiveRegs. This function removes
 /// actually saved callee save registers when \p InPrologueEpilogue is false.
 static void addPristines(LivePhysRegs &LiveRegs, const MachineFunction &MF,

llvm/trunk/test/CodeGen/Hexagon/livephysregs-lane-masks2.mir

+# RUN: llc -march=hexagon -verify-machineinstrs -run-pass branch-folder -o - %s | FileCheck %s
+
+# CHECK-LABEL: name: fred
+
+--- |
+  define void @fred() { ret void }
+
+...
+---
+
+name: fred
+tracksRegLiveness: true
+
+body: |
+  bb.0:
+    liveins: %p2, %r0
+    successors: %bb.1, %bb.2
+        J2_jumpt killed %p2, %bb.1, implicit-def %pc
+        J2_jump %bb.2, implicit-def %pc
+
+  bb.1:
+    liveins: %r0, %r19
+    successors: %bb.3
+        %r2 = A2_tfrsi 4
+        %r1 = COPY %r19
+        %r0 = S2_asl_r_r killed %r0, killed %r2
+        %r0 = A2_asrh killed %r0
+        J2_jump %bb.3, implicit-def %pc
+
+  bb.2:
+    liveins: %r0, %r18
+    successors: %bb.3
+        %r2 = A2_tfrsi 5
+        %r1 = L2_loadrh_io %r18, 0
+        %r0 = S2_asl_r_r killed %r0, killed %r2
+        %r0 = A2_asrh killed %r0
+
+  bb.3:
+    ; A live-in register without subregs, but with a lane mask that is not ~0
+    ; is not recognized by LivePhysRegs. Branch folding exposes this problem
+    ; (through tail merging).
+    ;
+    ; CHECK: bb.3:
+    ; CHECK: liveins:{{.*}}%p0
+    ; CHECK:   %r0 = S2_asl_r_r killed %r0, killed %r2
+    ; CHECK:   %r0 = A2_asrh killed %r0
+    ; CHECK:   %r0 = C2_cmoveit killed %p0, 1
+    ; CHECK:   J2_jumpr %r31, implicit-def %pc, implicit %r0
+    ;
+    liveins: %p0:0x1
+        %r0 = C2_cmoveit killed %p0, 1
+        J2_jumpr %r31, implicit-def %pc, implicit %r0
+...
+
+