[MachineOutliner] Outline both register save calls + no LR save calls together

Instead of treating the outlined functions for these as distinct frames, they
should be combined into one case. Neither allows for stack fixups, and both
generate the same frame. Thus, they ought to be considered one case.

This makes the code far easier to understand, for one thing. It also offers
some small code size improvements. It's fairly rare to see a class of outlined
functions that doesn't fall entirely into one variant (on CTMark anyway). It
does happen from time to time though.

This mostly offers some serious simplification.

Also update the test to show the added functionality.

llvm-svn: 348036

llvm/lib/Target/AArch64/AArch64InstrInfo.cpp

@@ -5165,42 +5165,36 @@ AArch64InstrInfo::getOutliningCandidateInfo(
     SetCandidateCallInfo(MachineOutlinerThunk, 4);
   }
 
-  // Make sure that LR isn't live on entry to this candidate. The only
-  // instructions that use LR that could possibly appear in a repeated sequence
-  // are calls. Therefore, we only have to check and see if LR is dead on entry
-  // to (or exit from) some candidate.
-  else if (std::all_of(RepeatedSequenceLocs.begin(),
-                       RepeatedSequenceLocs.end(),
-                       [&TRI](outliner::Candidate &C) {
-                         C.initLRU(TRI);
-                         return C.LRU.available(AArch64::LR);
-                         })) {
-    FrameID = MachineOutlinerNoLRSave;
-    NumBytesToCreateFrame = 4;
-    SetCandidateCallInfo(MachineOutlinerNoLRSave, 4);
-  }
-
-  // LR is live, so we need to save it. Decide whether it should be saved to
-  // the stack, or if it can be saved to a register.
   else {
-    if (all_of(RepeatedSequenceLocs, [this, &TRI](outliner::Candidate &C) {
-          C.initLRU(TRI);
-          return findRegisterToSaveLRTo(C);
-        })) {
-      // Every candidate has an available callee-saved register for the save.
-      // We can save LR to a register.
-      FrameID = MachineOutlinerRegSave;
-      NumBytesToCreateFrame = 4;
-      SetCandidateCallInfo(MachineOutlinerRegSave, 12);
+    // We need to decide how to emit calls + frames. We can always emit the same
+    // frame if we don't need to save to the stack. If we have to save to the
+    // stack, then we need a different frame.
+    unsigned NumNoStackSave = 0;
+
+    for (outliner::Candidate &C : RepeatedSequenceLocs) {
+      C.initLRU(TRI);
+
+      // Is LR available? If so, we don't need a save.
+      if (C.LRU.available(AArch64::LR)) {
+        C.setCallInfo(MachineOutlinerNoLRSave, 4);
+        ++NumNoStackSave;
+      }
+
+      // Is an unused register available? If so, we won't modify the stack, so
+      // we can outline with the same frame type as those that don't save LR.
+      else if (findRegisterToSaveLRTo(C)) {
+        C.setCallInfo(MachineOutlinerRegSave, 12);
+        ++NumNoStackSave;
+      }
     }
 
-    else {
-      // At least one candidate does not have an available callee-saved
-      // register. We must save LR to the stack.
-      FrameID = MachineOutlinerDefault;
-      NumBytesToCreateFrame = 4;
+    // If there are no places where we have to save LR, then note that we don't
+    // have to update the stack. Otherwise, give every candidate the default
+    // call type.
+    if (NumNoStackSave == RepeatedSequenceLocs.size())
+      FrameID = MachineOutlinerNoLRSave;
+    else
       SetCandidateCallInfo(MachineOutlinerDefault, 12);
-    }
   }
 
   // Does every candidate's MBB contain a call? If so, then we might have a call

llvm/test/CodeGen/AArch64/machine-outliner-regsave.mir

@@ -2,8 +2,8 @@
 # RUN: -run-pass=machine-outliner -verify-machineinstrs %s -o - | FileCheck %s
 # Check that we save LR to a callee-saved register when possible.
 # foo() should use a callee-saved register. However, bar() should not.
---- |  
-  
+--- |
+
   define void @foo() #0 {
     ret void
   }
@@ -17,32 +17,31 @@
 ---
 # Make sure that when we outline and a register is available, we
 # use it to save + restore LR instead of SP.
+# Also make sure that we can call functions that require no save as the same
+# outlined function.
 # CHECK: name:            foo
-# CHECK-DAG: bb.0
-# CHECK-DAG: $x[[REG:[0-9]+]] = ORRXrs $xzr, $lr, 0
-# CHECK-NEXT: BL
-# CHECK-NEXT: $lr = ORRXrs $xzr, $x[[REG]], 0
 # CHECK-DAG: bb.1
-# CHECK-DAG: $x[[REG]] = ORRXrs $xzr, $lr, 0
+# CHECK-DAG: $x[[REG:[0-9]+]] = ORRXrs $xzr, $lr, 0
 # CHECK-NEXT: BL
 # CHECK-NEXT: $lr = ORRXrs $xzr, $x[[REG]], 0
 # CHECK-DAG: bb.2
 # CHECK-DAG: $x[[REG]] = ORRXrs $xzr, $lr, 0
 # CHECK-NEXT: BL
 # CHECK-NEXT: $lr = ORRXrs $xzr, $x[[REG]], 0
+# CHECK-DAG: bb.3
+# CHECK-DAG: $x[[REG]] = ORRXrs $xzr, $lr, 0
+# CHECK-NEXT: BL
+# CHECK-NEXT: $lr = ORRXrs $xzr, $x[[REG]], 0
+# CHECK-DAG: bb.4
+# CHECK-NOT: $x[[REG]] = ORRXrs $xzr, $lr, 0
+# CHECK-DAG: BL
 name:            foo
 tracksRegLiveness: true
-fixedStack:      
+fixedStack:
 body:             |
   bb.0:
-    liveins: $lr, $w9
     $x25 = ORRXri $xzr, 1
-    $w9 = ORRWri $wzr, 1
-    $w9 = ORRWri $wzr, 1
-    $w9 = ORRWri $wzr, 1
-    $w9 = ORRWri $wzr, 1
-    $w9 = ORRWri $wzr, 1
-    $w9 = ORRWri $wzr, 2
+    $lr = ORRXri $xzr, 1
   bb.1:
     liveins: $lr, $w9
     $w9 = ORRWri $wzr, 1
@@ -59,6 +58,24 @@ body:             |
     $w9 = ORRWri $wzr, 1
     $w9 = ORRWri $wzr, 1
     $w9 = ORRWri $wzr, 2
+  bb.3:
+    liveins: $lr, $w9
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 2
+  bb.4:
+    liveins: $lr, $w9
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 1
+    $w9 = ORRWri $wzr, 2
+  bb.5:
+    liveins: $w9
     RET undef $lr
 
 ...
@@ -109,4 +126,3 @@ body:             |
   bb.3:
     liveins: $lr, $x0, $x1, $x2, $x3, $x4, $x5, $x6, $x7, $x8, $x9, $x10, $x11, $x12, $x13, $x14, $x15, $x19, $x20, $x21, $x22, $x23, $x20, $x21, $x22, $x23, $x24, $x25, $x26, $x27, $x28
     RET undef $lr
-