[llvm] r292871 - LiveIntervalAnalysis: Calculate liveness even if a superreg is reserved.

[Matthias Braun via llvm-commits]

Author: matze
Date: Mon Jan 23 19:12:58 2017
New Revision: 292871

URL: http://llvm.org/viewvc/llvm-project?rev=292871&view=rev
Log:
LiveIntervalAnalysis: Calculate liveness even if a superreg is reserved.

A register unit may be allocatable and non-reserved but some of the
register(tuples) built with it are reserved. We still need to calculate
liveness in this case.

Note to out of tree targets: If you start seeing machine verifier errors
with this commit, it probably means that you do not properly mark super
registers of reserved register as reserved. See for example r292836 or
r292870 for example on how to fix that.

rdar://29996737

Differential Revision: https://reviews.llvm.org/D28881

Added:
    llvm/trunk/test/CodeGen/AArch64/live-interval-analysis.mir
Modified:
    llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp

Modified: llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp?rev=292871&r1=292870&r2=292871&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp (original)
+++ llvm/trunk/lib/CodeGen/LiveIntervalAnalysis.cpp Mon Jan 23 19:12:58 2017
@@ -253,23 +253,30 @@ void LiveIntervals::computeRegUnitRange(
   // may share super-registers. That's OK because createDeadDefs() is
   // idempotent. It is very rare for a register unit to have multiple roots, so
   // uniquing super-registers is probably not worthwhile.
+  bool IsReserved = true;
   for (MCRegUnitRootIterator Root(Unit, TRI); Root.isValid(); ++Root) {
     for (MCSuperRegIterator Super(*Root, TRI, /*IncludeSelf=*/true);
          Super.isValid(); ++Super) {
       unsigned Reg = *Super;
       if (!MRI->reg_empty(Reg))
         LRCalc->createDeadDefs(LR, Reg);
+      // A register unit is considered reserved if all its roots and all their
+      // super registers are reserved.
+      if (!MRI->isReserved(Reg))
+        IsReserved = false;
     }
   }
 
   // Now extend LR to reach all uses.
   // Ignore uses of reserved registers. We only track defs of those.
-  for (MCRegUnitRootIterator Root(Unit, TRI); Root.isValid(); ++Root) {
-    for (MCSuperRegIterator Super(*Root, TRI, /*IncludeSelf=*/true);
-         Super.isValid(); ++Super) {
-      unsigned Reg = *Super;
-      if (!MRI->isReserved(Reg) && !MRI->reg_empty(Reg))
-        LRCalc->extendToUses(LR, Reg);
+  if (!IsReserved) {
+    for (MCRegUnitRootIterator Root(Unit, TRI); Root.isValid(); ++Root) {
+      for (MCSuperRegIterator Super(*Root, TRI, /*IncludeSelf=*/true);
+           Super.isValid(); ++Super) {
+        unsigned Reg = *Super;
+        if (!MRI->reg_empty(Reg))
+          LRCalc->extendToUses(LR, Reg);
+      }
     }
   }
 

Added: llvm/trunk/test/CodeGen/AArch64/live-interval-analysis.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/live-interval-analysis.mir?rev=292871&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/AArch64/live-interval-analysis.mir (added)
+++ llvm/trunk/test/CodeGen/AArch64/live-interval-analysis.mir Mon Jan 23 19:12:58 2017
@@ -0,0 +1,22 @@
+# RUN: llc -o /dev/null %s -mtriple=aarch64-darwin-ios -run-pass=liveintervals -debug-only=regalloc -precompute-phys-liveness 2>&1 | FileCheck %s
+# REQUIRES: asserts
+--- |
+  define void @reserved_reg_liveness() { ret void }
+...
+---
+# CHECK-LABEL: ********** INTERVALS **********
+# W29 is reserved, so we should only see dead defs
+# CHECK-DAG: W29 [0B,0d:{{[0-9]+}})[32r,32d:{{[0-9]+}})[64r,64d:{{[0-9]+}})
+# For normal registers like x28 we should see the full intervals
+# CHECK-DAG: W28 [0B,16r:{{[0-9]+}})[32r,48r:{{[0-9]+}})[48r,48d:{{[0-9]+}})
+# CHECK: # End machine code for function reserved_reg_liveness.
+name: reserved_reg_liveness
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: %x28_fp
+    %6 : xseqpairsclass = COPY %x28_fp
+    %x28_fp = COPY %6
+    %x28 = COPY %x28
+    %fp = COPY %fp
+...