LiveIntervalAnalysis: Rework constructMainRangeFromSubranges()

We now use LiveRangeCalc::extendToUses() instead of a specially designed
algorithm in constructMainRangeFromSubranges():
- The original motivation for constructMainRangeFromSubranges() were
  differences between the main liverange and subranges because of hidden
  dead definitions. This case however cannot happen anymore with the
  DetectDeadLaneMasks pass in place.
- It simplifies the code.
- This fixes a longstanding bug where we did not properly create new SSA
  values on merging control flow (the MachineVerifier missed most of
  these cases).
- Move constructMainRangeFromSubranges() to LiveIntervalAnalysis and
  LiveRangeCalc to better match the implementation/available helper
  functions.

This re-applies r269016. The fixes from r270290 and r270259 should avoid
the machine verifier problems this time.

llvm-svn: 270291

1 files changed, 32 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/AMDGPU/liveness.mir b/llvm/test/CodeGen/AMDGPU/liveness.mir
new file mode 100644
index 00000000000..ce49294d5b3
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/liveness.mir
@@ -0,0 +1,32 @@
+# RUN: llc -march=amdgcn -run-pass liveintervals -verify-machineinstrs -o /dev/null -debug-only=regalloc %s 2>&1 | FileCheck %s
+# REQUIRES: asserts
+# We currently maintain a main liveness range which operates like a superset of
+# all subregister liveranges. We may need to create additional SSA values at
+# merge point in this main liverange even though none of the subregister
+# liveranges needed it.
+#
+# Should see three distinct value numbers:
+# CHECK: %vreg0 [{{.*}}:0)[{{.*}}:1)[{{.*}}:2) 0@{{[0-9]+[Berd]}} 1@{{[0-9]+[Berd]}} 2@{{[0-9]+B-phi}}
+--- |
+  define void @test0() { ret void }
+...
+---
+name: test0
+registers:
+  - { id: 0, class: sreg_64 }
+body: |
+  bb.0:
+    successors: %bb.1, %bb.2
+    S_NOP 0, implicit-def undef %0:sub0
+    S_CBRANCH_VCCNZ %bb.1, implicit undef %vcc
+    S_BRANCH %bb.2
+
+  bb.1:
+    successors: %bb.2
+    S_NOP 0, implicit-def %0:sub1
+    S_NOP 0, implicit %0:sub1
+    S_BRANCH %bb.2
+
+  bb.2:
+    S_NOP 0, implicit %0:sub0
+...