[PATCH] D67634: Remove assert from MachineLoop::getLoopPredecessor()

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec created this revision.
rampitec added reviewers: arsenm, kzhuravl.
Herald added subscribers: nhaehnle, wdng, jvesely.
Herald added a project: LLVM.

According to the documentation method returns predecessor
if the given loop's header has exactly one unique predecessor
outside the loop. Otherwise return null.

In reality it asserts if there is no predecessor outside of
the loop.

The testcase has the loop where predecessors outside of the
loop were not identified as analyzeBranch() was unable to
process the mask branch and returned true. That is also not
correct to assert for the truly dead loops.


https://reviews.llvm.org/D67634

Files:
  llvm/include/llvm/Analysis/LoopInfoImpl.h
  llvm/test/CodeGen/AMDGPU/loop_header_nopred.mir


Index: llvm/test/CodeGen/AMDGPU/loop_header_nopred.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AMDGPU/loop_header_nopred.mir
@@ -0,0 +1,55 @@
+# RUN: llc -march=amdgcn -o - -run-pass=block-placement -mcpu=gfx1010 -mattr=-inst-fwd-prefetch-bug -verify-machineinstrs %s | FileCheck -check-prefix=GCN %s
+
+# Used to fail with
+# Assertion `Out && "Header of loop has no predecessors from outside loop?"
+
+# GCN: name: loop_header_nopred
+# GCN: S_ENDPGM
+---
+name:            loop_header_nopred
+body:             |
+  bb.0:
+    successors: %bb.1(0x80000000)
+
+  bb.1:
+    successors: %bb.2(0x40000000), %bb.3(0x40000000)
+
+    S_CBRANCH_VCCZ %bb.3, implicit $vcc
+    S_BRANCH %bb.2
+
+  bb.2:
+    successors: %bb.3(0x80000000)
+
+  bb.3:
+    successors: %bb.4(0x40000000), %bb.6(0x40000000)
+
+    SI_MASK_BRANCH %bb.6, implicit $exec
+    S_BRANCH %bb.4
+
+  bb.4:
+    successors: %bb.5(0x04000000), %bb.4(0x7c000000)
+
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_NOP 0
+    S_CBRANCH_EXECZ %bb.4, implicit $exec
+
+  bb.5:
+    successors: %bb.6(0x80000000)
+
+  bb.6:
+    successors: %bb.7(0x04000000), %bb.1(0x7c000000)
+
+    S_CBRANCH_VCCZ %bb.1, implicit $vcc
+
+  bb.7:
+    S_ENDPGM 0
+...
Index: llvm/include/llvm/Analysis/LoopInfoImpl.h
===================================================================
--- llvm/include/llvm/Analysis/LoopInfoImpl.h
+++ llvm/include/llvm/Analysis/LoopInfoImpl.h
@@ -200,8 +200,6 @@
     }
   }
 
-  // Make sure there is only one exit out of the preheader.
-  assert(Out && "Header of loop has no predecessors from outside loop?");
   return Out;
 }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D67634.220388.patch
Type: text/x-patch
Size: 1765 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190916/eb4e4a54/attachment-0001.bin>