[llvm] r358983 - AMDGPU: Fix LCSSA phi lowering in SILowerI1Copies

[Nicolai Haehnle via llvm-commits]

Author: nha
Date: Tue Apr 23 06:12:52 2019
New Revision: 358983

URL: http://llvm.org/viewvc/llvm-project?rev=358983&view=rev
Log:
AMDGPU: Fix LCSSA phi lowering in SILowerI1Copies

Summary:
When an LCSSA phi survives through instruction selection, the pass
ends up removing that phi entirely because it is dominated by the
logic that does the lanemask merging.

This then used to trigger an assertion when processing a dependent
phi instruction.

Change-Id: Id4949719f8298062fe476a25718acccc109113b6

Reviewers: llvm-commits

Subscribers: kzhuravl, jvesely, wdng, yaxunl, t-tye, tpr, dstuttard, rtaylor, arsenm

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60999

Added:
    llvm/trunk/test/CodeGen/AMDGPU/si-lower-i1-copies.mir
Modified:
    llvm/trunk/lib/Target/AMDGPU/SILowerI1Copies.cpp

Modified: llvm/trunk/lib/Target/AMDGPU/SILowerI1Copies.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AMDGPU/SILowerI1Copies.cpp?rev=358983&r1=358982&r2=358983&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AMDGPU/SILowerI1Copies.cpp (original)
+++ llvm/trunk/lib/Target/AMDGPU/SILowerI1Copies.cpp Tue Apr 23 06:12:52 2019
@@ -504,6 +504,9 @@ void SILowerI1Copies::lowerPhis() {
   SmallVector<MachineBasicBlock *, 4> IncomingBlocks;
   SmallVector<unsigned, 4> IncomingRegs;
   SmallVector<unsigned, 4> IncomingUpdated;
+#ifndef NDEBUG
+  DenseSet<unsigned> PhiRegisters;
+#endif
 
   for (MachineBasicBlock &MBB : *MF) {
     LF.initialize(MBB);
@@ -531,13 +534,17 @@ void SILowerI1Copies::lowerPhis() {
         } else if (IncomingDef->getOpcode() == AMDGPU::IMPLICIT_DEF) {
           continue;
         } else {
-          assert(IncomingDef->isPHI());
+          assert(IncomingDef->isPHI() || PhiRegisters.count(IncomingReg));
         }
 
         IncomingBlocks.push_back(IncomingMBB);
         IncomingRegs.push_back(IncomingReg);
       }
 
+#ifndef NDEBUG
+      PhiRegisters.insert(DstReg);
+#endif
+
       // Phis in a loop that are observed outside the loop receive a simple but
       // conservatively correct treatment.
       MachineBasicBlock *PostDomBound = &MBB;

Added: llvm/trunk/test/CodeGen/AMDGPU/si-lower-i1-copies.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AMDGPU/si-lower-i1-copies.mir?rev=358983&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/AMDGPU/si-lower-i1-copies.mir (added)
+++ llvm/trunk/test/CodeGen/AMDGPU/si-lower-i1-copies.mir Tue Apr 23 06:12:52 2019
@@ -0,0 +1,33 @@
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -verify-machineinstrs -run-pass=si-i1-copies -o - %s | FileCheck -check-prefixes=GCN %s
+
+# GCN-LABEL: name: lcssa_phi
+---
+name:              lcssa_phi
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    %0:sreg_64 = S_MOV_B64 0
+    %8:vreg_1 = IMPLICIT_DEF
+    %10:sreg_64 = IMPLICIT_DEF
+    %11:sreg_64 = SI_IF %10, %bb.3, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+    S_BRANCH %bb.1
+
+  bb.1:
+    %1:sreg_64 = PHI %0, %bb.0, %3, %bb.1
+    %2:sreg_64 = IMPLICIT_DEF
+    %3:sreg_64 = SI_IF_BREAK %2, %1, implicit-def dead $scc
+    %4:sreg_64 = IMPLICIT_DEF
+    %5:vreg_1 = COPY %4
+    SI_LOOP %3, %bb.1, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+    S_BRANCH %bb.2
+
+  bb.2:
+    %6:vreg_1 = PHI %5, %bb.1
+    SI_END_CF %3, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+
+  bb.3:
+    %7:vreg_1 = PHI %6, %bb.2, %8, %bb.0
+    SI_END_CF %11, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+    S_ENDPGM 0
+
+...