[llvm] 36f9fe2 - [PowerPC] fixupIsDeadOrKill start and end in different block fixing

[Chen Zheng via llvm-commits]

Author: Chen Zheng
Date: 2020-07-22T06:27:13-04:00
New Revision: 36f9fe2d3493717dbc6866d96b2e989839ce1a4c

URL: https://github.com/llvm/llvm-project/commit/36f9fe2d3493717dbc6866d96b2e989839ce1a4c
DIFF: https://github.com/llvm/llvm-project/commit/36f9fe2d3493717dbc6866d96b2e989839ce1a4c.diff

LOG: [PowerPC] fixupIsDeadOrKill start and end in different block fixing

In fixupIsDeadOrKill, we assume StartMI and EndMI not exist in same
basic block, so we add an assertion in that function. This is wrong
before RA, as before RA the true definition may exist in another
block through copy like instructions.

Reviewed By: nemanjai

Differential Revision: https://reviews.llvm.org/D83365

Added: 
    llvm/test/CodeGen/PowerPC/fixup-kill-dead-flag-crash.mir

Modified: 
    llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
    llvm/lib/Target/PowerPC/PPCInstrInfo.h

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index 269a74a18676..6b822a803132 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -2668,6 +2668,15 @@ const unsigned *PPCInstrInfo::getLoadOpcodesForSpillArray() const {
 
 void PPCInstrInfo::fixupIsDeadOrKill(MachineInstr &StartMI, MachineInstr &EndMI,
                                      unsigned RegNo) const {
+  // Conservatively clear kill flag for the register if the instructions are in
+  // 
diff erent basic blocks and in SSA form, because the kill flag may no longer
+  // be right. There is no need to bother with dead flags since defs with no
+  // uses will be handled by DCE.
+  MachineRegisterInfo &MRI = StartMI.getParent()->getParent()->getRegInfo();
+  if (MRI.isSSA() && (StartMI.getParent() != EndMI.getParent())) {
+    MRI.clearKillFlags(RegNo);
+    return;
+  }
 
   // Instructions between [StartMI, EndMI] should be in same basic block.
   assert((StartMI.getParent() == EndMI.getParent()) &&

diff  --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.h b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
index d98597f48340..43973c627fcf 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.h
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.h
@@ -565,14 +565,18 @@ class PPCInstrInfo : public PPCGenInstrInfo {
                              int64_t OffsetImm) const;
 
   /// Fixup killed/dead flag for register \p RegNo between instructions [\p
-  /// StartMI, \p EndMI]. Some PostRA transformations may violate register
-  /// killed/dead flags semantics, this function can be called to fix up. Before
-  /// calling this function,
+  /// StartMI, \p EndMI]. Some pre-RA or post-RA transformations may violate
+  /// register killed/dead flags semantics, this function can be called to fix
+  /// up. Before calling this function,
   /// 1. Ensure that \p RegNo liveness is killed after instruction \p EndMI.
   /// 2. Ensure that there is no new definition between (\p StartMI, \p EndMI)
   ///    and possible definition for \p RegNo is \p StartMI or \p EndMI.
-  /// 3. Ensure that all instructions between [\p StartMI, \p EndMI] are in same
-  ///    basic block.
+  /// 3. We can do accurate fixup for the case when all instructions between
+  ///    [\p StartMI, \p EndMI] are in same basic block.
+  /// 4. For the case when \p StartMI and \p EndMI are not in same basic block,
+  ///    we conservatively clear kill flag for all uses of \p RegNo for pre-RA
+  ///    and for post-RA, we give an assertion as without reaching definition
+  ///    analysis post-RA, \p StartMI and \p EndMI are hard to keep right.
   void fixupIsDeadOrKill(MachineInstr &StartMI, MachineInstr &EndMI,
                          unsigned RegNo) const;
   void replaceInstrWithLI(MachineInstr &MI, const LoadImmediateInfo &LII) const;

diff  --git a/llvm/test/CodeGen/PowerPC/fixup-kill-dead-flag-crash.mir b/llvm/test/CodeGen/PowerPC/fixup-kill-dead-flag-crash.mir
new file mode 100644
index 000000000000..be2671fa9b5d
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/fixup-kill-dead-flag-crash.mir
@@ -0,0 +1,21 @@
+# RUN: llc -mtriple=powerpc64le-unknown-linux-gnu -verify-machineinstrs -start-before ppc-mi-peepholes \
+# RUN:   -stop-after ppc-mi-peepholes %s -o - | FileCheck %s
+
+---
+name: test
+#CHECK : name : test
+tracksRegLiveness: true
+body: |
+  bb.0.entry:
+    liveins: $x3
+    %0:g8rc = COPY $x3
+    %1:gprc = COPY %0.sub_32:g8rc
+    %2:g8rc = LI8 63
+
+  bb.1:
+    %3:gprc = COPY %2.sub_32:g8rc
+    ; CHECK: %4:gprc = LI 0
+    %4:gprc = XORI killed %3:gprc, 63
+    STW killed %4:gprc, %4:gprc, 100
+    BLR8 implicit $lr8, implicit $rm
+...