[llvm] r350586 - [RegisterCoalescer] dst register's live interval needs to be updated when

[Wei Mi via llvm-commits]

Author: wmi
Date: Mon Jan  7 16:26:11 2019
New Revision: 350586

URL: http://llvm.org/viewvc/llvm-project?rev=350586&view=rev
Log:
[RegisterCoalescer] dst register's live interval needs to be updated when
merging a src register in ToBeUpdated set.

This is to fix PR40061 related with https://reviews.llvm.org/rL339035.

In https://reviews.llvm.org/rL339035, live interval of source pseudo register
in rematerialized copy may be saved in ToBeUpdated set and its update may be
postponed.

In PR40061, %t2 = %t1 is rematerialized and %t1 is added into toBeUpdated set
to postpone its live interval update. After the rematerialization, the live
interval of %t1 is larger than necessary. Then %t1 is merged into %t3 and %t1
gets removed. After the merge, %t3 contains live interval larger than necessary.
Because %t3 is not in toBeUpdated set, its live interval is not updated after
register coalescing and it will break some assumption in regalloc.

The patch requires the live interval of destination register in a merge to be
updated if the source register is in ToBeUpdated.

Differential revision: https://reviews.llvm.org/D55867


Added:
    llvm/trunk/test/CodeGen/X86/late-remat-update-2.mir
Modified:
    llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp

Modified: llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp?rev=350586&r1=350585&r2=350586&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp Mon Jan  7 16:26:11 2019
@@ -1910,6 +1910,13 @@ bool RegisterCoalescer::joinCopy(Machine
     }
     LI.removeEmptySubRanges();
   }
+
+  // CP.getSrcReg()'s live interval has been merged into CP.getDstReg's live
+  // interval. Since CP.getSrcReg() is in ToBeUpdated set and its live interval
+  // is not up-to-date, need to update the merged live interval here.
+  if (ToBeUpdated.count(CP.getSrcReg()))
+    ShrinkMainRange = true;
+
   if (ShrinkMainRange) {
     LiveInterval &LI = LIS->getInterval(CP.getDstReg());
     shrinkToUses(&LI);

Added: llvm/trunk/test/CodeGen/X86/late-remat-update-2.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/late-remat-update-2.mir?rev=350586&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/late-remat-update-2.mir (added)
+++ llvm/trunk/test/CodeGen/X86/late-remat-update-2.mir Mon Jan  7 16:26:11 2019
@@ -0,0 +1,63 @@
+# RUN: llc -mtriple=x86_64-- -run-pass=simple-register-coalescing -run-pass=regallocbasic -run-pass=virtregrewriter -late-remat-update-threshold=0 %s -o - | FileCheck %s
+#
+# PR40061: %t2 = %t1 is rematerialized and %t1 is added into toBeUpdated set
+# to postpone its live interval update. After the rematerialization, the live
+# interval of %t1 is larger than necessary. Then %t1 is merged into %t3 and %t1
+# gets removed. After the merge, %t3 contains live interval larger than
+# necessary. Because %t3 is not in toBeUpdated set so its live interval is not
+# updated after register coalescing, and it will break some assumption in
+# regalloc. This test wants to check the live interval is up-to-date after
+# register coalescing.
+#
+# To prevent the test from taking effect only in assert enabled mode, we want
+# to achieve the test goal without dumping regalloc trace. We add strong hint
+# to allocate both %t1 and %t2 to $rax register. If the %t1's live interval is
+# not shrinked properly after register coalescing, %t1 and %t2 will not be
+# both allocated to $rax because of inference, and we utilize the fact to
+# achieve the test goal. But note that the assumption only holds when we use
+# regallocbasic instead of greedy because greedy can update the live interval
+# in the process of splitting.
+#
+# CHECK-LABEL: name: foo
+# CHECK: bb.0.entry:
+# CHECK: $rax = MOV64ri32 -11
+# CHECK: bb.1:
+# CHECK: $rax = MOV64ri32 -11
+# CHECK: $rax = ADD64ri8 killed renamable $rax, 5
+# CHECK: CMP64ri8 renamable $rax
+# CHECK: RET 0, $rax
+# CHECK: bb.2:
+# CHECK: $rax = ADD64ri8 killed renamable $rax, 10
+# CHECK: bb.3:
+# CHECK: RET 0, $rax
+---
+name:            foo
+body:             |
+  bb.0.entry:
+    successors: %bb.1(0x15555555), %bb.2(0x6aaaaaab)
+
+    %t1:gr64 = MOV64ri32 -11
+    CMP64ri8 %t1, 1, implicit-def $eflags
+    JE_1 %bb.2, implicit killed $eflags
+    JMP_1 %bb.1
+
+  bb.1:
+    successors: %bb.1(0x80000000)
+
+    %t2:gr64 = COPY %t1
+    %t2:gr64 = ADD64ri8 %t2, 5, implicit-def $eflags
+    $rax = COPY %t2
+    CMP64ri8 %t2, 1, implicit-def $eflags
+    JE_1 %bb.1, implicit killed $eflags
+    RET 0, $rax
+
+  bb.2:
+    successors: %bb.3(0x80000000)
+    %t3:gr64 = COPY %t1
+    %t3:gr64 = ADD64ri8 %t3, 10, implicit-def $eflags
+
+  bb.3:
+    $rax = COPY %t3
+    RET 0, $rax
+
+...