[PATCH] D81733: GlobalISel: Don't fail translate on weak cmpxchg

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added reviewers: dsanders, t.p.northover, aemerson, paquette, reames, aditya_nandakumar.
Herald added subscribers: jfb, hiraditya, rovka, wdng.
Herald added a project: LLVM.

The translation of cmpxchg added by
9481399c0fd2c198c81b92636c0dcff7d4c41df2 specifically skipped weak
cmpxchg due to not understanding the meaning. Weak cmpxchg was added
in 420a216817def01816186910a2e35885c9201951. As explained in the
commit message, the weak mode is implicit in how
ATOMIC_CMP_SWAP_WITH_SUCCESS is lowered. If it's expanded to a regular
ATOMIC_CMP_SWAP, it's replaced with a strong cmpxchg.

      

This handling seems weird to me, but this was already following the
DAG behavior. I would expect the strong IR instruction to not have the
boolean output. Failing that, I might expect the IRTranslator to emit
ATOMIC_CMP_SWAP and a constant for the boolean.


https://reviews.llvm.org/D81733

Files:
  llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll


Index: llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
+++ llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
@@ -1968,6 +1968,32 @@
   ret i32 %value_loaded
 }
 
+; Try one cmpxchg
+define i32 @test_weak_atomic_cmpxchg_1(i32* %addr) {
+; CHECK-LABEL: name: test_weak_atomic_cmpxchg_1
+; CHECK:       bb.1.entry:
+; CHECK-NEXT:  successors: %bb.{{[^)]+}}
+; CHECK-NEXT:  liveins: $x0
+; CHECK:         [[ADDR:%[0-9]+]]:_(p0) = COPY $x0
+; CHECK-NEXT:    [[OLDVAL:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+; CHECK-NEXT:    [[NEWVAL:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+; CHECK:       bb.2.repeat:
+; CHECK-NEXT:    successors: %bb.3({{[^)]+}}), %bb.2({{[^)]+}})
+; CHECK:         [[OLDVALRES:%[0-9]+]]:_(s32), [[SUCCESS:%[0-9]+]]:_(s1) = G_ATOMIC_CMPXCHG_WITH_SUCCESS [[ADDR]](p0), [[OLDVAL]], [[NEWVAL]] :: (load store monotonic monotonic 4 on %ir.addr)
+; CHECK-NEXT:    G_BRCOND [[SUCCESS]](s1), %bb.3
+; CHECK-NEXT:    G_BR %bb.2
+; CHECK:       bb.3.done:
+entry:
+  br label %repeat
+repeat:
+  %val_success = cmpxchg weak i32* %addr, i32 0, i32 1 monotonic monotonic
+  %value_loaded = extractvalue { i32, i1 } %val_success, 0
+  %success = extractvalue { i32, i1 } %val_success, 1
+  br i1 %success, label %done, label %repeat
+done:
+  ret i32 %value_loaded
+}
+
 ; Try one cmpxchg with a small type and high atomic ordering.
 define i16 @test_atomic_cmpxchg_2(i16* %addr) {
 ; CHECK-LABEL: name: test_atomic_cmpxchg_2
Index: llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -2023,9 +2023,6 @@
                                           MachineIRBuilder &MIRBuilder) {
   const AtomicCmpXchgInst &I = cast<AtomicCmpXchgInst>(U);
 
-  if (I.isWeak())
-    return false;
-
   auto &TLI = *MF->getSubtarget().getTargetLowering();
   auto Flags = TLI.getAtomicMemOperandFlags(I, *DL);
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D81733.270374.patch
Type: text/x-patch
Size: 2101 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200612/fa292cb7/attachment.bin>