[llvm] c2e403c - GlobalISel: Don't fail translate on weak cmpxchg

[Matt Arsenault via llvm-commits]

Author: Matt Arsenault
Date: 2020-06-26T17:52:18-04:00
New Revision: c2e403c19d40524f868d7803b104224ca4978597

URL: https://github.com/llvm/llvm-project/commit/c2e403c19d40524f868d7803b104224ca4978597
DIFF: https://github.com/llvm/llvm-project/commit/c2e403c19d40524f868d7803b104224ca4978597.diff

LOG: GlobalISel: Don't fail translate on weak cmpxchg

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.

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index fae73873ad30..eabab3feb487 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -2023,9 +2023,6 @@ bool IRTranslator::translateAtomicCmpXchg(const User &U,
                                           MachineIRBuilder &MIRBuilder) {
   const AtomicCmpXchgInst &I = cast<AtomicCmpXchgInst>(U);
 
-  if (I.isWeak())
-    return false;
-
   auto &TLI = *MF->getSubtarget().getTargetLowering();
   auto Flags = TLI.getAtomicMemOperandFlags(I, *DL);
 

diff  --git a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
index 8e312d864798..7e806e5d0ed9 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
@@ -1968,6 +1968,32 @@ done:
   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