support branch hint for AtomicExpandImpl::expandAtomicCmpXchg (#152366)

The patch add branch hint for AtomicExpandImpl::expandAtomicCmpXchg, For
example: in PowerPC, it support branch hint as

```
loop:
    lwarx r6,0,r3   #  load and reserve
    cmpw r4,r6      #1st 2 operands equal? bne- exit  #skip if not
    bne- exit       #skip if not
    stwcx. r5,0,r3  #store new value if still res’ved bne- loop #loop if lost reservation
    bne- loop #loop if lost reservation
exit:
    mr  r4,r6       #return value from storage
```

`-`  hints not taken,
`+` hints taken,

Author: diggerlin

llvm/lib/CodeGen/AtomicExpandPass.cpp

@@ -1460,7 +1460,8 @@ bool AtomicExpandImpl::expandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
 
   // If the cmpxchg doesn't actually need any ordering when it fails, we can
   // jump straight past that fence instruction (if it exists).
-  Builder.CreateCondBr(ShouldStore, ReleasingStoreBB, NoStoreBB);
+  Builder.CreateCondBr(ShouldStore, ReleasingStoreBB, NoStoreBB,
+                       MDBuilder(F->getContext()).createLikelyBranchWeights());
 
   Builder.SetInsertPoint(ReleasingStoreBB);
   if (ShouldInsertFencesForAtomic && !UseUnconditionalReleaseBarrier)
@@ -1479,7 +1480,8 @@ bool AtomicExpandImpl::expandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
       StoreSuccess, ConstantInt::get(Type::getInt32Ty(Ctx), 0), "success");
   BasicBlock *RetryBB = HasReleasedLoadBB ? ReleasedLoadBB : StartBB;
   Builder.CreateCondBr(StoreSuccess, SuccessBB,
-                       CI->isWeak() ? FailureBB : RetryBB);
+                       CI->isWeak() ? FailureBB : RetryBB,
+                       MDBuilder(F->getContext()).createLikelyBranchWeights());
 
   Builder.SetInsertPoint(ReleasedLoadBB);
   Value *SecondLoad;
@@ -1492,7 +1494,9 @@ bool AtomicExpandImpl::expandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
 
     // If the cmpxchg doesn't actually need any ordering when it fails, we can
     // jump straight past that fence instruction (if it exists).
-    Builder.CreateCondBr(ShouldStore, TryStoreBB, NoStoreBB);
+    Builder.CreateCondBr(
+        ShouldStore, TryStoreBB, NoStoreBB,
+        MDBuilder(F->getContext()).createLikelyBranchWeights());
     // Update PHI node in TryStoreBB.
     LoadedTryStore->addIncoming(SecondLoad, ReleasedLoadBB);
   } else

llvm/test/CodeGen/AArch64/GlobalISel/arm64-atomic.ll

@@ -6002,15 +6002,17 @@ define { i8, i1 } @cmpxchg_i8(ptr %ptr, i8 %desired, i8 %new) {
 ; CHECK-NOLSE-O1-NEXT:    b.ne LBB67_4
 ; CHECK-NOLSE-O1-NEXT:  ; %bb.2: ; %cmpxchg.trystore
 ; CHECK-NOLSE-O1-NEXT:    ; in Loop: Header=BB67_1 Depth=1
-; CHECK-NOLSE-O1-NEXT:    stxrb w9, w2, [x8]
-; CHECK-NOLSE-O1-NEXT:    cbnz w9, LBB67_1
-; CHECK-NOLSE-O1-NEXT:  ; %bb.3:
-; CHECK-NOLSE-O1-NEXT:    mov w1, #1 ; =0x1
+; CHECK-NOLSE-O1-NEXT:    stxrb w10, w2, [x8]
+; CHECK-NOLSE-O1-NEXT:    mov w9, #1 ; =0x1
+; CHECK-NOLSE-O1-NEXT:    cbnz w10, LBB67_1
+; CHECK-NOLSE-O1-NEXT:  ; %bb.3: ; %cmpxchg.end
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ; kill: def $w0 killed $w0 killed $x0
 ; CHECK-NOLSE-O1-NEXT:    ret
 ; CHECK-NOLSE-O1-NEXT:  LBB67_4: ; %cmpxchg.nostore
-; CHECK-NOLSE-O1-NEXT:    mov w1, wzr
+; CHECK-NOLSE-O1-NEXT:    mov w9, wzr
 ; CHECK-NOLSE-O1-NEXT:    clrex
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ; kill: def $w0 killed $w0 killed $x0
 ; CHECK-NOLSE-O1-NEXT:    ret
 ;
@@ -6108,15 +6110,17 @@ define { i16, i1 } @cmpxchg_i16(ptr %ptr, i16 %desired, i16 %new) {
 ; CHECK-NOLSE-O1-NEXT:    b.ne LBB68_4
 ; CHECK-NOLSE-O1-NEXT:  ; %bb.2: ; %cmpxchg.trystore
 ; CHECK-NOLSE-O1-NEXT:    ; in Loop: Header=BB68_1 Depth=1
-; CHECK-NOLSE-O1-NEXT:    stxrh w9, w2, [x8]
-; CHECK-NOLSE-O1-NEXT:    cbnz w9, LBB68_1
-; CHECK-NOLSE-O1-NEXT:  ; %bb.3:
-; CHECK-NOLSE-O1-NEXT:    mov w1, #1 ; =0x1
+; CHECK-NOLSE-O1-NEXT:    stxrh w10, w2, [x8]
+; CHECK-NOLSE-O1-NEXT:    mov w9, #1 ; =0x1
+; CHECK-NOLSE-O1-NEXT:    cbnz w10, LBB68_1
+; CHECK-NOLSE-O1-NEXT:  ; %bb.3: ; %cmpxchg.end
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ; kill: def $w0 killed $w0 killed $x0
 ; CHECK-NOLSE-O1-NEXT:    ret
 ; CHECK-NOLSE-O1-NEXT:  LBB68_4: ; %cmpxchg.nostore
-; CHECK-NOLSE-O1-NEXT:    mov w1, wzr
+; CHECK-NOLSE-O1-NEXT:    mov w9, wzr
 ; CHECK-NOLSE-O1-NEXT:    clrex
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ; kill: def $w0 killed $w0 killed $x0
 ; CHECK-NOLSE-O1-NEXT:    ret
 ;
@@ -6206,22 +6210,24 @@ define { i32, i1 } @cmpxchg_i32(ptr %ptr, i32 %desired, i32 %new) {
 ; CHECK-NOLSE-O1-LABEL: cmpxchg_i32:
 ; CHECK-NOLSE-O1:       ; %bb.0:
 ; CHECK-NOLSE-O1-NEXT:    mov x8, x0
+; CHECK-NOLSE-O1-NEXT:    mov w9, #1 ; =0x1
 ; CHECK-NOLSE-O1-NEXT:  LBB69_1: ; %cmpxchg.start
 ; CHECK-NOLSE-O1-NEXT:    ; =>This Inner Loop Header: Depth=1
 ; CHECK-NOLSE-O1-NEXT:    ldxr w0, [x8]
 ; CHECK-NOLSE-O1-NEXT:    cmp w0, w1
 ; CHECK-NOLSE-O1-NEXT:    b.ne LBB69_4
 ; CHECK-NOLSE-O1-NEXT:  ; %bb.2: ; %cmpxchg.trystore
 ; CHECK-NOLSE-O1-NEXT:    ; in Loop: Header=BB69_1 Depth=1
-; CHECK-NOLSE-O1-NEXT:    stxr w9, w2, [x8]
-; CHECK-NOLSE-O1-NEXT:    cbnz w9, LBB69_1
-; CHECK-NOLSE-O1-NEXT:  ; %bb.3:
-; CHECK-NOLSE-O1-NEXT:    mov w1, #1 ; =0x1
+; CHECK-NOLSE-O1-NEXT:    stxr w10, w2, [x8]
+; CHECK-NOLSE-O1-NEXT:    cbnz w10, LBB69_1
+; CHECK-NOLSE-O1-NEXT:  ; %bb.3: ; %cmpxchg.end
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ; kill: def $w0 killed $w0 killed $x0
 ; CHECK-NOLSE-O1-NEXT:    ret
 ; CHECK-NOLSE-O1-NEXT:  LBB69_4: ; %cmpxchg.nostore
-; CHECK-NOLSE-O1-NEXT:    mov w1, wzr
+; CHECK-NOLSE-O1-NEXT:    mov w9, wzr
 ; CHECK-NOLSE-O1-NEXT:    clrex
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ; kill: def $w0 killed $w0 killed $x0
 ; CHECK-NOLSE-O1-NEXT:    ret
 ;
@@ -6306,21 +6312,23 @@ define { i64, i1 } @cmpxchg_i64(ptr %ptr, i64 %desired, i64 %new) {
 ; CHECK-NOLSE-O1-LABEL: cmpxchg_i64:
 ; CHECK-NOLSE-O1:       ; %bb.0:
 ; CHECK-NOLSE-O1-NEXT:    mov x8, x0
+; CHECK-NOLSE-O1-NEXT:    mov w9, #1 ; =0x1
 ; CHECK-NOLSE-O1-NEXT:  LBB70_1: ; %cmpxchg.start
 ; CHECK-NOLSE-O1-NEXT:    ; =>This Inner Loop Header: Depth=1
 ; CHECK-NOLSE-O1-NEXT:    ldxr x0, [x8]
 ; CHECK-NOLSE-O1-NEXT:    cmp x0, x1
 ; CHECK-NOLSE-O1-NEXT:    b.ne LBB70_4
 ; CHECK-NOLSE-O1-NEXT:  ; %bb.2: ; %cmpxchg.trystore
 ; CHECK-NOLSE-O1-NEXT:    ; in Loop: Header=BB70_1 Depth=1
-; CHECK-NOLSE-O1-NEXT:    stxr w9, x2, [x8]
-; CHECK-NOLSE-O1-NEXT:    cbnz w9, LBB70_1
-; CHECK-NOLSE-O1-NEXT:  ; %bb.3:
-; CHECK-NOLSE-O1-NEXT:    mov w1, #1 ; =0x1
+; CHECK-NOLSE-O1-NEXT:    stxr w10, x2, [x8]
+; CHECK-NOLSE-O1-NEXT:    cbnz w10, LBB70_1
+; CHECK-NOLSE-O1-NEXT:  ; %bb.3: ; %cmpxchg.end
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ret
 ; CHECK-NOLSE-O1-NEXT:  LBB70_4: ; %cmpxchg.nostore
-; CHECK-NOLSE-O1-NEXT:    mov w1, wzr
+; CHECK-NOLSE-O1-NEXT:    mov w9, wzr
 ; CHECK-NOLSE-O1-NEXT:    clrex
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ret
 ;
 ; CHECK-OUTLINE-O1-LABEL: cmpxchg_i64:
@@ -6404,21 +6412,23 @@ define { ptr, i1 } @cmpxchg_ptr(ptr %ptr, ptr %desired, ptr %new) {
 ; CHECK-NOLSE-O1-LABEL: cmpxchg_ptr:
 ; CHECK-NOLSE-O1:       ; %bb.0:
 ; CHECK-NOLSE-O1-NEXT:    mov x8, x0
+; CHECK-NOLSE-O1-NEXT:    mov w9, #1 ; =0x1
 ; CHECK-NOLSE-O1-NEXT:  LBB71_1: ; %cmpxchg.start
 ; CHECK-NOLSE-O1-NEXT:    ; =>This Inner Loop Header: Depth=1
 ; CHECK-NOLSE-O1-NEXT:    ldxr x0, [x8]
 ; CHECK-NOLSE-O1-NEXT:    cmp x0, x1
 ; CHECK-NOLSE-O1-NEXT:    b.ne LBB71_4
 ; CHECK-NOLSE-O1-NEXT:  ; %bb.2: ; %cmpxchg.trystore
 ; CHECK-NOLSE-O1-NEXT:    ; in Loop: Header=BB71_1 Depth=1
-; CHECK-NOLSE-O1-NEXT:    stxr w9, x2, [x8]
-; CHECK-NOLSE-O1-NEXT:    cbnz w9, LBB71_1
-; CHECK-NOLSE-O1-NEXT:  ; %bb.3:
-; CHECK-NOLSE-O1-NEXT:    mov w1, #1 ; =0x1
+; CHECK-NOLSE-O1-NEXT:    stxr w10, x2, [x8]
+; CHECK-NOLSE-O1-NEXT:    cbnz w10, LBB71_1
+; CHECK-NOLSE-O1-NEXT:  ; %bb.3: ; %cmpxchg.end
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ret
 ; CHECK-NOLSE-O1-NEXT:  LBB71_4: ; %cmpxchg.nostore
-; CHECK-NOLSE-O1-NEXT:    mov w1, wzr
+; CHECK-NOLSE-O1-NEXT:    mov w9, wzr
 ; CHECK-NOLSE-O1-NEXT:    clrex
+; CHECK-NOLSE-O1-NEXT:    mov w1, w9
 ; CHECK-NOLSE-O1-NEXT:    ret
 ;
 ; CHECK-OUTLINE-O1-LABEL: cmpxchg_ptr: