[FastISel][AArch64] Emit immediate version of icmp (subs) for null pointer check.

This is a minor change to use the immediate version when the operand is a null
value. This should get rid of an unnecessary 'mov' instruction in debug
builds and align the code more with the one generated by SelectionDAG.

This fixes rdar://problem/18785125.

llvm-svn: 220713

2 files changed, 26 insertions, 2 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64FastISel.cpp b/llvm/lib/Target/AArch64/AArch64FastISel.cpp
index 5527213c89d..01b2dee2612 100644
--- a/llvm/lib/Target/AArch64/AArch64FastISel.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FastISel.cpp
@@ -1084,7 +1084,7 @@ unsigned AArch64FastISel::emitAddSub(bool UseAdd, MVT RetVT, const Value *LHS,
   RetVT.SimpleTy = std::max(RetVT.SimpleTy, MVT::i32);
 
   // Canonicalize immediates to the RHS first.
-  if (UseAdd && isa<ConstantInt>(LHS) && !isa<ConstantInt>(RHS))
+  if (UseAdd && isa<Constant>(LHS) && !isa<Constant>(RHS))
     std::swap(LHS, RHS);
 
   // Canonicalize mul by power of 2 to the RHS.
@@ -1118,7 +1118,11 @@ unsigned AArch64FastISel::emitAddSub(bool UseAdd, MVT RetVT, const Value *LHS,
     else
       ResultReg = emitAddSub_ri(UseAdd, RetVT, LHSReg, LHSIsKill, Imm, SetFlags,
                                 WantResult);
-  }
+  } else if (const auto *C = dyn_cast<Constant>(RHS))
+    if (C->isNullValue())
+      ResultReg = emitAddSub_ri(UseAdd, RetVT, LHSReg, LHSIsKill, 0, SetFlags,
+                                WantResult);
+
   if (ResultReg)
     return ResultReg;
 
diff --git a/llvm/test/CodeGen/AArch64/arm64-fast-isel-icmp.ll b/llvm/test/CodeGen/AArch64/arm64-fast-isel-icmp.ll
index 2d60783cd1c..245c70e8905 100644
--- a/llvm/test/CodeGen/AArch64/arm64-fast-isel-icmp.ll
+++ b/llvm/test/CodeGen/AArch64/arm64-fast-isel-icmp.ll
@@ -40,6 +40,26 @@ entry:
   ret i32 %conv
 }
 
+define i32 @icmp_eq_ptr(i8* %a) {
+entry:
+; CHECK-LABEL: icmp_eq_ptr
+; CHECK:       cmp x0, #0
+; CHECK-NEXT:  cset {{.+}}, eq
+  %cmp = icmp eq i8* %a, null
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+define i32 @icmp_ne_ptr(i8* %a) {
+entry:
+; CHECK-LABEL: icmp_ne_ptr
+; CHECK:       cmp x0, #0
+; CHECK-NEXT:  cset {{.+}}, ne
+  %cmp = icmp ne i8* %a, null
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
 define i32 @icmp_ugt(i32 %a, i32 %b) nounwind ssp {
 entry:
 ; CHECK-LABEL: icmp_ugt