commit 1ff6b27940bc88c6cf5234bc39bf97038b4da602
author Sanjay Patel <spatel@rotateright.com> Tue May 22 15:36:50 2018 +0000
committer Sanjay Patel <spatel@rotateright.com> Tue May 22 15:36:50 2018 +0000
tree 54acce6a27960b2bc115b649694d17685a7d4fc7
parent b6e5d4ead116a389e185cf0ee357d584933a15c4

[CodeGen] produce the LLVM canonical form of abs

We chose the 'slt' form as canonical in IR with:
rL332819
...so we should generate that form directly for efficiency.

llvm-svn: 332989

clang/lib/CodeGen/CGBuiltin.cpp

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index c6f0b30..7f1e125 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -1251,16 +1251,12 @@
   case Builtin::BI__builtin_abs:
   case Builtin::BI__builtin_labs:
   case Builtin::BI__builtin_llabs: {
+    // X < 0 ? -X : X
     Value *ArgValue = EmitScalarExpr(E->getArg(0));
-
     Value *NegOp = Builder.CreateNeg(ArgValue, "neg");
-    Value *CmpResult =
-    Builder.CreateICmpSGE(ArgValue,
-                          llvm::Constant::getNullValue(ArgValue->getType()),
-                                                            "abscond");
-    Value *Result =
-      Builder.CreateSelect(CmpResult, ArgValue, NegOp, "abs");
-
+    Constant *Zero = llvm::Constant::getNullValue(ArgValue->getType());
+    Value *CmpResult = Builder.CreateICmpSLT(ArgValue, Zero, "abscond");
+    Value *Result = Builder.CreateSelect(CmpResult, NegOp, ArgValue, "abs");
     return RValue::get(Result);
   }
   case Builtin::BI__builtin_conj:

clang/test/CodeGen/builtin-abs.c

diff --git a/clang/test/CodeGen/builtin-abs.c b/clang/test/CodeGen/builtin-abs.c
index b68d465..a6ae36c 100644
--- a/clang/test/CodeGen/builtin-abs.c
+++ b/clang/test/CodeGen/builtin-abs.c
@@ -3,8 +3,8 @@
 int absi(int x) {
 // CHECK-LABEL: @absi(
 // CHECK:   [[NEG:%.*]] = sub i32 0, [[X:%.*]]
-// CHECK:   [[CMP:%.*]] = icmp sge i32 [[X]], 0
-// CHECK:   [[SEL:%.*]] = select i1 [[CMP]], i32 [[X]], i32 [[NEG]]
+// CHECK:   [[CMP:%.*]] = icmp slt i32 [[X]], 0
+// CHECK:   [[SEL:%.*]] = select i1 [[CMP]], i32 [[NEG]], i32 [[X]]
 //
   return __builtin_abs(x);
 }
@@ -12,8 +12,8 @@
 long absl(long x) {
 // CHECK-LABEL: @absl(
 // CHECK:   [[NEG:%.*]] = sub i64 0, [[X:%.*]]
-// CHECK:   [[CMP:%.*]] = icmp sge i64 [[X]], 0
-// CHECK:   [[SEL:%.*]] = select i1 [[CMP]], i64 [[X]], i64 [[NEG]]
+// CHECK:   [[CMP:%.*]] = icmp slt i64 [[X]], 0
+// CHECK:   [[SEL:%.*]] = select i1 [[CMP]], i64 [[NEG]], i64 [[X]]
 //
   return __builtin_labs(x);
 }
@@ -21,8 +21,8 @@
 long long absll(long long x) {
 // CHECK-LABEL: @absll(
 // CHECK:   [[NEG:%.*]] = sub i64 0, [[X:%.*]]
-// CHECK:   [[CMP:%.*]] = icmp sge i64 [[X]], 0
-// CHECK:   [[SEL:%.*]] = select i1 [[CMP]], i64 [[X]], i64 [[NEG]]
+// CHECK:   [[CMP:%.*]] = icmp slt i64 [[X]], 0
+// CHECK:   [[SEL:%.*]] = select i1 [[CMP]], i64 [[NEG]], i64 [[X]]
 //
   return __builtin_llabs(x);
 }