For x86, canonicalize max
(x > y) ? x : y
=>
(x >= y) ? x : y
So for something like
(x - y) > 0 : (x - y) ? 0
It will be
(x - y) >= 0 : (x - y) ? 0
This makes is possible to test sign-bit and eliminate a comparison against
zero. e.g.
subl %esi, %edi
testl %edi, %edi
movl $0, %eax
cmovgl %edi, %eax
=>
xorl %eax, %eax
subl %esi, $edi
cmovsl %eax, %edi
rdar://10633221
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147512 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index e12343e..d33a7e0 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -13139,6 +13139,37 @@
}
}
+ // Canonicalize max and min:
+ // (x > y) ? x : y -> (x >= y) ? x : y
+ // (x < y) ? x : y -> (x <= y) ? x : y
+ // This allows use of COND_S / COND_NS (see TranslateX86CC) which eliminates
+ // the need for an extra compare
+ // against zero. e.g.
+ // (x - y) > 0 : (x - y) ? 0 -> (x - y) >= 0 : (x - y) ? 0
+ // subl %esi, %edi
+ // testl %edi, %edi
+ // movl $0, %eax
+ // cmovgl %edi, %eax
+ // =>
+ // xorl %eax, %eax
+ // subl %esi, $edi
+ // cmovsl %eax, %edi
+ if (N->getOpcode() == ISD::SELECT && Cond.getOpcode() == ISD::SETCC &&
+ DAG.isEqualTo(LHS, Cond.getOperand(0)) &&
+ DAG.isEqualTo(RHS, Cond.getOperand(1))) {
+ ISD::CondCode CC = cast<CondCodeSDNode>(Cond.getOperand(2))->get();
+ switch (CC) {
+ default: break;
+ case ISD::SETLT:
+ case ISD::SETGT: {
+ ISD::CondCode NewCC = (CC == ISD::SETLT) ? ISD::SETLE : ISD::SETGE;
+ Cond = DAG.getSetCC(Cond.getDebugLoc(), Cond.getValueType(),
+ Cond.getOperand(0), Cond.getOperand(1), NewCC);
+ return DAG.getNode(ISD::SELECT, DL, VT, Cond, LHS, RHS);
+ }
+ }
+ }
+
return SDValue();
}
diff --git a/test/CodeGen/X86/jump_sign.ll b/test/CodeGen/X86/jump_sign.ll
index 5e8e162..78dddf9 100644
--- a/test/CodeGen/X86/jump_sign.ll
+++ b/test/CodeGen/X86/jump_sign.ll
@@ -1,7 +1,9 @@
-; RUN: llc < %s -march=x86 | grep jns
+; RUN: llc < %s -march=x86 | FileCheck %s
define i32 @f(i32 %X) {
entry:
+; CHECK: f:
+; CHECK: jns
%tmp1 = add i32 %X, 1 ; <i32> [#uses=1]
%tmp = icmp slt i32 %tmp1, 0 ; <i1> [#uses=1]
br i1 %tmp, label %cond_true, label %cond_next
@@ -18,3 +20,15 @@
declare i32 @bar(...)
declare i32 @baz(...)
+
+; rdar://10633221
+define i32 @g(i32 %a, i32 %b) nounwind {
+entry:
+; CHECK: g:
+; CHECK-NOT: test
+; CHECK: cmovs
+ %sub = sub nsw i32 %a, %b
+ %cmp = icmp sgt i32 %sub, 0
+ %cond = select i1 %cmp, i32 %sub, i32 0
+ ret i32 %cond
+}