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();
}