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authorChris Lattner <sabre@nondot.org>2005-04-12 02:19:10 +0000
committerChris Lattner <sabre@nondot.org>2005-04-12 02:19:10 +0000
commit5b95ed652fcfe578aa8af4e21318fca989164e21 (patch)
treeb1791d6b9cf62d61986587863e5b69e1b482b49c /lib
parent08b698e38db5ab5db44c0472e2a7f4f780887629 (diff)
Emit comparisons against the sign bit better. Codegen this:
bool %test1(long %X) { %A = setlt long %X, 0 ret bool %A } like this: test1: cmpl $0, 8(%esp) setl %al movzbl %al, %eax ret instead of: test1: movl 8(%esp), %ecx cmpl $0, %ecx setl %al movzbw %al, %ax cmpl $0, 4(%esp) setb %dl movzbw %dl, %dx cmpl $0, %ecx cmove %dx, %ax movzbl %al, %eax ret git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21243 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib')
-rw-r--r--lib/CodeGen/SelectionDAG/LegalizeDAG.cpp10
1 files changed, 10 insertions, 0 deletions
diff --git a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 3bd2494ceaa..7965e141a54 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -768,6 +768,16 @@ SDOperand SelectionDAGLegalize::LegalizeOp(SDOperand Op) {
DAG.getConstant(0, Tmp1.getValueType()));
break;
default:
+ // If this is a comparison of the sign bit, just look at the top part.
+ // X > -1, x < 0
+ if (ConstantSDNode *CST = dyn_cast<ConstantSDNode>(Node->getOperand(1)))
+ if ((cast<SetCCSDNode>(Node)->getCondition() == ISD::SETLT &&
+ CST->getValue() == 0) || // X < 0
+ (cast<SetCCSDNode>(Node)->getCondition() == ISD::SETGT &&
+ (CST->isAllOnesValue()))) // X > -1
+ return DAG.getSetCC(cast<SetCCSDNode>(Node)->getCondition(),
+ Node->getValueType(0), LHSHi, RHSHi);
+
// FIXME: This generated code sucks.
ISD::CondCode LowCC;
switch (cast<SetCCSDNode>(Node)->getCondition()) {