Add a target lowering hook to control whether it's worthwhile to compress fp constant.
For x86, if sse2 is available, it's not a good idea since cvtss2sd is slower than a movsd load and it prevents load folding. On x87, it's important to shrink fp constant since fldt is very expensive.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47931 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index a3d24cc..ac573c4 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -467,6 +467,11 @@
assert(0 && "Unsupported extended type!");
}
+ /// ShouldShrinkFPConstant - If true, then instruction selection should
+ /// seek to shrink the FP constant of the specified type to a smaller type
+ /// in order to save space and / or reduce runtime.
+ virtual bool ShouldShrinkFPConstant(MVT::ValueType VT) const { return true; }
+
/// hasTargetDAGCombine - If true, the target has custom DAG combine
/// transformations that it can perform for the specified node.
bool hasTargetDAGCombine(ISD::NodeType NT) const {
diff --git a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index c1bf218..24dd2fd 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -504,7 +504,8 @@
if (CFP->isValueValidForType(SVT, CFP->getValueAPF()) &&
// Only do this if the target has a native EXTLOAD instruction from
// smaller type.
- TLI.isLoadXLegal(ISD::EXTLOAD, SVT)) {
+ TLI.isLoadXLegal(ISD::EXTLOAD, SVT) &&
+ TLI.ShouldShrinkFPConstant(VT)) {
const Type *SType = MVT::getTypeForValueType(SVT);
LLVMC = cast<ConstantFP>(ConstantExpr::getFPTrunc(LLVMC, SType));
VT = SVT;
diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h
index d9593a4..e0ddf63 100644
--- a/lib/Target/X86/X86ISelLowering.h
+++ b/lib/Target/X86/X86ISelLowering.h
@@ -434,6 +434,16 @@
virtual bool isVectorClearMaskLegal(std::vector<SDOperand> &BVOps,
MVT::ValueType EVT,
SelectionDAG &DAG) const;
+
+ /// ShouldShrinkFPConstant - If true, then instruction selection should
+ /// seek to shrink the FP constant of the specified type to a smaller type
+ /// in order to save space and / or reduce runtime.
+ virtual bool ShouldShrinkFPConstant(MVT::ValueType VT) const {
+ // Don't shrink FP constpool if SSE2 is available since cvtss2sd is more
+ // expensive than a straight movsd. On the other hand, it's important to
+ // shrink long double fp constant since fldt is very slow.
+ return !X86ScalarSSEf64 || VT == MVT::f80;
+ }
/// IsEligibleForTailCallOptimization - Check whether the call is eligible
/// for tail call optimization. Target which want to do tail call
diff --git a/test/CodeGen/X86/shrink-fp-const1.ll b/test/CodeGen/X86/shrink-fp-const1.ll
new file mode 100644
index 0000000..966e69e
--- /dev/null
+++ b/test/CodeGen/X86/shrink-fp-const1.ll
@@ -0,0 +1,7 @@
+; RUN: llvm-as < %s | llc -march=x86-64 -mattr=+sse2 | not grep cvtss2sd
+; PR1264
+
+define double @foo(double %x) {
+ %y = mul double %x, 5.000000e-01
+ ret double %y
+}