[llvm] [LoongArch] Override cost hooks to expose more DAG combine opportunities (PR #157824)
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Wed Sep 10 02:57:32 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-loongarch
Author: ZhaoQi (zhaoqi5)
<details>
<summary>Changes</summary>
---
Full diff: https://github.com/llvm/llvm-project/pull/157824.diff
2 Files Affected:
- (modified) llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp (+17)
- (modified) llvm/lib/Target/LoongArch/LoongArchISelLowering.h (+4)
``````````diff
diff --git a/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp b/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
index 634914d3b3fd0..f3733f04d13d3 100644
--- a/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
@@ -9094,3 +9094,20 @@ bool LoongArchTargetLowering::SimplifyDemandedBitsForTargetNode(
return TargetLowering::SimplifyDemandedBitsForTargetNode(
Op, OriginalDemandedBits, OriginalDemandedElts, Known, TLO, Depth);
}
+
+bool LoongArchTargetLowering::isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
+ unsigned Index) const {
+ if (!isOperationLegalOrCustom(ISD::EXTRACT_SUBVECTOR, ResVT))
+ return false;
+
+ // Extract a 128-bit subvector from index 0 of a 256-bit vector is free.
+ return Index == 0;
+}
+
+bool LoongArchTargetLowering::isExtractVecEltCheap(EVT VT,
+ unsigned Index) const {
+ EVT EltVT = VT.getScalarType();
+
+ // Extract a scalar FP value from index 0 of a vector is free.
+ return (EltVT == MVT::f32 || EltVT == MVT::f64) && Index == 0;
+}
diff --git a/llvm/lib/Target/LoongArch/LoongArchISelLowering.h b/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
index 9d14934a9d363..1495e98829e74 100644
--- a/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
+++ b/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
@@ -332,6 +332,10 @@ class LoongArchTargetLowering : public TargetLowering {
TargetLoweringOpt &TLO,
unsigned Depth) const override;
+ bool isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
+ unsigned Index) const override;
+ bool isExtractVecEltCheap(EVT VT, unsigned Index) const override;
+
private:
/// Target-specific function used to lower LoongArch calling conventions.
typedef bool LoongArchCCAssignFn(const DataLayout &DL, LoongArchABI::ABI ABI,
``````````
</details>
https://github.com/llvm/llvm-project/pull/157824
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