[llvm] [NVPTX] Implement isTruncateFree and isZExtFree for i32/i64 Optimizations (PR #114658)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-nvptx

Author: None (Quark-69)

<details>
<summary>Changes</summary>

Solves #<!-- -->114339 

Implemented the isTruncateFree and isZExtFree virtual functions in the NVPTXTargetLowering class. This implementation optimizes truncation from i64 to i32 and zero-extension from i32 to i64, recognizing that these operations can be considered free in the NVPTX architecture.

Details:
- The isTruncateFree function returns true for truncation from i64 to i32.
- The isZExtFree function is implemented to return `true` for zero-extension from i32 to i64.
- These changes improve the efficiency of code generation by leveraging hardware capabilities.

Testing:
- Added lit tests to validate the functionality of these optimizations.

---
Full diff: https://github.com/llvm/llvm-project/pull/114658.diff


3 Files Affected:

- (modified) llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp (+23) 
- (modified) llvm/lib/Target/NVPTX/NVPTXISelLowering.h (+4) 
- (added) llvm/test/CodeGen/NVPTX/truncate_zext.ll (+17) 


``````````diff
diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
index d3bf0ecfe2cc92..b5fc975d71dfa8 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
@@ -3340,6 +3340,29 @@ bool NVPTXTargetLowering::splitValueIntoRegisterParts(
   return false;
 }
 
+bool llvm::NVPTXTargetLowering::isTruncateFree(EVT FromVT, EVT ToVT) const {
+
+  if (!FromVT.isSimple() || !ToVT.isSimple()) {
+    return false;
+  }
+
+  return (FromVT.getSimpleVT() == MVT::i64 && ToVT.getSimpleVT() == MVT::i32);
+}
+
+bool llvm::NVPTXTargetLowering::isZExtFree(EVT FromVT, EVT ToVT) const {
+  if (!FromVT.isSimple() || !ToVT.isSimple()) {
+    return false;
+  }
+  return (FromVT.getSimpleVT() == MVT::i32 && ToVT.getSimpleVT() == MVT::i64);
+}
+
+bool llvm::NVPTXTargetLowering::isZExtFree(Type *SrcTy, Type *DstTy) const {
+  if (!SrcTy->isIntegerTy() || !DstTy->isIntegerTy())
+    return false;
+  return SrcTy->getPrimitiveSizeInBits() == 32 &&
+         DstTy->getPrimitiveSizeInBits() == 64;
+}
+
 // This creates target external symbol for a function parameter.
 // Name of the symbol is composed from its index and the function name.
 // Negative index corresponds to special parameter (unsized array) used for
diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.h b/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
index c8b589ae39413e..fa73938a35a168 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
@@ -616,6 +616,10 @@ class NVPTXTargetLowering : public TargetLowering {
     return true;
   }
 
+  bool isTruncateFree(EVT FromVT, EVT ToVT) const override;
+  bool isZExtFree(EVT FromVT, EVT ToVT) const override;
+  bool isZExtFree(Type *SrcTy, Type *DstTy) const override;
+
 private:
   const NVPTXSubtarget &STI; // cache the subtarget here
   SDValue getParamSymbol(SelectionDAG &DAG, int idx, EVT) const;
diff --git a/llvm/test/CodeGen/NVPTX/truncate_zext.ll b/llvm/test/CodeGen/NVPTX/truncate_zext.ll
new file mode 100644
index 00000000000000..decc02c5840491
--- /dev/null
+++ b/llvm/test/CodeGen/NVPTX/truncate_zext.ll
@@ -0,0 +1,17 @@
+; RUN: llc -march=nvptx64 < %s | FileCheck %s
+
+; Test for truncation from i64 to i32
+define i32 @test_trunc_i64_to_i32(i64 %val) {
+  ; CHECK-LABEL: test_trunc_i64_to_i32
+  ; CHECK: trunc
+  %trunc = trunc i64 %val to i32
+  ret i32 %trunc
+}
+
+; Test for zero-extension from i32 to i64
+define i64 @test_zext_i32_to_i64(i32 %val) {
+  ; CHECK-LABEL: test_zext_i32_to_i64
+  ; CHECK: zext
+  %zext = zext i32 %val to i64
+  ret i64 %zext
+}
\ No newline at end of file

``````````

</details>


https://github.com/llvm/llvm-project/pull/114658