[llvm] [X86] Do not combine LRINT and TRUNC (PR #125848)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Phoebe Wang (phoebewang)

<details>
<summary>Changes</summary>

Per to discussions in #<!-- -->125324, most participants are opposed to this optimization. So remove the combination to address the concerns.

Fixes #<!-- -->125324

---
Full diff: https://github.com/llvm/llvm-project/pull/125848.diff


2 Files Affected:

- (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (-5) 
- (modified) llvm/test/CodeGen/X86/lrint-conv-i64.ll (+18) 


``````````diff
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 6cf6061deba702..5686d8bcbe85cd 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -53906,11 +53906,6 @@ static SDValue combineTruncate(SDNode *N, SelectionDAG &DAG,
       return DAG.getNode(X86ISD::MMX_MOVD2W, DL, MVT::i32, BCSrc);
   }
 
-  // Try to combine (trunc (vNi64 (lrint x))) to (vNi32 (lrint x)).
-  if (Src.getOpcode() == ISD::LRINT && VT.getScalarType() == MVT::i32 &&
-      Src.hasOneUse())
-    return DAG.getNode(ISD::LRINT, DL, VT, Src.getOperand(0));
-
   return SDValue();
 }
 
diff --git a/llvm/test/CodeGen/X86/lrint-conv-i64.ll b/llvm/test/CodeGen/X86/lrint-conv-i64.ll
index 01b0af2f807f20..38fa09085e1898 100644
--- a/llvm/test/CodeGen/X86/lrint-conv-i64.ll
+++ b/llvm/test/CodeGen/X86/lrint-conv-i64.ll
@@ -45,6 +45,24 @@ entry:
   ret i64 %0
 }
 
+define i32 @PR125324(float %x) {
+; SSE-LABEL: PR125324:
+; SSE:       # %bb.0: # %entry
+; SSE-NEXT:    cvtss2si %xmm0, %rax
+; SSE-NEXT:    # kill: def $eax killed $eax killed $rax
+; SSE-NEXT:    retq
+;
+; AVX-LABEL: PR125324:
+; AVX:       # %bb.0: # %entry
+; AVX-NEXT:    vcvtss2si %xmm0, %rax
+; AVX-NEXT:    # kill: def $eax killed $eax killed $rax
+; AVX-NEXT:    retq
+entry:
+  %0 = tail call i64 @llvm.lrint.i64.f32(float %x)
+  %1 = trunc i64 %0 to i32
+  ret i32 %1
+}
+
 declare i64 @llvm.lrint.i64.f32(float) nounwind readnone
 declare i64 @llvm.lrint.i64.f64(double) nounwind readnone
 declare i64 @llvm.lrint.i64.f80(x86_fp80) nounwind readnone

``````````

</details>


https://github.com/llvm/llvm-project/pull/125848