[PATCH] D22685: Disable shrinking of SNaN constants on SystemZ

[Elliot Colp via llvm-commits]

colpell updated this revision to Diff 65507.
colpell added a comment.

Re-add test case that went missing.


https://reviews.llvm.org/D22685

Files:
  include/llvm/Target/TargetLowering.h
  lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
  lib/Target/SystemZ/SystemZISelLowering.h
  test/CodeGen/SystemZ/fp-const-10.ll

Index: test/CodeGen/SystemZ/fp-const-10.ll
===================================================================
--- test/CodeGen/SystemZ/fp-const-10.ll
+++ test/CodeGen/SystemZ/fp-const-10.ll
@@ -0,0 +1,15 @@
+; Test loads of SNaN.
+;
+; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
+
+; Test that we don't do an FP extending load, as this would result in a
+; converstion to QNaN.
+define double @f1() {
+; CHECK-LABEL: .LCPI0_0
+; CHECK:      .quad   9219994337134247936
+; CHECK-LABEL: f1:
+; CHECK:      larl    %r1, .LCPI0_0
+; CHECK-NOT:  ldeb    %f0, 0(%r1)
+; CHECK:      ld      %f0, 0(%r1)
+  ret double 0x7FF4000000000000
+}
Index: lib/Target/SystemZ/SystemZISelLowering.h
===================================================================
--- lib/Target/SystemZ/SystemZISelLowering.h
+++ lib/Target/SystemZ/SystemZISelLowering.h
@@ -486,6 +486,10 @@
     return true;
   }
 
+  bool ShouldShrinkSNaNConstant() const override {
+    return false;
+  }
+
 private:
   const SystemZSubtarget &Subtarget;
 
Index: lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -259,19 +259,23 @@
                            (VT == MVT::f64) ? MVT::i64 : MVT::i32);
   }
 
+  APFloat APF = CFP->getValueAPF();
   EVT OrigVT = VT;
   EVT SVT = VT;
-  while (SVT != MVT::f32 && SVT != MVT::f16) {
-    SVT = (MVT::SimpleValueType)(SVT.getSimpleVT().SimpleTy - 1);
-    if (ConstantFPSDNode::isValueValidForType(SVT, CFP->getValueAPF()) &&
-        // Only do this if the target has a native EXTLOAD instruction from
-        // smaller type.
-        TLI.isLoadExtLegal(ISD::EXTLOAD, OrigVT, SVT) &&
-        TLI.ShouldShrinkFPConstant(OrigVT)) {
-      Type *SType = SVT.getTypeForEVT(*DAG.getContext());
-      LLVMC = cast<ConstantFP>(ConstantExpr::getFPTrunc(LLVMC, SType));
-      VT = SVT;
-      Extend = true;
+
+  if (TLI.ShouldShrinkSNaNConstant() || !APF.isSignaling()) {
+    while (SVT != MVT::f32 && SVT != MVT::f16) {
+      SVT = (MVT::SimpleValueType)(SVT.getSimpleVT().SimpleTy - 1);
+      if (ConstantFPSDNode::isValueValidForType(SVT, APF) &&
+          // Only do this if the target has a native EXTLOAD instruction from
+          // smaller type.
+          TLI.isLoadExtLegal(ISD::EXTLOAD, OrigVT, SVT) &&
+          TLI.ShouldShrinkFPConstant(OrigVT)) {
+        Type *SType = SVT.getTypeForEVT(*DAG.getContext());
+        LLVMC = cast<ConstantFP>(ConstantExpr::getFPTrunc(LLVMC, SType));
+        VT = SVT;
+        Extend = true;
+      }
     }
   }
 
Index: include/llvm/Target/TargetLowering.h
===================================================================
--- include/llvm/Target/TargetLowering.h
+++ include/llvm/Target/TargetLowering.h
@@ -887,6 +887,12 @@
   /// reduce runtime.
   virtual bool ShouldShrinkFPConstant(EVT) const { return true; }
 
+  /// If true (and ShouldShrinkFPConstant is also true), then instruction
+  /// selection should shrink SNaN constants. This is needeed for architectures
+  /// (e.g. SystemZ) in which FP extending loads of a SNaN result in a QNaN
+  /// instead.
+  virtual bool ShouldShrinkSNaNConstant() const { return true; }
+
   // Return true if it is profitable to reduce the given load node to a smaller
   // type.
   //


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