Morph (x GT_GT.unsigned 0) into (x GT_NE 0)

IL doesn't have a cne instruction so compilers use cgt.un instead. The JIT recognizes certain patterns that involve GT_NE (e.g (x & 4) != 0) and fails if GT_GT is used instead. Transform (x GT_GT.unsigned 0) into (x GT_NE 0) and (x GT_LE.unsigned 0) into (x GT_EQ 0). The later case is rare, it sometimes occurs as a result of branch inversion.

Commit migrated from https://github.com/dotnet/coreclr/commit/45240115b06d96cb8fe32791c1cb520e9433108d

diff --git a/src/coreclr/src/jit/morph.cpp b/src/coreclr/src/jit/morph.cpp
index 17eb755..3ec6bb7 100644 (file)
--- a/src/coreclr/src/jit/morph.cpp
+++ b/src/coreclr/src/jit/morph.cpp
@@ -12213,6 +12213,23 @@ GenTreePtr Compiler::fgMorphSmpOp(GenTreePtr tree, MorphAddrContext* mac)
                         }
                     }
                 }
+                else // we have an unsigned comparison
+                {
+                    if (op2->IsIntegralConst(0))
+                    {
+                        if ((oper == GT_GT) || (oper == GT_LE))
+                        {
+                            // IL doesn't have a cne instruction so compilers use cgt.un instead. The JIT
+                            // recognizes certain patterns that involve GT_NE (e.g (x & 4) != 0) and fails
+                            // if GT_GT is used instead. Transform (x GT_GT.unsigned 0) into (x GT_NE 0)
+                            // and (x GT_LE.unsigned 0) into (x GT_EQ 0). The later case is rare, it sometimes
+                            // occurs as a result of branch inversion.
+                            oper = (oper == GT_LE) ? GT_EQ : GT_NE;
+                            tree->SetOper(oper, GenTree::PRESERVE_VN);
+                            tree->gtFlags &= ~GTF_UNSIGNED;
+                        }
+                    }
+                }
 
             COMPARE: