JIT: Fix small->float casts with AVX-512 (#112892)

Author: saucecontrol

src/coreclr/jit/codegenxarch.cpp

@@ -7287,7 +7287,7 @@ void CodeGen::genIntToFloatCast(GenTree* treeNode)
 #endif
 
     var_types dstType = treeNode->CastToType();
-    var_types srcType = op1->TypeGet();
+    var_types srcType = genActualType(op1->TypeGet());
     assert(!varTypeIsFloating(srcType) && varTypeIsFloating(dstType));
 
     // Since xarch emitter doesn't handle reporting gc-info correctly while casting away gc-ness we
@@ -7302,15 +7302,6 @@ void CodeGen::genIntToFloatCast(GenTree* treeNode)
         srcType = TYP_I_IMPL;
     }
 
-    // At this point, we should not see a srcType that is not int or long.
-    // For conversions from byte/sbyte/int16/uint16 to float/double, we would expect
-    // either the front-end or lowering phase to have generated two levels of cast.
-    // The first one is for widening smaller int type to int32 and the second one is
-    // to the float/double.
-    // On 32-bit, we expect morph to replace long to float/double casts with helper calls,
-    // so we should only see int here.
-    noway_assert(varTypeIsIntOrI(srcType));
-
     // To convert integral type to floating, the cvt[u]si2ss/sd instruction is used
     // which does a partial write to lower 4/8 bytes of xmm register keeping the other
     // upper bytes unmodified.  If "cvt[u]si2ss/sd xmmReg, r32/r64" occurs inside a loop,

src/coreclr/jit/lowerxarch.cpp

@@ -823,7 +823,6 @@ GenTree* Lowering::LowerCast(GenTree* tree)
     var_types castToType = tree->CastToType();
     var_types dstType    = castToType;
     var_types srcType    = castOp->TypeGet();
-    var_types tmpType    = TYP_UNDEF;
 
     // force the srcType to unsigned if GT_UNSIGNED flag is set
     if (tree->IsUnsigned())
@@ -837,11 +836,14 @@ GenTree* Lowering::LowerCast(GenTree* tree)
     //       Reason: must be converted to a helper call
     //   srcType = float/double,                   castToType = ulong
     //       Reason: must be converted to a helper call
+    //   srcType = float/double,                   castToType = byte/sbyte/ushort/short
+    //       Reason: must have intermediate cast to int
     //   srcType = uint                            castToType = float/double
     //       Reason: uint -> float/double = uint -> long -> float/double
     if (varTypeIsFloating(srcType))
     {
         noway_assert(!tree->gtOverflow());
+        assert(!varTypeIsSmall(dstType));
         assert(castToType != TYP_ULONG || comp->canUseEvexEncodingDebugOnly());
     }
     else if (srcType == TYP_UINT)
@@ -1164,30 +1166,6 @@ GenTree* Lowering::LowerCast(GenTree* tree)
     }
 #endif // TARGET_AMD64
 
-    // Case of src is a small type and dst is a floating point type.
-    if (varTypeIsSmall(srcType) && varTypeIsFloating(castToType))
-    {
-        // These conversions can never be overflow detecting ones.
-        noway_assert(!tree->gtOverflow());
-        tmpType = TYP_INT;
-    }
-    // case of src is a floating point type and dst is a small type.
-    else if (varTypeIsFloating(srcType) && varTypeIsSmall(castToType))
-    {
-        tmpType = TYP_INT;
-    }
-
-    if (tmpType != TYP_UNDEF)
-    {
-        GenTree* tmp = comp->gtNewCastNode(tmpType, castOp, tree->IsUnsigned(), tmpType);
-        tmp->gtFlags |= (tree->gtFlags & (GTF_OVERFLOW | GTF_EXCEPT));
-
-        tree->gtFlags &= ~GTF_UNSIGNED;
-        tree->AsOp()->gtOp1 = tmp;
-        BlockRange().InsertAfter(castOp, tmp);
-        ContainCheckCast(tmp->AsCast());
-    }
-
     // Now determine if we have operands that should be contained.
     ContainCheckCast(tree->AsCast());
     return nullptr;
@@ -8567,26 +8545,14 @@ void Lowering::ContainCheckCast(GenTreeCast* node)
 
         if (varTypeIsFloating(castToType) || varTypeIsFloating(srcType))
         {
-#ifdef DEBUG
-            // If converting to float/double, the operand must be 4 or 8 byte in size.
-            if (varTypeIsFloating(castToType))
+            if (castOp->IsCnsNonZeroFltOrDbl())
             {
-                unsigned opSize = genTypeSize(srcType);
-                assert(opSize == 4 || opSize == 8);
+                MakeSrcContained(node, castOp);
             }
-#endif // DEBUG
-
-            // U8 -> R8 conversion requires that the operand be in a register.
-            if (srcType != TYP_ULONG)
+            else
             {
-                if (castOp->IsCnsNonZeroFltOrDbl())
-                {
-                    MakeSrcContained(node, castOp);
-                }
-                else
-                {
-                    srcIsContainable = true;
-                }
+                // The ulong->floating SSE2 fallback requires the source to be in register
+                srcIsContainable = !varTypeIsSmall(srcType) && ((srcType != TYP_ULONG) || comp->canUseEvexEncoding());
             }
         }
         else if (comp->opts.OptimizationEnabled() && varTypeIsIntegral(castOp) && varTypeIsIntegral(castToType))

src/tests/JIT/Regression/JitBlue/Runtime_112871/Runtime_112871.cs

@@ -0,0 +1,23 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Generated by Fuzzlyn v2.4 on 2025-02-23 17:30:17
+// Run on X64 Windows
+// Seed: 18098778274409643257-vectort,vector128,vector256,x86aes,x86avx,x86avx2,x86avx512bw,x86avx512bwvl,x86avx512cd,x86avx512cdvl,x86avx512dq,x86avx512dqvl,x86avx512f,x86avx512fvl,x86avx512fx64,x86bmi1,x86bmi1x64,x86bmi2,x86bmi2x64,x86fma,x86lzcnt,x86lzcntx64,x86pclmulqdq,x86popcnt,x86popcntx64,x86sse,x86ssex64,x86sse2,x86sse2x64,x86sse3,x86sse41,x86sse41x64,x86sse42,x86sse42x64,x86ssse3,x86x86base
+// Reduced from 23.4 KiB to 0.4 KiB in 00:01:16
+
+using System;
+using Xunit;
+
+public class Runtime_112871
+{
+    public static short s_1;
+
+    [Fact]
+    public static void Problem()
+    {
+        ushort vr0 = default(ushort);
+        s_1 = -1;
+        Assert.True((double)0 <= (uint)s_1);
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_112871/Runtime_112871.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <Optimize>False</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>