[llvm] [X86][GlobalISel] Enable scalar versions of G_UITOFP and G_FPTOUI (PR #100079)

[Matt Arsenault via llvm-commits]

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@@ -498,6 +498,54 @@ X86LegalizerInfo::X86LegalizerInfo(const X86Subtarget &STI,
       .clampScalar(0, s32, sMaxScalar)
       .widenScalarToNextPow2(1);
 
+  // For G_UITOFP and G_FPTOUI without AVX512, we have to custom legalize types
+  // <= s32 manually. Otherwise, in custom handler there is no way to
+  // understand whether s32 is an original type and we need to promote it to
+  // s64 or s32 is obtained after widening and we shouldn't widen it to s64.
+  //
+  // For AVX512 we simply widen types as there is direct mapping from opcodes
+  // to asm instructions.
+  getActionDefinitionsBuilder(G_UITOFP)
+      .legalIf([=](const LegalityQuery &Query) {
+        return HasAVX512 && typeInSet(0, {s32, s64})(Query) &&
+               typeInSet(1, {s32, s64})(Query);
+      })
+      .lowerIf([=](const LegalityQuery &Query) {
+        // Lower conversions from s64
+        return !HasAVX512 &&
+               ((HasSSE1 && typeIs(0, s32)(Query)) ||
+                (HasSSE2 && typeIs(0, s64)(Query))) &&
+               (Is64Bit && typeIs(1, s64)(Query));
+      })
+      .customIf([=](const LegalityQuery &Query) {
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arsenm wrote:

Move customIf before lowerIf and after legalIf 

https://github.com/llvm/llvm-project/pull/100079