[clang] [CIR] Accept _Complex and all float formats in x86_64 callconv lowering (PR #215117)

[Andy Kaylor via cfe-commits]

================
@@ -330,15 +346,19 @@ convertABIArgInfo(const llvm::abi::ArgInfo &info, MLIRContext *ctx,
     bool coerceWidensScalar =
         origInt && coerceInt &&
         coerceInt->getSizeInBits().getFixedValue() > origInt.getWidth();
-    if (!isAggregate && !coerceIsRegisterTuple && !coerceWidensScalar)
+    // Leaving the rest alone also avoids a lossy round trip: abiTypeToCIR
+    // drops the LongDoubleType wrapper and a pointer's pointee, so comparing a
+    // scalar against its own coerce would report a difference that is not one.
+    if (!isAggregate && !comparesAgainstCoerce && !coerceIsRegisterTuple &&
+        !coerceWidensScalar)
       return ArgClassification::getDirect(nullptr);
-    // The coerce must be a type this bridge can represent.  One it cannot map
-    // (an SSE vector, or a nested type it does not handle) yields a null type.
-    // Report that as NYI instead of leaving the value as an unchanged by-value
-    // record.
     mlir::Type coerced = abiTypeToCIR(coerceAbi, ctx);
     if (!coerced)
       return std::nullopt;
+    // Coercing a value to the type it already has would add a memory round
+    // trip for nothing.
+    if (comparesAgainstCoerce && coerced == origTy)
----------------
andykaylor wrote:

Is `comparesAgainstCoerce` really necessary here? Are there cases where `coerced == origTy` that we don't want to do this?

https://github.com/llvm/llvm-project/pull/215117