[SILOptimizer] Disable SILCombiner::visitPartialApplyInst for method callees.

Disable `SILCombiner::visitPartialApplyInst` from rewriting `partial_apply` with
with `@convention(method)` callee to `thin_to_thick_function`.

This fixes SIL verification errors: `thin_to_thick_function` only supports
`@convention(thin)` operands.

Resolves SR-12548.

Author: dan-zheng

lib/SILOptimizer/SILCombiner/SILCombinerApplyVisitors.cpp

@@ -83,8 +83,10 @@ SILInstruction *SILCombiner::visitPartialApplyInst(PartialApplyInst *PAI) {
     return nullptr;
 
   // partial_apply without any substitutions or arguments is just a
-  // thin_to_thick_function.
-  if (!PAI->hasSubstitutions() && (PAI->getNumArguments() == 0)) {
+  // thin_to_thick_function. thin_to_thick_function supports only thin operands.
+  if (!PAI->hasSubstitutions() && (PAI->getNumArguments() == 0) &&
+      PAI->getSubstCalleeType()->getRepresentation() ==
+          SILFunctionTypeRepresentation::Thin) {
     if (!PAI->isOnStack())
       return Builder.createThinToThickFunction(PAI->getLoc(), PAI->getCallee(),
                                                PAI->getType());

test/AutoDiff/compiler_crashers/sr12548-siloptimizer-rewrite-partial-apply-convention-method.swift renamed to test/AutoDiff/compiler_crashers_fixed/sr12548-siloptimizer-rewrite-partial-apply-convention-method.swift

@@ -1,4 +1,4 @@
-// RUN: not %target-build-swift -O %s
+// RUN: %target-build-swift -O %s
 
 // SR-12548: SIL verification error regarding
 // `CapturePropagation::rewritePartialApply` for `partial_apply` with

test/SILOptimizer/sil_combine_apply.sil

@@ -974,3 +974,20 @@ bb0(%0: $*FakeProtocol):
   %r = tuple ()
   return %r : $()
 }
+
+// Test `partial_apply` with a `@convention(method)` callee.
+// Rewriting `partial_apply` to `thin_to_thick_function` is not okay because
+// `thin_to_thick_function` supports only `@convention(thin)` operands.
+
+sil @method : $@convention(method) (Int32) -> ()
+
+sil @test_partial_apply_method : $@convention(thin) () -> @owned @callee_owned (Int32) -> () {
+  %1 = function_ref @method : $@convention(method) (Int32) -> ()
+  %2 = partial_apply %1() : $@convention(method) (Int32) -> ()
+  return %2 : $@callee_owned (Int32) -> ()
+}
+
+// CHECK-LABEL: sil @test_partial_apply_method
+// CHECK: [[FN:%.*]] = function_ref @method
+// CHECK-NEXT: partial_apply [[FN]]()
+// CHECK-NEXT: return