[SPIR-V] Don't change switch condition type in CodeGen opts (#94959)

This change makes sure the preferred switch condition int type size
remains the same throughout CodeGen optimizations.

The change fixes running several OpenCL applications with -O2 or higher
opt levels, and fixes Basic/stream/stream_max_stmt_exceed.cpp DPC++ E2E
test with -O2.

Author: michalpaszkowski

llvm/lib/Target/SPIRV/SPIRVISelLowering.h

@@ -68,6 +68,11 @@ class SPIRVTargetLowering : public TargetLowering {
   // extra instructions required to preserve validity of SPIR-V code imposed by
   // the standard.
   void finalizeLowering(MachineFunction &MF) const override;
+
+  MVT getPreferredSwitchConditionType(LLVMContext &Context,
+                                      EVT ConditionVT) const override {
+    return ConditionVT.getSimpleVT();
+  }
 };
 } // namespace llvm
 

llvm/test/CodeGen/SPIRV/optimizations/switch-condition-type.ll

@@ -0,0 +1,18 @@
+; RUN: llc -O2 -mtriple=spirv32-unknown-unknown %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O2 -mtriple=spirv32-unknown-unknown %s -o - -filetype=obj | spirv-val %}
+
+; CHECK: %[[#INT16:]] = OpTypeInt 16 0
+; CHECK: %[[#PARAM:]] = OpFunctionParameter %[[#INT16]]
+; CHECK: OpSwitch %[[#PARAM]] %[[#]] 1 %[[#]] 2 %[[#]]
+
+define i32 @test_switch(i16 %cond) {
+entry:
+  switch i16 %cond, label %default [ i16 1, label %case_one
+                                     i16 2, label %case_two ]
+case_one:
+  ret i32 1
+case_two:
+  ret i32 2
+default:
+  ret i32 3
+}