[SPIRVToOCL20] Remove tail from atomic_compare_exchange_strong_explicit call (#2395)

In translation from  __spirv_AtomicCompareExchange to OpenCL builtin
atomic_compare_exchange_strong_explicit, a new alloca `expected` is
created and read/written in the OpenCL builtin.
The OpenCL builtin call can't have tail marker since the marker requires
that callee doesn't access alloca from the caller.
Otherwise llvm alias analysis deduces that the alloca isn't accessed by
the call, and instcombine pass replaces the load from the alloca after
the call with the value stored to the alloca before the call.

Author: wenju-he

lib/SPIRV/SPIRVToOCL20.cpp

@@ -210,6 +210,10 @@ void SPIRVToOCL20Base::visitCallSPIRVAtomicCmpExchg(CallInst *CI) {
       &*CI->getParent()->getParent()->getEntryBlock().getFirstInsertionPt());
   PExpected->setAlignment(Align(MemTy->getScalarSizeInBits() / 8));
 
+  // Tail call implies that the callee doesn't access alloca from the caller.
+  // The newly created alloca invalidates the tail call semantics.
+  CI->setTailCall(false);
+
   // OpAtomicCompareExchangeWeak is not "weak" at all, but instead has the same
   // semantics as OpAtomicCompareExchange.
   mutateCallInst(CI, "atomic_compare_exchange_strong_explicit")

test/tail-call-atomic-cmp-exchg.ll

@@ -0,0 +1,37 @@
+; REQUIRES: pass-plugin
+; UNSUPPORTED: target={{.*windows.*}}
+
+; RUN: opt %load_spirv_lib -passes=spirv-to-ocl20 %s -S -o - | FileCheck %s
+
+; Check that tail marker is removed from atomic_compare_exchange_strong_explicit call.
+
+; CHECK: = call spir_func {{.*}}atomic_compare_exchange_strong_explicit
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+
+%"class.sycl::_V1::id" = type { %"class.sycl::_V1::detail::array" }
+%"class.sycl::_V1::detail::array" = type { [1 x i64] }
+
+define spir_kernel void @test(ptr addrspace(1) noundef align 8 %_arg_data_accessor, ptr noundef byval(%"class.sycl::_V1::id") align 8 %_arg_data_accessor4) {
+entry:
+  %0 = load i64, ptr %_arg_data_accessor4, align 8
+  %add.ptr = getelementptr inbounds ptr addrspace(4), ptr addrspace(1) %_arg_data_accessor, i64 %0
+  %arrayidx.ascast = addrspacecast ptr addrspace(1) %add.ptr to ptr addrspace(4)
+  br label %do.body
+
+do.body:
+  %call1 = tail call spir_func noundef i64 @_Z18__spirv_AtomicLoadPKmN5__spv5Scope4FlagENS1_19MemorySemanticsMask4FlagE(ptr addrspace(4) noundef %arrayidx.ascast, i32 noundef 2, i32 noundef 912)
+  %1 = inttoptr i64 %call1 to ptr addrspace(4)
+  %add.ptr.i = getelementptr inbounds i32, ptr addrspace(4) %1, i64 1
+  %2 = ptrtoint ptr addrspace(4) %add.ptr.i to i64
+  %call2 = tail call spir_func noundef i64 @_Z29__spirv_AtomicCompareExchangePmN5__spv5Scope4FlagENS0_19MemorySemanticsMask4FlagES4_mm(ptr addrspace(4) noundef %arrayidx.ascast, i32 noundef 2, i32 noundef 912, i32 noundef 912, i64 noundef %2, i64 noundef %call1)
+  %3 = icmp eq i64 %call2, %call1
+  br i1 %3, label %exit, label %do.body
+
+exit:
+  ret void
+}
+
+declare spir_func noundef i64 @_Z18__spirv_AtomicLoadPKmN5__spv5Scope4FlagENS1_19MemorySemanticsMask4FlagE(ptr addrspace(4) noundef, i32 noundef, i32 noundef)
+
+declare spir_func noundef i64 @_Z29__spirv_AtomicCompareExchangePmN5__spv5Scope4FlagENS0_19MemorySemanticsMask4FlagES4_mm(ptr addrspace(4) noundef, i32 noundef, i32 noundef, i32 noundef, i64 noundef, i64 noundef)