[MS] Implement __iso_volatile loads/stores as builtins

[mstorsjo]

Summary

These are supposed to produce the same as normal volatile pointer loads/stores. When -volatile:ms is specified, normal volatile pointers are forced to have atomic semantics (as is the default on x86 in MSVC mode). In that case, these builtins should still produce non-atomic volatile loads/stores without acquire/release semantics, which the new test verifies.

These are only available on ARM (and on AArch64, although clang doesn't support AArch64/Windows yet).

This implements what is missing for PR30394, making it possible to compile C++ for ARM in MSVC mode with MSVC headers.

[majnemer]

IMO, this should be implemented in clang CodeGen so that we don't get extra acquire/release barriers with /volatile:ms but that might be overkill; feel free to disregard this.

[mstorsjo]

Changed to implement it as builtins, as requested. I had to put this at the bottom in EmitBuiltinExpr (which returns RValues) instead of in EmitARMBuiltinExpr (which returns Value*), since the returned Value* for stores is nullptr. A nullptr return value from EmitTargetBuiltinExpr indicates that it wasn't handled, this triggered errors about the store builtins being unsupported.

[majnemer]

lib/CodeGen/CGBuiltin.cpp

2597–2611 ↗

(On Diff #72782)

I think you could sink this into EmitARMBuiltinExpr. You don't really need or want the fancy CGF machinery here. I'd just return the result of CreateAlignedStore/CreateAlignedLoad which should handle the EmitTargetBuiltinExpr issue.

[mstorsjo]

Implemented using CreateAlignedStore and CreateAlignedLoad instead.

I'm less confident in what this actually does though - e.g. is the CreateBitCast part necessary at all? I just based this on code I found in the same file calling CreateAlignedStore. (If I comment out the CreateBitCast line, it still works just as fine, at least for the unit test - but what about actual use?)

Compared to the previous patch, the generated IR now lacks a !tbaa !3 marker at the end - is that an issue?

[majnemer]

LGTM

test/CodeGen/ms-volatile-arm.c

2 ↗

(On Diff #72988)

You don't need -fms-volatile.

[mstorsjo]

test/CodeGen/ms-volatile-arm.c

2 ↗

(On Diff #72988)

Well, originally, the point was to clarify that these volatile stores end up without atomic semantics, regardless of whether -volatile:ms has been specified. The original version of this patch (with an inline implementation in intrin.h, just using a normal volatile pointer) wouldn't pass this test, but would pass if I remove this option. But if you prefer, I can leave it out.

[majnemer]

test/CodeGen/ms-volatile-arm.c

2 ↗

(On Diff #72988)

Makes sense.

cfe/trunk/include/clang/Basic/BuiltinsARM.def

 LANGBUILTIN(__wfe, "v", "", ALL_MS_LANGUAGES)
 LANGBUILTIN(__wfi, "v", "", ALL_MS_LANGUAGES)
 LANGBUILTIN(__sev, "v", "", ALL_MS_LANGUAGES)
 LANGBUILTIN(__sevl, "v", "", ALL_MS_LANGUAGES)
 
 LANGBUILTIN(__dmb, "vUi", "nc", ALL_MS_LANGUAGES)
 LANGBUILTIN(__dsb, "vUi", "nc", ALL_MS_LANGUAGES)
 LANGBUILTIN(__isb, "vUi", "nc", ALL_MS_LANGUAGES)
+LANGBUILTIN(__iso_volatile_load8,   "ccCD*",     "n", ALL_MS_LANGUAGES)
+LANGBUILTIN(__iso_volatile_load16,  "ssCD*",     "n", ALL_MS_LANGUAGES)
+LANGBUILTIN(__iso_volatile_load32,  "iiCD*",     "n", ALL_MS_LANGUAGES)
+LANGBUILTIN(__iso_volatile_load64,  "LLiLLiCD*", "n", ALL_MS_LANGUAGES)
+LANGBUILTIN(__iso_volatile_store8,  "vcD*c",     "n", ALL_MS_LANGUAGES)
+LANGBUILTIN(__iso_volatile_store16, "vsD*s",     "n", ALL_MS_LANGUAGES)
+LANGBUILTIN(__iso_volatile_store32, "viD*i",     "n", ALL_MS_LANGUAGES)
+LANGBUILTIN(__iso_volatile_store64, "vLLiD*LLi", "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(__ldrexd, "WiWiCD*", "", ALL_MS_LANGUAGES)
 LANGBUILTIN(_MoveFromCoprocessor, "UiIUiIUiIUiIUiIUi", "", ALL_MS_LANGUAGES)
 LANGBUILTIN(_MoveFromCoprocessor2, "UiIUiIUiIUiIUiIUi", "", ALL_MS_LANGUAGES)
 LANGBUILTIN(_MoveToCoprocessor, "vUiIUiIUiIUiIUiIUi", "", ALL_MS_LANGUAGES)
 LANGBUILTIN(_MoveToCoprocessor2, "vUiIUiIUiIUiIUiIUi", "", ALL_MS_LANGUAGES)
 
 #undef BUILTIN
 #undef LANGBUILTIN

cfe/trunk/lib/CodeGen/CGBuiltin.cpp

if (BuiltinID == ARM::BI__builtin_arm_strex ||
 
     Function *F = CGM.getIntrinsic(BuiltinID == ARM::BI__builtin_arm_stlex
                                        ? Intrinsic::arm_stlex
                                        : Intrinsic::arm_strex,
                                    StoreAddr->getType());
     return Builder.CreateCall(F, {StoreVal, StoreAddr}, "strex");
   }
 
+  switch (BuiltinID) {
+  case ARM::BI__iso_volatile_load8:
+  case ARM::BI__iso_volatile_load16:
+  case ARM::BI__iso_volatile_load32:
+  case ARM::BI__iso_volatile_load64: {
+    Value *Ptr = EmitScalarExpr(E->getArg(0));
+    QualType ElTy = E->getArg(0)->getType()->getPointeeType();
+    CharUnits LoadSize = getContext().getTypeSizeInChars(ElTy);
+    llvm::Type *ITy = llvm::IntegerType::get(getLLVMContext(),
+                                             LoadSize.getQuantity() * 8);
+    Ptr = Builder.CreateBitCast(Ptr, ITy->getPointerTo());
+    llvm::LoadInst *Load =
+      Builder.CreateAlignedLoad(Ptr, LoadSize);
+    Load->setVolatile(true);
+    return Load;
+  }
+  case ARM::BI__iso_volatile_store8:
+  case ARM::BI__iso_volatile_store16:
+  case ARM::BI__iso_volatile_store32:
+  case ARM::BI__iso_volatile_store64: {
+    Value *Ptr = EmitScalarExpr(E->getArg(0));
+    Value *Value = EmitScalarExpr(E->getArg(1));
+    QualType ElTy = E->getArg(0)->getType()->getPointeeType();
+    CharUnits StoreSize = getContext().getTypeSizeInChars(ElTy);
+    llvm::Type *ITy = llvm::IntegerType::get(getLLVMContext(),
+                                             StoreSize.getQuantity() * 8);
+    Ptr = Builder.CreateBitCast(Ptr, ITy->getPointerTo());
+    llvm::StoreInst *Store =
+      Builder.CreateAlignedStore(Value, Ptr,
+                                 StoreSize);
+    Store->setVolatile(true);
+    return Store;
+  }
+  }
+
   if (BuiltinID == ARM::BI__builtin_arm_clrex) {
     Function *F = CGM.getIntrinsic(Intrinsic::arm_clrex);
     return Builder.CreateCall(F);
   }
 
   // CRC32
   Intrinsic::ID CRCIntrinsicID = Intrinsic::not_intrinsic;
   switch (BuiltinID) {

cfe/trunk/test/CodeGen/ms-volatile-arm.c

+// REQUIRES: arm-registered-target
+// RUN: %clang_cc1 -triple thumbv7-win32 -emit-llvm -fms-extensions -fms-volatile -o - < %s | FileCheck %s
+
+void test1(int volatile *p, int v) {
+  __iso_volatile_store32(p, v);
+  // CHECK-LABEL: @test1
+  // CHECK: store volatile {{.*}}, {{.*}}
+}
+int test2(const int volatile *p) {
+  return __iso_volatile_load32(p);
+  // CHECK-LABEL: @test2
+  // CHECK: load volatile {{.*}}
+}