Add __builtin_assume and __builtin_assume_aligned using @llvm.assume.

This makes use of the recently-added @llvm.assume intrinsic to implement a
__builtin_assume(bool) intrinsic (to provide additional information to the
optimizer). This hooks up __assume in MS-compatibility mode to mirror
__builtin_assume (the semantics have been intentionally kept compatible), and
implements GCC's __builtin_assume_aligned as assume((p - o) & mask == 0). LLVM
now contains special logic to deal with assumptions of this form.

llvm-svn: 217349

1 files changed, 28 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index fc9e60d1329..426ec7496c4 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -711,6 +711,34 @@ EmitComplexPrePostIncDec(const UnaryOperator *E, LValue LV,
   return isPre ? IncVal : InVal;
 }
 
+void CodeGenFunction::EmitAlignmentAssumption(llvm::Value *PtrValue,
+                                              unsigned Alignment,
+                                              llvm::Value *OffsetValue) {
+  llvm::Value *PtrIntValue =
+    Builder.CreatePtrToInt(PtrValue, IntPtrTy, "ptrint");
+
+  llvm::Value *Mask = llvm::ConstantInt::get(IntPtrTy,
+    Alignment > 0 ? Alignment - 1 : 0);
+  if (OffsetValue) {
+    bool IsOffsetZero = false;
+    if (llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(OffsetValue))
+      IsOffsetZero = CI->isZero();
+
+    if (!IsOffsetZero) {
+      if (OffsetValue->getType() != IntPtrTy)
+        OffsetValue = Builder.CreateIntCast(OffsetValue, IntPtrTy,
+                        /*isSigned*/true, "offsetcast");
+      PtrIntValue = Builder.CreateSub(PtrIntValue, OffsetValue, "offsetptr");
+    }
+  }
+
+  llvm::Value *Zero = llvm::ConstantInt::get(IntPtrTy, 0);
+  llvm::Value *MaskedPtr = Builder.CreateAnd(PtrIntValue, Mask, "maskedptr");
+  llvm::Value *InvCond = Builder.CreateICmpEQ(MaskedPtr, Zero, "maskcond");
+
+  llvm::Value *FnAssume = CGM.getIntrinsic(llvm::Intrinsic::assume);
+  Builder.CreateCall(FnAssume, InvCond);
+}
 
 //===----------------------------------------------------------------------===//
 //                         LValue Expression Emission