[𝘀𝗽𝗿] changes to main this commit is based on

Created using spr 1.3.4

[skip ci]

Author: vitalybuka

llvm/docs/LangRef.rst

@@ -27553,7 +27553,7 @@ in example below:
 .. code-block:: text
 
     %cond = call i1 @llvm.experimental.widenable.condition()
-    br i1 %cond, label %solution_1, label %solution_2
+    br i1 %cond, label %fast_path, label %slow_path
 
   label %fast_path:
     ; Apply memory-consuming but fast solution for a task.
@@ -27639,6 +27639,54 @@ constant `true`. However it is always correct to replace
 it with any other `i1` value. Any pass can
 freely do it if it can benefit from non-default lowering.
 
+'``llvm.experimental.hot``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare i1 @llvm.experimental.hot()
+
+Overview:
+"""""""""
+
+This intrinsic returns true iff it's known that containing basic block is hot in
+profile.
+
+When used with profile based optimization allows to change program behaviour
+deppending on the code hotness.
+
+Arguments:
+""""""""""
+
+None.
+
+Semantics:
+""""""""""
+
+The intrinsic ``@llvm.experimental.hot()`` returns either `true` or `false`,
+deppending on profile used. Expresion is evaluated as `true` iff profile and
+summary are availible and profile counter for the block reach hotness threshold.
+For each evaluation of a call to this intrinsic, the program must be valid and
+correct both if it returns `true` and if it returns `false`.
+
+When used in a branch condition, it allows us to choose between
+two alternative correct solutions for the same problem, like
+in example below:
+
+.. code-block:: text
+
+    %cond = call i1 @llvm.experimental.hot()
+    br i1 %cond, label %fast_path, label %slow_path
+
+  label %fast_path:
+    ; Omit diagnostics.
+
+  label %slow_path:
+    ; Additional diagnostics.
+
 
 '``llvm.load.relative``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

llvm/include/llvm/IR/Intrinsics.td

@@ -1722,6 +1722,11 @@ def int_debugtrap : Intrinsic<[]>,
 def int_ubsantrap : Intrinsic<[], [llvm_i8_ty],
                               [IntrNoReturn, IntrCold, ImmArg<ArgIndex<0>>]>;
 
+// Return true if profile counter for containing block is hot.
+def int_experimental_hot : Intrinsic<[llvm_i1_ty], [],
+                                      [IntrInaccessibleMemOnly, IntrWriteMem,
+                                       IntrWillReturn, NoUndef<RetIndex>]>;
+
 // Support for dynamic deoptimization (or de-specialization)
 def int_experimental_deoptimize : Intrinsic<[llvm_any_ty], [llvm_vararg_ty],
                                             [Throws]>;

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -7276,6 +7276,12 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
     setValue(&I, getValue(I.getArgOperand(0)));
     return;
 
+  case Intrinsic::experimental_hot:
+    // Default lowering to false. It's intended to be lowered as soon as profile
+    // is avalible to unblock other optimizations.
+    setValue(&I, DAG.getConstant(0, sdl, MVT::i1));
+    return;
+
   case Intrinsic::ubsantrap:
   case Intrinsic::debugtrap:
   case Intrinsic::trap: {

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -2827,6 +2827,14 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         }))
       return nullptr;
     break;
+  case Intrinsic::experimental_hot: {
+    // The intrinsic declaration includes sideeffects to avoid it moved. This
+    // prevents removing even if the intrinsic is unused. We should remove
+    // unused ones to enabled other optimizations.
+    if (CI.use_empty())
+      return eraseInstFromFunction(CI);
+    break;
+  }
   case Intrinsic::assume: {
     Value *IIOperand = II->getArgOperand(0);
     SmallVector<OperandBundleDef, 4> OpBundles;

llvm/test/CodeGen/Generic/builtin-hot.ll

@@ -0,0 +1,19 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc -o - %s | FileCheck %s
+
+; REQUIRES: aarch64-registered-target
+
+target triple = "aarch64-linux"
+
+define i1 @test()  {
+; CHECK-LABEL: test:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mov w0, wzr
+; CHECK-NEXT:    ret
+entry:
+  %hot = call i1 @llvm.experimental.hot()
+  ret i1 %hot
+}
+
+declare i1 @llvm.expect.hot() nounwind
+

llvm/test/Transforms/InstCombine/builtin-hot.ll

@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i1 @test()  {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[HOT:%.*]] = call i1 @llvm.experimental.hot()
+; CHECK-NEXT:    ret i1 [[HOT]]
+;
+entry:
+  %hot = call i1 @llvm.experimental.hot()
+  ret i1 %hot
+}
+
+define void @test_void()  {
+; CHECK-LABEL: @test_void(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %hot = call i1 @llvm.experimental.hot()
+  ret void
+}
+
+declare i1 @llvm.expect.hot() nounwind