Intrinsic::Bitreverse is safe to speculate

[trentxintong]

Summary

Intrinsic::Bitreverse is safe to speculate

[hfinkel]

LGTM

llvm/trunk/lib/Analysis/ValueTracking.cpp

if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
       // These synthetic intrinsics have no side-effects and just mark
       // information about their operands.
       // FIXME: There are other no-op synthetic instructions that potentially
       // should be considered at least *safe* to speculate...
       case Intrinsic::dbg_declare:
       case Intrinsic::dbg_value:
         return true;
 
+      case Intrinsic::bitreverse:
       case Intrinsic::bswap:
       case Intrinsic::ctlz:
       case Intrinsic::ctpop:
       case Intrinsic::cttz:
       case Intrinsic::objectsize:
       case Intrinsic::sadd_with_overflow:
       case Intrinsic::smul_with_overflow:
       case Intrinsic::ssub_with_overflow:

llvm/trunk/test/Transforms/LICM/hoisting.ll

 ; RUN: opt < %s -licm -S | FileCheck %s
 ; RUN: opt -lcssa %s | opt -aa-pipeline=basic-aa -passes='require<aa>,require<targetir>,require<scalar-evolution>,loop(licm)' -S | FileCheck %s
 
 @X = global i32 0   ; <i32*> [#uses=1]
 
 declare void @foo()
 
+declare i32 @llvm.bitreverse.i32(i32)
+
 ; This testcase tests for a problem where LICM hoists 
 ; potentially trapping instructions when they are not guaranteed to execute.
 define i32 @test1(i1 %c) {
 ; CHECK-LABEL: @test1(
   %A = load i32, i32* @X    ; <i32> [#uses=2]
   br label %Loop
 Loop:   ; preds = %LoopTail, %0
   call void @foo( )

 then:                                             ; preds = %tailrecurse
   call void @foo()
   %cmp2 = add i32 %i.tr, 1
   br label %tailrecurse
 
 ifend:                                            ; preds = %tailrecurse
   ret { i32*, i32 } %d
 }
+
+; CHECK: define i32 @hoist_bitreverse(i32)
+; CHECK: bitreverse
+; CHECK: br label %header
+define i32 @hoist_bitreverse(i32)  {
+  br label %header
+
+header:
+  %sum = phi i32 [ 0, %1 ], [ %5, %latch ]
+  %2 = phi i32 [ 0, %1 ], [ %6, %latch ]
+  %3 = icmp slt i32 %2, 1024
+  br i1 %3, label %body, label %return
+
+body:
+  %4 = call i32 @llvm.bitreverse.i32(i32 %0)
+  %5 = add i32 %sum, %4
+  br label %latch
+
+latch:
+  %6 = add nsw i32 %2, 1
+  br label %header
+
+return:
+  ret i32 %sum
+}