Revert r246232 and r246304.

This reverts isSafeToSpeculativelyExecute's use of ReadNone until we
split ReadNone into two pieces: one attribute which reasons about how
the function reasons about memory and another attribute which determines
how it may be speculated, CSE'd, trap, etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246331 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ValueTracking.cpp

@@ -3147,11 +3147,46 @@ bool llvm::isSafeToSpeculativelyExecute(const Value *V,
         LI->getPointerOperand(), LI->getAlignment(), DL, CtxI, DT, TLI);
   }
   case Instruction::Call: {
-    auto *CI = cast<CallInst>(Inst);
-    if (CI->doesNotAccessMemory() && !CI->isMustTailCall())
-      return true;
+    if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
+      switch (II->getIntrinsicID()) {
+      // 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::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:
+      case Intrinsic::uadd_with_overflow:
+      case Intrinsic::umul_with_overflow:
+      case Intrinsic::usub_with_overflow:
+        return true;
+      // Sqrt should be OK, since the llvm sqrt intrinsic isn't defined to set
+      // errno like libm sqrt would.
+      case Intrinsic::sqrt:
+      case Intrinsic::fma:
+      case Intrinsic::fmuladd:
+      case Intrinsic::fabs:
+      case Intrinsic::minnum:
+      case Intrinsic::maxnum:
+        return true;
+      // TODO: some fp intrinsics are marked as having the same error handling
+      // as libm. They're safe to speculate when they won't error.
+      // TODO: are convert_{from,to}_fp16 safe?
+      // TODO: can we list target-specific intrinsics here?
+      default: break;
+      }
+    }
     return false; // The called function could have undefined behavior or
-                  // side-effects.
+                  // side-effects, even if marked readnone nounwind.
   }
   case Instruction::VAArg:
   case Instruction::Alloca:

lib/CodeGen/Analysis.cpp

@@ -506,16 +506,18 @@ bool llvm::isInTailCallPosition(ImmutableCallSite CS, const TargetMachine &TM) {
 
   // If I will have a chain, make sure no other instruction that will have a
   // chain interposes between I and the return.
-  for (BasicBlock::const_iterator BBI = std::prev(ExitBB->end(), 2);; --BBI) {
-    if (&*BBI == I)
-      break;
-    // Debug info intrinsics do not get in the way of tail call optimization.
-    if (isa<DbgInfoIntrinsic>(BBI))
-      continue;
-    if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
-        !isSafeToSpeculativelyExecute(BBI))
-      return false;
-  }
+  if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
+      !isSafeToSpeculativelyExecute(I))
+    for (BasicBlock::const_iterator BBI = std::prev(ExitBB->end(), 2);; --BBI) {
+      if (&*BBI == I)
+        break;
+      // Debug info intrinsics do not get in the way of tail call optimization.
+      if (isa<DbgInfoIntrinsic>(BBI))
+        continue;
+      if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
+          !isSafeToSpeculativelyExecute(BBI))
+        return false;
+    }
 
   const Function *F = ExitBB->getParent();
   return returnTypeIsEligibleForTailCall(

test/Transforms/SimplifyCFG/speculate-math.ll

@@ -6,7 +6,6 @@ declare float @llvm.fmuladd.f32(float, float, float) nounwind readonly
 declare float @llvm.fabs.f32(float) nounwind readonly
 declare float @llvm.minnum.f32(float, float) nounwind readonly
 declare float @llvm.maxnum.f32(float, float) nounwind readonly
-declare float @llvm.copysign.f32(float, float) nounwind readonly
 
 ; CHECK-LABEL: @sqrt_test(
 ; CHECK: select
@@ -109,20 +108,3 @@ test_maxnum.exit:                                   ; preds = %cond.else.i, %ent
   store float %cond.i, float addrspace(1)* %out, align 4
   ret void
 }
-
-; CHECK-LABEL: @copysign_test(
-; CHECK: select
-define void @copysign_test(float addrspace(1)* noalias nocapture %out, float %a, float %b) nounwind {
-entry:
-  %cmp.i = fcmp olt float %a, 0.000000e+00
-  br i1 %cmp.i, label %test_copysign.exit, label %cond.else.i
-
-cond.else.i:                                      ; preds = %entry
-  %0 = tail call float @llvm.copysign.f32(float %a, float %b) nounwind readnone
-  br label %test_copysign.exit
-
-test_copysign.exit:                                   ; preds = %cond.else.i, %entry
-  %cond.i = phi float [ %0, %cond.else.i ], [ 0x7FF8000000000000, %entry ]
-  store float %cond.i, float addrspace(1)* %out, align 4
-  ret void
-}