[llvm] r301688 - [ValueTracking] Teach isSafeToSpeculativelyExecute() about the speculatable attribute

[Matt Arsenault via llvm-commits]

Author: arsenm
Date: Fri Apr 28 16:13:09 2017
New Revision: 301688

URL: http://llvm.org/viewvc/llvm-project?rev=301688&view=rev
Log:
[ValueTracking] Teach isSafeToSpeculativelyExecute() about the speculatable attribute

Patch by Tom Stellard

Added:
    llvm/trunk/test/Transforms/SimplifyCFG/speculate-call.ll
Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=301688&r1=301687&r2=301688&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Fri Apr 28 16:13:09 2017
@@ -3318,12 +3318,18 @@ bool llvm::isSafeToSpeculativelyExecute(
                                               LI->getAlignment(), DL, CtxI, DT);
   }
   case Instruction::Call: {
+    auto *CI = cast<const CallInst>(Inst);
+    const Function *Callee = CI->getCalledFunction();
+    if (Callee && Callee->isSpeculatable())
+      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...
+      // FIXME: The speculatable attribute should be added to all these
+      // intrinsics and this case statement should be removed.
       case Intrinsic::dbg_declare:
       case Intrinsic::dbg_value:
         return true;

Added: llvm/trunk/test/Transforms/SimplifyCFG/speculate-call.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/speculate-call.ll?rev=301688&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/speculate-call.ll (added)
+++ llvm/trunk/test/Transforms/SimplifyCFG/speculate-call.ll Fri Apr 28 16:13:09 2017
@@ -0,0 +1,23 @@
+; RUN: opt -S -simplifycfg < %s | FileCheck %s
+
+; CHECK-LABEL: @speculatable_attribute
+; CHECK: select
+define i32 @speculatable_attribute(i32 %a) {
+entry:
+  %c = icmp sgt i32 %a, 64
+  br i1 %c, label %end, label %if
+
+if:
+  %val = call i32 @func() #0
+  br label %end
+
+end:
+  %ret = phi i32 [%val, %if], [0, %entry]
+  ret i32 %ret
+}
+
+define i32 @func() #0 {
+  ret i32 1
+}
+attributes #0 = { nounwind readnone speculatable }
+