[ValueTracking] Teach isSafeToSpeculativelyExecute() about the speculatable attribute

Patch by Tom Stellard

llvm-svn: 301688

2 files changed, 29 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 113e957438d..339668347b4 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3318,12 +3318,18 @@ bool llvm::isSafeToSpeculativelyExecute(const Value *V,
                                               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;
diff --git a/llvm/test/Transforms/SimplifyCFG/speculate-call.ll b/llvm/test/Transforms/SimplifyCFG/speculate-call.ll
new file mode 100644
index 00000000000..6e9398b6203
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/speculate-call.ll
@@ -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 }
+