Fix ValueTracking to conclude that debug intrinsics are safe to
speculate. Without this, loop rotate (among many other places) would
suddenly stop working in the presence of debug info. I found this
looking at loop rotate, and have augmented its tests with a reduction
out of a very hot loop in yacr2 where failing to do this rotation costs
sometimes more than 10% in runtime performance, perturbing numerous
downstream optimizations.
This should have no impact on performance without debug info, but the
change in performance when debug info is enabled can be extreme. As
a consequence (and this how I got to this yak) any profiling of
performance problems should be treated with deep suspicion -- they may
have been wildly innacurate of debug info was enabled for profiling. =/
Just a heads up.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154263 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index c6b53a9..a430f62 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -1854,6 +1854,14 @@
case Instruction::Call: {
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: