[AddDiscriminators] Assign discriminators to MemIntrinsic calls.

Before this patch, pass AddDiscriminators always avoided to assign
discriminators to intrinsic calls. This was done mainly for two reasons:
 1) We wanted to minimize the number of based discriminators used.
 2) We wanted to avoid non-deterministic discriminator assignment for
    different debug levels.

Unfortunately, that approach was problematic for MemIntrinsic calls.
MemIntrinsic calls can be split by SROA into loads and stores, and each new
load/store instruction would obtain the debug location from the original
intrinsic call.
If we don't assign a discriminator to MemIntrinsic calls, then we cannot
correctly set the discriminator for the newly created loads and stores.
This may have a negative impact on the basic block weight computation
performed by the SampleLoader.

This patch fixes the issue by letting MemIntrinsic calls have a discriminator.

Differential Revision: https://reviews.llvm.org/D31900

llvm-svn: 299972

1 files changed, 15 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
index 0d8ee844d3f..4c9746b8c69 100644
--- a/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
+++ b/llvm/lib/Transforms/Utils/AddDiscriminators.cpp
@@ -102,6 +102,10 @@ FunctionPass *llvm::createAddDiscriminatorsPass() {
   return new AddDiscriminatorsLegacyPass();
 }
 
+static bool shouldHaveDiscriminator(const Instruction *I) {
+  return !isa<IntrinsicInst>(I) || isa<MemIntrinsic>(I);
+}
+
 /// \brief Assign DWARF discriminators.
 ///
 /// To assign discriminators, we examine the boundaries of every
@@ -176,7 +180,13 @@ static bool addDiscriminators(Function &F) {
   // discriminator for this instruction.
   for (BasicBlock &B : F) {
     for (auto &I : B.getInstList()) {
-      if (isa<IntrinsicInst>(&I))
+      // Not all intrinsic calls should have a discriminator.
+      // We want to avoid a non-deterministic assignment of discriminators at
+      // different debug levels. We still allow discriminators on memory
+      // intrinsic calls because those can be early expanded by SROA into
+      // pairs of loads and stores, and the expanded load/store instructions
+      // should have a valid discriminator.
+      if (!shouldHaveDiscriminator(&I))
         continue;
       const DILocation *DIL = I.getDebugLoc();
       if (!DIL)
@@ -207,6 +217,10 @@ static bool addDiscriminators(Function &F) {
     LocationSet CallLocations;
     for (auto &I : B.getInstList()) {
       CallInst *Current = dyn_cast<CallInst>(&I);
+      // We bypass intrinsic calls for the following two reasons:
+      //  1) We want to avoid a non-deterministic assigment of
+      //     discriminators.
+      //  2) We want to minimize the number of base discriminators used.
       if (!Current || isa<IntrinsicInst>(&I))
         continue;