[Debug] Retain both copies of debug intrinsics in HoistThenElseCodeToIf

When hoisting common code from the "then" and "else" branches of a condition
to before the "if", the HoistThenElseCodeToIf routine will attempt to merge
the debug location associated with the two original copies of the hoisted
instruction.

This is a problem in the special case where the hoisted instruction is a
debug info intrinsic, since for those the debug location is considered
part of the intrinsic and attempting to modify it may resut in invalid
IR.  This is the underlying cause of PR36410.

This patch fixes the problem by handling debug info intrinsics specially:
instead of hoisting one copy and merging the two locations, the code now
simply hoists both copies, each with its original location intact.  Note
that this is still only done in the case where both original copies are
otherwise (i.e. apart from location metadata) identical.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D44312

llvm-svn: 327622

1 files changed, 38 insertions, 25 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 82ef1b91e74..f1cd4cfdf3f 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1290,31 +1290,44 @@ static bool HoistThenElseCodeToIf(BranchInst *BI,
     if (!TTI.isProfitableToHoist(I1) || !TTI.isProfitableToHoist(I2))
       return Changed;
 
-    // For a normal instruction, we just move one to right before the branch,
-    // then replace all uses of the other with the first.  Finally, we remove
-    // the now redundant second instruction.
-    BIParent->getInstList().splice(BI->getIterator(), BB1->getInstList(), I1);
-    if (!I2->use_empty())
-      I2->replaceAllUsesWith(I1);
-    I1->andIRFlags(I2);
-    unsigned KnownIDs[] = {LLVMContext::MD_tbaa,
-                           LLVMContext::MD_range,
-                           LLVMContext::MD_fpmath,
-                           LLVMContext::MD_invariant_load,
-                           LLVMContext::MD_nonnull,
-                           LLVMContext::MD_invariant_group,
-                           LLVMContext::MD_align,
-                           LLVMContext::MD_dereferenceable,
-                           LLVMContext::MD_dereferenceable_or_null,
-                           LLVMContext::MD_mem_parallel_loop_access};
-    combineMetadata(I1, I2, KnownIDs);
-
-    // I1 and I2 are being combined into a single instruction.  Its debug
-    // location is the merged locations of the original instructions.
-    I1->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc());
-
-    I2->eraseFromParent();
-    Changed = true;
+    if (isa<DbgInfoIntrinsic>(I1) || isa<DbgInfoIntrinsic>(I2)) {
+      assert (isa<DbgInfoIntrinsic>(I1) && isa<DbgInfoIntrinsic>(I2));
+      // The debug location is an integral part of a debug info intrinsic
+      // and can't be separated from it or replaced.  Instead of attempting
+      // to merge locations, simply hoist both copies of the intrinsic.
+      BIParent->getInstList().splice(BI->getIterator(),
+                                     BB1->getInstList(), I1);
+      BIParent->getInstList().splice(BI->getIterator(),
+                                     BB2->getInstList(), I2);
+      Changed = true;
+    } else {
+      // For a normal instruction, we just move one to right before the branch,
+      // then replace all uses of the other with the first.  Finally, we remove
+      // the now redundant second instruction.
+      BIParent->getInstList().splice(BI->getIterator(),
+                                     BB1->getInstList(), I1);
+      if (!I2->use_empty())
+        I2->replaceAllUsesWith(I1);
+      I1->andIRFlags(I2);
+      unsigned KnownIDs[] = {LLVMContext::MD_tbaa,
+                             LLVMContext::MD_range,
+                             LLVMContext::MD_fpmath,
+                             LLVMContext::MD_invariant_load,
+                             LLVMContext::MD_nonnull,
+                             LLVMContext::MD_invariant_group,
+                             LLVMContext::MD_align,
+                             LLVMContext::MD_dereferenceable,
+                             LLVMContext::MD_dereferenceable_or_null,
+                             LLVMContext::MD_mem_parallel_loop_access};
+      combineMetadata(I1, I2, KnownIDs);
+
+      // I1 and I2 are being combined into a single instruction.  Its debug
+      // location is the merged locations of the original instructions.
+      I1->applyMergedLocation(I1->getDebugLoc(), I2->getDebugLoc());
+
+      I2->eraseFromParent();
+      Changed = true;
+    }
 
     I1 = &*BB1_Itr++;
     I2 = &*BB2_Itr++;