[llvm] 9106960 - [Assignment Tracking][SROA] Don't un-poison dbg.assigns using multiple loc ops

[via llvm-commits]

Author: OCHyams
Date: 2023-04-11T18:18:11+01:00
New Revision: 9106960724b5c8b0e3ba333238571cbbd3c10130

URL: https://github.com/llvm/llvm-project/commit/9106960724b5c8b0e3ba333238571cbbd3c10130
DIFF: https://github.com/llvm/llvm-project/commit/9106960724b5c8b0e3ba333238571cbbd3c10130.diff

LOG: [Assignment Tracking][SROA] Don't un-poison dbg.assigns using multiple loc ops

Some dbg.assigns using poison become un-poisoned in SROA. The reason this
happens at all is because dbg.assigns linked to memory intrinsics use poison to
indicate they can't describe the stored value, but the value becomes available
after some optimisations. This needs reworking eventually, but for now we need
to ensure that when it does occur we don't create invalid expressions.

D147312 prevented this occuring when the dbg.assign uses DIArgLists, but that
wasn't a complete fix. We also need to ensure we avoid un-poisoning when the
existing expression uses more than one location operand (DW_OP_arg, n).

Reviewed By: jmorse

Differential Revision: https://reviews.llvm.org/D148020

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/SROA.cpp
    llvm/test/DebugInfo/Generic/assignment-tracking/sroa/fail-fragment.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index f7011672c8b5f..a58dcff466e3b 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -302,7 +302,9 @@ static void migrateDebugInfo(AllocaInst *OldAlloca, bool IsSplit,
     // This should be a very rare situation as it requires the value being
     // stored to 
diff er from the dbg.assign (i.e., the value has been
     // represented 
diff erently in the debug intrinsic for some reason).
-    SetKillLocation |= DbgAssign->hasArgList() && Value;
+    SetKillLocation |=
+        Value && (DbgAssign->hasArgList() ||
+                  !DbgAssign->getExpression()->isSingleLocationExpression());
     if (SetKillLocation)
       NewAssign->setKillLocation();
 

diff  --git a/llvm/test/DebugInfo/Generic/assignment-tracking/sroa/fail-fragment.ll b/llvm/test/DebugInfo/Generic/assignment-tracking/sroa/fail-fragment.ll
index 5aa9ce3a32ff9..d9ded4839a982 100644
--- a/llvm/test/DebugInfo/Generic/assignment-tracking/sroa/fail-fragment.ll
+++ b/llvm/test/DebugInfo/Generic/assignment-tracking/sroa/fail-fragment.ll
@@ -5,6 +5,10 @@
 ;; it used a fragment that can't be split (the first check directive below).
 ;; NOTE: If createFragmentExpression gets smarter it may be necessary to create
 ;; a new test case.
+;; In some cases a dbg.assign with a poison value is replaced with a non-poison
+;; value. This needs reworking, but as a stop-gap we need to ensure this
+;; doesn't cause invalid expressions to be created. Check we don't do it when
+;; the expression uses more than one location operand (DW_OP_arg n).
 
 ; CHECK: if.then:
 ; CHECK: dbg.value(metadata i32 poison, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32))
@@ -15,6 +19,9 @@
 ; CHECK: dbg.value(metadata i32 2, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32))
 ; CHECK: dbg.value(metadata i32 0, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 32, 32))
 
+; CHECK: if.inner:
+; CHECK: call void @llvm.dbg.value(metadata i32 poison, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value))
+
 ; CHECK: end:
 ; CHECK: dbg.value(metadata i32 %{{.*}}, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32))
 
@@ -37,6 +44,11 @@ if.then:
 if.else:
   store i64 2, ptr %codepoint, align 4, !DIAssignID !28
   call void @llvm.dbg.assign(metadata i32 2, metadata !15, metadata !DIExpression(), metadata !28, metadata ptr %codepoint, metadata !DIExpression()), !dbg !26
+  br i1 %cmp, label %end, label %if.inner
+
+if.inner:
+  store i32 3, ptr %codepoint, align 4, !DIAssignID !29
+  call void @llvm.dbg.assign(metadata i32 poison, metadata !15, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value), metadata !29, metadata ptr %codepoint, metadata !DIExpression()), !dbg !26
   br label %end
 
 end:
@@ -63,3 +75,4 @@ declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata,
 !26 = !DILocation(line: 0, scope: !18)
 !27 = distinct !DIAssignID()
 !28 = distinct !DIAssignID()
+!29 = distinct !DIAssignID()