JIT: fix profile propagation in LowerSwitch

src/coreclr/jit/compiler.h

@@ -6947,7 +6947,7 @@ class Compiler
     void fgDebugCheckFlagsHelper(GenTree* tree, GenTreeFlags actualFlags, GenTreeFlags expectedFlags);
     void fgDebugCheckTryFinallyExits();
     void fgDebugCheckProfile(PhaseChecks checks = PhaseChecks::CHECK_NONE);
-    bool fgDebugCheckProfileWeights(ProfileChecks checks);
+    bool fgDebugCheckProfileWeights(ProfileChecks checks, bool dump = false);
     bool fgDebugCheckIncomingProfileData(BasicBlock* block, ProfileChecks checks);
     bool fgDebugCheckOutgoingProfileData(BasicBlock* block, ProfileChecks checks);
 

src/coreclr/jit/fgprofile.cpp

@@ -4595,6 +4595,8 @@ void Compiler::fgDebugCheckProfile(PhaseChecks checks)
 //
 // Arguments:
 //   checks - checker options
+//   dump   - if true, report inconsistencies via JITDUMP without asserting (used by the
+//            re-run below to log details before the initial pass asserts)
 //
 // Returns:
 //   True if all enabled checks pass
@@ -4610,7 +4612,7 @@ void Compiler::fgDebugCheckProfile(PhaseChecks checks)
 //   There's no point checking until we've built pred lists, as
 //   we can't easily reason about consistency without them.
 //
-bool Compiler::fgDebugCheckProfileWeights(ProfileChecks checks)
+bool Compiler::fgDebugCheckProfileWeights(ProfileChecks checks, bool dump)
 {
     // We can check classic (min/max, late computed) weights
     //   and/or
@@ -4845,13 +4847,20 @@ bool Compiler::fgDebugCheckProfileWeights(ProfileChecks checks)
 
         // Note we only assert when we think the profile data should be consistent.
         //
-        if (assertOnFailure)
+        if (assertOnFailure && !dump)
         {
+            // Re-run with dumping forced on so the offending blocks are logged before we assert.
+            //
+            const bool wasVerbose = verbose;
+            verbose               = true;
+            fgDebugCheckProfileWeights(checks, /* dump */ true);
+            verbose = wasVerbose;
+
             assert(!"Inconsistent profile data");
         }
     }
 
-    if (unflaggedBlocks > 0)
+    if ((unflaggedBlocks > 0) && !dump)
     {
         JITDUMP("%d blocks are missing BBF_PROF_WEIGHT flag.\n", unflaggedBlocks);
         assert(!"Missing BBF_PROF_WEIGHT flag");

src/coreclr/jit/lower.cpp

@@ -1306,15 +1306,17 @@ GenTree* Lowering::LowerSwitch(GenTree* node)
                 bool           profileInconsistent = false;
                 for (unsigned i = 0; i < targetCnt; i++)
                 {
-                    FlowEdge* const edge          = uniqueSuccs[i];
-                    weight_t const  oldEdgeWeight = edge->getLikelyWeight();
+                    FlowEdge* const edge = uniqueSuccs[i];
                     edge->setLikelihood(newLikelihood * edge->getDupCount());
-                    weight_t const newEdgeWeight = edge->getLikelyWeight();
 
                     if (afterDefaultCondBlock->hasProfileWeight())
                     {
+                        // Recompute the target's weight from its incoming edges rather than adjusting
+                        // it incrementally: the earlier default-peel scaled afterDefaultCondBlock's
+                        // weight but left the switch targets' weights stale, so an incremental update
+                        // would accumulate on top of a stale value (see #130785).
                         BasicBlock* const targetBlock = edge->getDestinationBlock();
-                        targetBlock->increaseBBProfileWeight(newEdgeWeight - oldEdgeWeight);
+                        targetBlock->setBBProfileWeight(targetBlock->computeIncomingWeight());
                         profileInconsistent |= (targetBlock->NumSucc() > 0);
                     }
                 }