From aa38055cca67d9ece504cef2adc8a19f0cb2ec8e Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Sat, 13 May 2023 07:42:33 -0700
Subject: [PATCH] JIT: do early block merging in more cases (#86157)

OSR and PGO both rely on the fact that the early flowgraph the JIT builds is
the same flowgraph as the one seen in a previous JIT complation of that method,
since there is metadata (patchpoint offset, pgo schema) that refers to the
flowgraph. Previous work here (#85860) didn't ensure this for enough cases.

In particular if Tier0 does not do early block merging, but OSR does, it's possible
for the OSR entry point to fall within a merged block range, which the JIT is not
prepared to handle. This lead to the asserts seen in #86125.

The fix is to enable early block merging unless we're truly in a minopts or
debug codegen mode (previous to this Tier0 would not merge unless it also
was instrumenting; now it will always merge).

An alternative fix would be to find the block containing the OSR entry IL
offset, scan its statements, and split the block at the right spot, but that
seemed more involved.

Fixes #86125.
---
 src/coreclr/jit/compiler.h   | 16 ++++++++++++----
 src/coreclr/jit/fgbasic.cpp  |  4 ++--
 src/coreclr/jit/importer.cpp |  2 +-
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/coreclr/jit/compiler.h b/src/coreclr/jit/compiler.h
index 3b777c5..9dd385f 100644
--- a/src/coreclr/jit/compiler.h
+++ b/src/coreclr/jit/compiler.h
@@ -9393,11 +9393,19 @@ public:
             return IsInstrumented() && jitFlags->IsSet(JitFlags::JIT_FLAG_BBOPT);
         }
 
-        bool CanBeInstrumentedOrIsOptimized() const
+        bool DoEarlyBlockMerging() const
         {
-            return IsInstrumented() || (jitFlags->IsSet(JitFlags::JIT_FLAG_TIER0) &&
-                                        jitFlags->IsSet(JitFlags::JIT_FLAG_BBINSTR_IF_LOOPS)) ||
-                   jitFlags->IsSet(JitFlags::JIT_FLAG_BBOPT);
+            if (jitFlags->IsSet(JitFlags::JIT_FLAG_DEBUG_EnC) || jitFlags->IsSet(JitFlags::JIT_FLAG_DEBUG_CODE))
+            {
+                return false;
+            }
+
+            if (jitFlags->IsSet(JitFlags::JIT_FLAG_MIN_OPT) && !jitFlags->IsSet(JitFlags::JIT_FLAG_TIER0))
+            {
+                return false;
+            }
+
+            return true;
         }
 
         // true if we should use the PINVOKE_{BEGIN,END} helpers instead of generating
diff --git a/src/coreclr/jit/fgbasic.cpp b/src/coreclr/jit/fgbasic.cpp
index 0e00991..61f2c84 100644
--- a/src/coreclr/jit/fgbasic.cpp
+++ b/src/coreclr/jit/fgbasic.cpp
@@ -1840,7 +1840,7 @@ void Compiler::fgFindJumpTargets(const BYTE* codeAddr, IL_OFFSET codeSize, Fixed
 
                 if ((jmpDist == 0) &&
                     (opcode == CEE_LEAVE || opcode == CEE_LEAVE_S || opcode == CEE_BR || opcode == CEE_BR_S) &&
-                    opts.CanBeInstrumentedOrIsOptimized())
+                    opts.DoEarlyBlockMerging())
                 {
                     break; /* NOP */
                 }
@@ -2989,7 +2989,7 @@ unsigned Compiler::fgMakeBasicBlocks(const BYTE* codeAddr, IL_OFFSET codeSize, F
 
                 jmpDist = (sz == 1) ? getI1LittleEndian(codeAddr) : getI4LittleEndian(codeAddr);
 
-                if ((jmpDist == 0) && (opcode == CEE_BR || opcode == CEE_BR_S) && opts.CanBeInstrumentedOrIsOptimized())
+                if ((jmpDist == 0) && (opcode == CEE_BR || opcode == CEE_BR_S) && opts.DoEarlyBlockMerging())
                 {
                     continue; /* NOP */
                 }
diff --git a/src/coreclr/jit/importer.cpp b/src/coreclr/jit/importer.cpp
index 22c2552..14866e1 100644
--- a/src/coreclr/jit/importer.cpp
+++ b/src/coreclr/jit/importer.cpp
@@ -7420,7 +7420,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
             case CEE_BR_S:
                 jmpDist = (sz == 1) ? getI1LittleEndian(codeAddr) : getI4LittleEndian(codeAddr);
 
-                if ((jmpDist == 0) && opts.CanBeInstrumentedOrIsOptimized())
+                if ((jmpDist == 0) && opts.DoEarlyBlockMerging())
                 {
                     break; /* NOP */
                 }
-- 
2.7.4