From d948b8fcb9d120afbbad5f26a74aa477caad99b0 Mon Sep 17 00:00:00 2001
From: Rick Lavoie <rlavoie@fb.com>
Date: Wed, 15 Sep 2021 21:38:16 -0700
Subject: [PATCH] Mandatorily remove non-DefConst constants in HHIR

Summary:
In HHIR, a SSATmp can be a constant (hasConstVal() true), but it's
source is not a DefConst. An example would be a function call which is
known to return a constant.

We try to const-prop all of these non-DefConst constants. That is, any
instruction which takes one of these constants is changed instead to
take the DefConst equivalent. This is important, as a SSATmp constant
might not have any Vrefs defined (in the function call example, we
don't write to %rax if the return value is known). This can lead to
assertions being triggered.

The simplifier can perform this const-prop. However, it was failing to
retype dst SSATmp types, meaning it would miss some cases. Add a call
to retypeDests to fix this.

Also, in some situations we may not call the simplifier. In this case,
we still need to do this "mandatory propagation", so do so.

Reviewed By: oulgen

Differential Revision: D30905689

fbshipit-source-id: c1f35639950fb0bb926ad9b3b5d49e2ac3df177f
---
 hphp/runtime/vm/jit/opt.cpp      | 18 ++++++++++++++++++
 hphp/runtime/vm/jit/simplify.cpp |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/hphp/runtime/vm/jit/opt.cpp b/hphp/runtime/vm/jit/opt.cpp
index 2e0b5faaf2b..53952956aea 100644
--- a/hphp/runtime/vm/jit/opt.cpp
+++ b/hphp/runtime/vm/jit/opt.cpp
@@ -23,6 +23,7 @@
 #include "hphp/runtime/vm/jit/ir-unit.h"
 #include "hphp/runtime/vm/jit/mutation.h"
 #include "hphp/runtime/vm/jit/print.h"
+#include "hphp/runtime/vm/jit/simple-propagation.h"
 #include "hphp/runtime/vm/jit/simplify.h"
 #include "hphp/runtime/vm/jit/timer.h"
 #include "hphp/runtime/vm/jit/dce.h"
@@ -161,6 +162,17 @@ uint64_t count_inline_returns(const IRUnit& unit) {
   return ret;
 }
 
+void mandatoryPropagation(IRUnit& unit) {
+  forEachInst(
+    rpoSortCfg(unit),
+    [&] (IRInstruction* inst) {
+      copyProp(inst);
+      constProp(unit, inst);
+      retypeDests(inst, &unit);
+     }
+  );
+}
+
 //////////////////////////////////////////////////////////////////////
 
 }
@@ -248,7 +260,13 @@ void optimize(IRUnit& unit, TransKind kind) {
   if (kind != TransKind::Profile && RuntimeOption::EvalHHIRSimplification) {
     rqtrace::EventGuard trace{"OPT_SIMPLIFY"};
     doPass(unit, simplifyPass, DCE::Full);
+  } else {
+    // If we don't run the simplifier, we still need to run mandatory
+    // propagation at least to remove the use of non-DefConst
+    // constants.
+    mandatoryPropagation(unit);
   }
+
   doPass(unit, fixBlockHints, DCE::None);
 
   if (kind == TransKind::Optimize) {
diff --git a/hphp/runtime/vm/jit/simplify.cpp b/hphp/runtime/vm/jit/simplify.cpp
index 60492d9f788..e4cf171dc53 100644
--- a/hphp/runtime/vm/jit/simplify.cpp
+++ b/hphp/runtime/vm/jit/simplify.cpp
@@ -40,6 +40,7 @@
 #include "hphp/runtime/vm/jit/ir-builder.h"
 #include "hphp/runtime/vm/jit/irgen-internal.h"
 #include "hphp/runtime/vm/jit/minstr-effects.h"
+#include "hphp/runtime/vm/jit/mutation.h"
 #include "hphp/runtime/vm/jit/simple-propagation.h"
 #include "hphp/runtime/vm/jit/translator-runtime.h"
 #include "hphp/runtime/vm/jit/type-array-elem.h"
@@ -4010,6 +4011,7 @@ void simplifyInPlace(IRUnit& unit, IRInstruction* origInst) {
 
   copyProp(origInst);
   constProp(unit, origInst);
+  retypeDests(origInst, &unit);
   auto res = simplify(unit, origInst);
 
   // No simplification occurred; nothing to do.
-- 
2.11.4.GIT