From e1287f556f4f9befaa55c205e3b5a9429d897083 Mon Sep 17 00:00:00 2001
From: Evgeniy Stepanov <eugeni.stepanov@gmail.com>
Date: Thu, 17 Jul 2014 09:10:37 +0000
Subject: [PATCH] [msan] Avoid redundant origin stores.

Origin is meaningless for fully initialized values. Avoid
storing origin for function arguments that are known to
be always initialized (i.e. shadow is a compile-time null
constant).

This is not about correctness, but purely an optimization.
Seems to affect compilation time of blacklisted functions
significantly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213239 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../Instrumentation/MemorySanitizer.cpp        |  5 ++++-
 .../MemorySanitizer/msan_basic.ll              | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 496ab4877e0..57e308c20db 100644
--- a/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -2313,6 +2313,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
       Value *ArgShadowBase = getShadowPtrForArgument(A, IRB, ArgOffset);
       DEBUG(dbgs() << "  Arg#" << i << ": " << *A <<
             " Shadow: " << *ArgShadow << "\n");
+      bool ArgIsInitialized = false;
       if (CS.paramHasAttr(i + 1, Attribute::ByVal)) {
         assert(A->getType()->isPointerTy() &&
                "ByVal argument is not a pointer!");
@@ -2325,8 +2326,10 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
         Size = MS.DL->getTypeAllocSize(A->getType());
         Store = IRB.CreateAlignedStore(ArgShadow, ArgShadowBase,
                                        kShadowTLSAlignment);
+        Constant *Cst = dyn_cast<Constant>(ArgShadow);
+        if (Cst && Cst->isNullValue()) ArgIsInitialized = true;
       }
-      if (MS.TrackOrigins)
+      if (MS.TrackOrigins && !ArgIsInitialized)
         IRB.CreateStore(getOrigin(A),
                         getOriginPtrForArgument(A, IRB, ArgOffset));
       (void)Store;
diff --git a/test/Instrumentation/MemorySanitizer/msan_basic.ll b/test/Instrumentation/MemorySanitizer/msan_basic.ll
index 51693cdd567..0faf45d70c5 100644
--- a/test/Instrumentation/MemorySanitizer/msan_basic.ll
+++ b/test/Instrumentation/MemorySanitizer/msan_basic.ll
@@ -766,6 +766,24 @@ cond.end:                                         ; preds = %cond.false, %cond.t
 ; CHECK: ret i32 [[A]]
 
 
+; Test that there are no __msan_param_origin_tls stores when
+; argument shadow is a compile-time zero constant (which is always the case
+; in functions missing sanitize_memory attribute).
+
+define i32 @NoSanitizeMemoryParamTLS(i32* nocapture readonly %x) {
+entry:
+  %0 = load i32* %x, align 4
+  %call = tail call i32 @NoSanitizeMemoryParamTLSHelper(i32 %0)
+  ret i32 %call
+}
+
+declare i32 @NoSanitizeMemoryParamTLSHelper(i32 %x)
+
+; CHECK-LABEL: define i32 @NoSanitizeMemoryParamTLS(
+; CHECK-NOT: __msan_param_origin_tls
+; CHECK: ret i32
+
+
 ; Test argument shadow alignment
 
 define <2 x i64> @ArgumentShadowAlignment(i64 %a, <2 x i64> %b) sanitize_memory {