[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.

llvm-svn: 213239

diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 496ab4877e0304a42aad3b1c591b44a7cddf8fd0..57e308c20dba42b594ac28c21fcef28a5f66de97 100644 (file)
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/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/llvm/test/Instrumentation/MemorySanitizer/msan_basic.ll b/llvm/test/Instrumentation/MemorySanitizer/msan_basic.ll
index 51693cdd567b5275427c37693980e949db27c6a3..0faf45d70c5930e8a26a73e18a8d5bbff844c288 100644 (file)
--- a/llvm/test/Instrumentation/MemorySanitizer/msan_basic.ll
+++ b/llvm/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 {