[msan] Enable msan-check-constant-shadow by default

[vitalybuka]

Summary

Depends on D132761.

[vitalybuka]

rebase

[eugenis]

LGTM

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

ClEnableKmsan("msan-kernel",
                   cl::desc("Enable KernelMemorySanitizer instrumentation"),
                   cl::Hidden, cl::init(false));
 
 static cl::opt<bool>
     ClDisableChecks("msan-disable-checks",
                     cl::desc("Apply no_sanitize to the whole file"), cl::Hidden,
                     cl::init(false));
 
-// This is an experiment to enable handling of cases where shadow is a non-zero
-// compile-time constant. For some unexplainable reason they were silently
-// ignored in the instrumentation.
 static cl::opt<bool>
     ClCheckConstantShadow("msan-check-constant-shadow",
                           cl::desc("Insert checks for constant shadow values"),
-                          cl::Hidden, cl::init(false));
+                          cl::Hidden, cl::init(true));
 
 // This is off by default because of a bug in gold:
 // https://sourceware.org/bugzilla/show_bug.cgi?id=19002
 static cl::opt<bool>
     ClWithComdat("msan-with-comdat",
                  cl::desc("Place MSan constructors in comdat sections"),
                  cl::Hidden, cl::init(false));
 
struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   Value *getShadow(Instruction *I, int i) {
     return getShadow(I->getOperand(i));
   }
 
   /// Get the origin for a value.
   Value *getOrigin(Value *V) {
     if (!MS.TrackOrigins)
       return nullptr;
-    if (!PropagateShadow)
-      return getCleanOrigin();
-    if (isa<Constant>(V))
+    if (!PropagateShadow || isa<Constant>(V) || isa<InlineAsm>(V))
       return getCleanOrigin();
     assert((isa<Instruction>(V) || isa<Argument>(V)) &&
            "Unexpected value type in getOrigin()");
     if (Instruction *I = dyn_cast<Instruction>(V)) {
       if (I->getMetadata(LLVMContext::MD_nosanitize))
         return getCleanOrigin();
     }
     Value *Origin = OriginMap[V];

llvm/test/Instrumentation/MemorySanitizer/check-constant-shadow.ll

-; RUN: opt < %s -msan-check-access-address=0 -msan-check-constant-shadow=1 -msan-eager-checks=1 -msan-track-origins=1 -S -passes=msan 2>&1 | FileCheck --check-prefixes=CHECK,CONST %s --implicit-check-not=icmp --implicit-check-not="store i" --implicit-check-not="call void @__msan"
-; RUN: opt < %s -msan-check-access-address=0                               -msan-eager-checks=1 -msan-track-origins=1 -S -passes=msan 2>&1 | FileCheck --check-prefixes=CHECK       %s --implicit-check-not=icmp --implicit-check-not="store i" --implicit-check-not="call void @__msan"
+; RUN: opt < %s -msan-check-access-address=0                               -msan-eager-checks=1 -msan-track-origins=1 -S -passes=msan 2>&1 | FileCheck --check-prefixes=CHECK,CONST %s --implicit-check-not=icmp --implicit-check-not="store i" --implicit-check-not="call void @__msan"
+; RUN: opt < %s -msan-check-access-address=0 -msan-check-constant-shadow=0 -msan-eager-checks=1 -msan-track-origins=1 -S -passes=msan 2>&1 | FileCheck --check-prefixes=CHECK       %s --implicit-check-not=icmp --implicit-check-not="store i" --implicit-check-not="call void @__msan"
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 ; Test that returning a literal undef from main() triggers an MSan warning.
 
 ; main() is special: it inserts check for the return value
 define i32 @main() nounwind uwtable sanitize_memory {