[msan] Mostly disable msan-handle-icmp-exact.

It is way too slow. Change the default option value to 0.
Always do exact shadow propagation for unsigned ICmp with constants, it is
cheap (under 1% cpu time) and required for correctness.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173682 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 24 insertions, 6 deletions

diff --git a/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index a329dcc..714972e 100644
--- a/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -129,7 +129,7 @@ static cl::opt<bool> ClHandleICmp("msan-handle-icmp",
 
 static cl::opt<bool> ClHandleICmpExact("msan-handle-icmp-exact",
        cl::desc("exact handling of relational integer ICmp"),
-       cl::Hidden, cl::init(true));
+       cl::Hidden, cl::init(false));
 
 static cl::opt<bool> ClStoreCleanOrigin("msan-store-clean-origin",
        cl::desc("store origin for clean (fully initialized) values"),
@@ -1255,14 +1255,32 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   }
 
   void visitICmpInst(ICmpInst &I) {
-    if (ClHandleICmp && I.isEquality())
+    if (!ClHandleICmp) {
+      handleShadowOr(I);
+      return;
+    }
+    if (I.isEquality()) {
       handleEqualityComparison(I);
-    else if (ClHandleICmp && ClHandleICmpExact && I.isRelational())
+      return;
+    }
+
+    assert(I.isRelational());
+    if (ClHandleICmpExact) {
       handleRelationalComparisonExact(I);
-    else if (ClHandleICmp && I.isSigned() && I.isRelational())
+      return;
+    }
+    if (I.isSigned()) {
       handleSignedRelationalComparison(I);
-    else
-      handleShadowOr(I);
+      return;
+    }
+
+    assert(I.isUnsigned());
+    if ((isa<Constant>(I.getOperand(0)) || isa<Constant>(I.getOperand(1)))) {
+      handleRelationalComparisonExact(I);
+      return;
+    }
+
+    handleShadowOr(I);
   }
 
   void visitFCmpInst(FCmpInst &I) {