[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

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/test/Instrumentation/MemorySanitizer/msan_basic.ll b/llvm/test/Instrumentation/MemorySanitizer/msan_basic.ll
index 51693cdd567..0faf45d70c5 100644
--- 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 {