Work around MemorySanitizer movmsk false positives
MemorySanitizer does not recognize the x86 movmskps and pmovmskb
instructions. In such cases it falls back to checking all input operands
for uninitialized bits. This causes false positives specifically with
Reactor's Byte8 type which is often loaded from memory, leaving the
upper 64-bit of an SSE register undefined.
This change masks out the unused parts of the input vector, leaving just
the sign bits.
Bug: b/172238865
Change-Id: I50c921a7ff8a4ebdba89136bb82c9f46ccdc3769
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/54268
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index dea359f..d36c2e8 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -3960,12 +3960,32 @@
RValue<Int> movmskps(RValue<Float4> x)
{
- return RValue<Int>(createInstruction(llvm::Intrinsic::x86_sse_movmsk_ps, x.value()));
+ Value *v = x.value();
+
+ // TODO(b/172238865): MemorySanitizer does not support movmsk instructions,
+ // which makes it look at the entire 128-bit input for undefined bits. Mask off
+ // just the sign bits to avoid false positives.
+ if(__has_feature(memory_sanitizer))
+ {
+ v = As<Float4>(As<Int4>(v) & Int4(0x80000000u)).value();
+ }
+
+ return RValue<Int>(createInstruction(llvm::Intrinsic::x86_sse_movmsk_ps, v));
}
RValue<Int> pmovmskb(RValue<Byte8> x)
{
- return RValue<Int>(createInstruction(llvm::Intrinsic::x86_sse2_pmovmskb_128, x.value())) & 0xFF;
+ Value *v = x.value();
+
+ // TODO(b/172238865): MemorySanitizer does not support movmsk instructions,
+ // which makes it look at the entire 128-bit input for undefined bits. Mask off
+ // just the sign bits in the lower 64-bit vector to avoid false positives.
+ if(__has_feature(memory_sanitizer))
+ {
+ v = As<Byte16>(As<Int4>(v) & Int4(0x80808080u, 0x80808080u, 0, 0)).value();
+ }
+
+ return RValue<Int>(createInstruction(llvm::Intrinsic::x86_sse2_pmovmskb_128, v)) & 0xFF;
}
RValue<Int4> pmovzxbd(RValue<Byte16> x)
