[InstCombine][asan] Don't speculate loads before `select ptr` (#100773)

Even if memory is valid from `llvm` point of view,
e.g. local alloca, sanitizers have API for user
specific memory annotations.

These annotations can be used to track size of the
local object, e.g. inline vectors may prevent
accesses beyond the current vector size.

So valid programs should not access those parts of
alloca before checking preconditions.

Fixes #100639.

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp
index 1704f0d..a88469a 100644
--- a/llvm/lib/Analysis/Loads.cpp
+++ b/llvm/lib/Analysis/Loads.cpp
@@ -378,8 +378,12 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Align Alignment, const APInt &S
   // If DT is not specified we can't make context-sensitive query
   const Instruction* CtxI = DT ? ScanFrom : nullptr;
   if (isDereferenceableAndAlignedPointer(V, Alignment, Size, DL, CtxI, AC, DT,
-                                         TLI))
-    return true;
+                                         TLI)) {
+    // With sanitizers `Dereferenceable` is not always enough for unconditional
+    // load.
+    if (!ScanFrom || !suppressSpeculativeLoadForSanitizers(*ScanFrom))
+      return true;
+  }
 
   if (!ScanFrom)
     return false;