[Analysis] isDereferenceableAndAlignedPointer(): recurse into select's hands

By doing this within the method itself,
we support traversing multiple levels of selects (TODO: PHI's),
fixing the SROA `std::clamp()` testcase.

Fixes https://bugs.llvm.org/show_bug.cgi?id=47271
Mostly fixes https://bugs.llvm.org/show_bug.cgi?id=49909

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp
index 8d01ea0..2ae1fd5 100644
--- a/llvm/lib/Analysis/Loads.cpp
+++ b/llvm/lib/Analysis/Loads.cpp
@@ -59,6 +59,16 @@ static bool isDereferenceableAndAlignedPointer(
   // Note that it is not safe to speculate into a malloc'd region because
   // malloc may return null.
 
+  // Recurse into both hands of select.
+  if (const SelectInst *Sel = dyn_cast<SelectInst>(V)) {
+    return isDereferenceableAndAlignedPointer(Sel->getTrueValue(), Alignment,
+                                              Size, DL, CtxI, DT, TLI, Visited,
+                                              MaxDepth) &&
+           isDereferenceableAndAlignedPointer(Sel->getFalseValue(), Alignment,
+                                              Size, DL, CtxI, DT, TLI, Visited,
+                                              MaxDepth);
+  }
+
   // bitcast instructions are no-ops as far as dereferenceability is concerned.
   if (const BitCastOperator *BC = dyn_cast<BitCastOperator>(V)) {
     if (BC->getSrcTy()->isPointerTy())