[ValueTracking] peek through min/max to find isKnownToBeAPowerOfTwo

This is similar to the select logic just ahead of the new code.
Min/max choose exactly one value from the inputs, so if both of
those are a power-of-2, then the result must be a power-of-2.

This might help with D98152, but we likely still need other
pieces of the puzzle to avoid regressions.

The change in PatternMatch.h is needed to build with clang.
It's possible there is a better way to deal with the 'const'
incompatibities.

Differential Revision: https://reviews.llvm.org/D99276

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 7984500..cd08c4e 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1977,6 +1977,12 @@ bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,
     return isKnownToBeAPowerOfTwo(SI->getTrueValue(), OrZero, Depth, Q) &&
            isKnownToBeAPowerOfTwo(SI->getFalseValue(), OrZero, Depth, Q);
 
+  // Peek through min/max.
+  if (match(V, m_MaxOrMin(m_Value(X), m_Value(Y)))) {
+    return isKnownToBeAPowerOfTwo(X, OrZero, Depth, Q) &&
+           isKnownToBeAPowerOfTwo(Y, OrZero, Depth, Q);
+  }
+
   if (OrZero && match(V, m_And(m_Value(X), m_Value(Y)))) {
     // A power of two and'd with anything is a power of two or zero.
     if (isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q) ||