[llvm] 2d7f34f - [ValueTracking] Don't special case depth for phi of select (#114996)

[via llvm-commits]

Author: Nikita Popov
Date: 2024-11-07T10:14:28+01:00
New Revision: 2d7f34f2a5df9396a33a0ea044cfe3ddf33e1f5c

URL: https://github.com/llvm/llvm-project/commit/2d7f34f2a5df9396a33a0ea044cfe3ddf33e1f5c
DIFF: https://github.com/llvm/llvm-project/commit/2d7f34f2a5df9396a33a0ea044cfe3ddf33e1f5c.diff

LOG: [ValueTracking] Don't special case depth for phi of select (#114996)

As discussed on
https://github.com/llvm/llvm-project/pull/114689#pullrequestreview-2411822612
and following, there is no principled reason why the phi of select case
should have a different recursion limit than the general case. There may
still be fan-out, and there may still be indirect recursion. Revert that
part of #113707.

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 37cd4caaca71df..ed3fa35c5b8610 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1565,20 +1565,12 @@ static void computeKnownBitsFromOperator(const Operator *I,
         // Skip direct self references.
         if (IncValue == P) continue;
 
-        // Recurse, but cap the recursion to one level, because we don't
-        // want to waste time spinning around in loops.
-        // TODO: See if we can base recursion limiter on number of incoming phi
-        // edges so we don't overly clamp analysis.
-        unsigned IncDepth = MaxAnalysisRecursionDepth - 1;
-
         // If the Use is a select of this phi, use the knownbit of the other
         // operand to break the recursion.
         if (auto *SI = dyn_cast<SelectInst>(IncValue)) {
-          if (SI->getTrueValue() == P || SI->getFalseValue() == P) {
+          if (SI->getTrueValue() == P || SI->getFalseValue() == P)
             IncValue = SI->getTrueValue() == P ? SI->getFalseValue()
                                                : SI->getTrueValue();
-            IncDepth = Depth + 1;
-          }
         }
 
         // Change the context instruction to the "edge" that flows into the
@@ -1589,7 +1581,13 @@ static void computeKnownBitsFromOperator(const Operator *I,
         RecQ.CxtI = P->getIncomingBlock(u)->getTerminator();
 
         Known2 = KnownBits(BitWidth);
-        computeKnownBits(IncValue, DemandedElts, Known2, IncDepth, RecQ);
+
+        // Recurse, but cap the recursion to one level, because we don't
+        // want to waste time spinning around in loops.
+        // TODO: See if we can base recursion limiter on number of incoming phi
+        // edges so we don't overly clamp analysis.
+        computeKnownBits(IncValue, DemandedElts, Known2,
+                         MaxAnalysisRecursionDepth - 1, RecQ);
 
         // See if we can further use a conditional branch into the phi
         // to help us determine the range of the value.