[InstCombine] Support folding intrinsics into phis (#151115)

Call foldOpIntoPhi() for speculatable intrinsics. We already do this for
FoldOpIntoSelect().

Among other things, this partially subsumes
https://github.com/llvm/llvm-project/pull/149858.

2 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 1b78ace..47e017e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3891,16 +3891,20 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   }
   }
 
-  // Try to fold intrinsic into select operands. This is legal if:
+  // Try to fold intrinsic into select/phi operands. This is legal if:
   //  * The intrinsic is speculatable.
   //  * The select condition is not a vector, or the intrinsic does not
   //    perform cross-lane operations.
   if (isSafeToSpeculativelyExecuteWithVariableReplaced(&CI) &&
       isNotCrossLaneOperation(II))
-    for (Value *Op : II->args())
+    for (Value *Op : II->args()) {
       if (auto *Sel = dyn_cast<SelectInst>(Op))
         if (Instruction *R = FoldOpIntoSelect(*II, Sel))
           return R;
+      if (auto *Phi = dyn_cast<PHINode>(Op))
+        if (Instruction *R = foldOpIntoPhi(*II, Phi))
+          return R;
+    }
 
   if (Instruction *Shuf = foldShuffledIntrinsicOperands(II))
     return Shuf;
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 9e33320..b992597 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1994,6 +1994,8 @@ Instruction *InstCombinerImpl::foldOpIntoPhi(Instruction &I, PHINode *PN,
       }
       Clone = InsertNewInstBefore(Clone, OpBB->getTerminator()->getIterator());
       Clones.insert({OpBB, Clone});
+      // We may have speculated the instruction.
+      Clone->dropUBImplyingAttrsAndMetadata();
     }
 
     NewPhiValues[OpIndex] = Clone;